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Document and Entity Information - shares	6 Months Ended
Document and Entity Information - shares	Jun. 30, 2018	Jul. 31, 2018
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q2
Trading Symbol	STIM
Entity Registrant Name	NEURONETICS, INC.
Entity Central Index Key	0001227636
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding		17,577,047

Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 14,544	$ 29,147
Accounts receivable, net	4,724	4,267
Inventory	2,441	2,468
Prepaid expenses and other current assets	4,292	1,123
Total current assets	26,001	37,005
Property and equipment, net	1,493	1,359
Other assets	851	574
Total Assets	28,345	38,938
Current liabilities:
Accounts payable	2,928	2,513
Accrued expenses	7,731	7,511
Deferred revenue	1,686	1,970
Current portion of long-term debt	2,500
Total current liabilities	14,845	11,994
Long-term debt, net	27,497	29,556
Deferred revenue	2,124	2,275
Convertible preferred stock warrant liability	1,893	478
Deferred rent	121	151
Total Liabilities	46,480	44,454
Commitments and contingencies (Note 14)
Convertible preferred stock, $0.01 par value: 308,593 shares authorized, issuable in series; 304,958 shares issued and outstanding at June 30, 2018 and December 31, 2017; aggregate liquidation value of $108,324 at June 30, 2018	187,136	187,136
Stockholders’ deficit:
Preferred stock, $0.01 par value: no shares authorized, issued or outstanding at June 30, 2018 and December 31, 2017
Common stock, $0.01 par value: 413,918 shares authorized; 257 and 231 shares issued and outstanding at June 30, 2018 and December 31, 2017, respectively	3	2
Additional paid-in capital	4,665	4,292
Accumulated deficit	(209,939)	(196,946)
Total Stockholder’s Deficit	(205,271)	(192,652)
Total Liabilities, Convertible Preferred Stock and Stockholders’ Deficit	$ 28,345	$ 38,938

Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Statement Of Financial Position [Abstract]
Convertible preferred stock, par value	$ 0.01	$ 0.01
Convertible preferred stock, authorized	308,593,000	308,593,000
Convertible preferred stock, issued	304,958,000	304,958,000
Convertible preferred stock, outstanding	304,958,000	304,958,000
Liquidation preference	$ 108,324	$ 108,324
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	0	0
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	413,918,000	413,918,000
Common stock, shares issued	257,000	231,000
Common stock, shares outstanding	257,000	231,000

Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Income Statement [Abstract]
Revenues	$ 13,252	$ 10,308	$ 23,404	$ 17,834
Cost of revenues	3,245	2,501	5,702	4,039
Gross Profit	10,007	7,807	17,702	13,795
Operating expenses:
Sales and marketing	9,835	6,400	17,944	12,706
General and administrative	3,078	1,837	5,714	3,479
Research and development	2,330	2,147	3,885	4,175
Total operating expenses	15,243	10,384	27,543	20,360
Loss from Operations	(5,236)	(2,577)	(9,841)	(6,565)
Other (income) expense:
Interest expense	900	711	1,821	1,261
Other expense (income), net	1,360	(420)	1,331	(444)
Net Loss	$ (7,496)	$ (2,868)	$ (12,993)	$ (7,382)
Net loss per share of common stock outstanding, basic and diluted	$ (30.60)	$ (16.58)	$ (55.29)	$ (43.42)
Weighted-average common shares outstanding, basic and diluted	245	173	235	170

Statement of Changes in Convertible Preferred Stock and Stockholders' Deficit - 6 months ended Jun. 30, 2018 - USD ($) $ in Thousands	Total	Convertible Preferred Stock	Common Stock	Additional Paid-in Capital	Accumulated Deficit
Beginning balance at Dec. 31, 2017	$ (192,652)		$ 2	$ 4,292	$ (196,946)
Beginning balance, shares at Dec. 31, 2017			231,000
Beginning balance, shares at Dec. 31, 2017	304,958,000	304,958,000
Beginning balance at Dec. 31, 2017	$ 187,136	$ 187,136
Exercises of stock options	38		$ 1	37
Exercises of stock options, shares			26,000
Share-based compensation expense	336			336
Net loss	(12,993)				(12,993)
Ending balance at Jun. 30, 2018	$ (205,271)		$ 3	$ 4,665	$ (209,939)
Ending balance, shares at Jun. 30, 2018			257,000
Ending balance, shares at Jun. 30, 2018	304,958,000	304,958,000
Ending balance at Jun. 30, 2018	$ 187,136	$ 187,136

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References + Details

Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Cash Flows from Operating Activities:
Net loss	$ (12,993)	$ (7,382)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	463	307
Share-based compensation	336	198
Non-cash interest expense	441	285
Change in fair value of convertible preferred stock warrant liability	1,415	(411)
Cost of rental units purchased by customers	79	54
Changes in certain assets and liabilities:
Accounts receivable, net	(457)	37
Inventory	(378)	(569)
Prepaid expenses and other assets	380	152
Accounts payable	(89)	(1,270)
Accrued expenses	(2,130)	(763)
Deferred revenue	(435)	(101)
Deferred rent	(29)	(18)
Net Cash Used in Operating Activities	(13,397)	(9,481)
Cash Flows from Investing Activities:
Purchases of property and equipment and capitalized software	(513)	(152)
Net Cash Used in Investing Activities	(513)	(152)
Cash Flows from Financing Activities:
Payments of initial public offering costs	(731)
Proceeds from exercises of stock options	38	16
Proceeds from issuance of Series G convertible preferred stock, net		14,825
Borrowings under credit facilities		5,000
Payments of debt issuance costs		(1,015)
Net Cash (Used in) Provided by Financing Activities	(693)	18,826
Net (Decrease) Increase in Cash and Cash Equivalents	(14,603)	9,193
Cash and Cash Equivalents, Beginning of Period	29,147	17,040
Cash and Cash Equivalents, End of Period	14,544	26,233
Supplemental disclosure of cash flow information:
Cash paid for interest	1,334	992
Transfer of inventory to property and equipment	261	205
Supplemental disclosure of non-cash financing activities:
Allocation of proceeds from debt financing to convertible preferred stock warrant liability		$ 171
Deferred initial public offering costs included in accounts payable and accrued expenses	$ 2,542

Description of Business

6 Months Ended

Jun. 30, 2018

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Description of Business

1.	DESCRIPTION OF BUSINESS

Neuronetics, Inc., or the Company, is a commercial stage medical technology company focused on designing, developing and marketing products that improve the quality of life for patients who suffer from psychiatric disorders. The Company’s first commercial product, the NeuroStar Advanced Therapy System, is a non-invasive and non-systemic office-based treatment that uses transcranial magnetic stimulation, or TMS, to create a pulsed, MRI-strength magnetic field that induces electrical currents designed to stimulate specific areas of the brain associated with mood. The system was cleared in 2008 by the United States Food and Drug Administration, or the FDA, to treat adult patients with major depressive disorder, or MDD, who have failed to achieve satisfactory improvement from prior antidepressant medication in the current episode. The Company intends to continue to pursue development of its NeuroStar Advanced Therapy System for additional indications.

Initial Public Offering

On July 2, 2018, the Company closed its initial public offering, or IPO, in which the Company issued and sold 6.325 million shares of its common stock, which included the exercise of the underwriters’ option to purchase an additional 0.825 million shares of common stock, at a public offering price of $17.00 per share. The Company received net proceeds of $100.0 million after deducting underwriting discounts and commissions of $7.5 million but before deducting other offering expenses. The Company’s common stock is listed on the Nasdaq Global Market under the trading symbol “STIM.” In addition, upon the closing of the IPO on July 2, 2018, (i) all of the Company’s outstanding shares of convertible preferred stock converted into 11.0 million shares of common stock; (ii) all of the Company’s outstanding warrants to purchase convertible preferred stock converted into warrants to purchase common stock; and (iii) the Company filed an amended and restated certificate of incorporation to, among other things, decrease the number of shares of common stock, $0.01 par value per share, authorized for issuance to 200.0 million and to authorize the board of directors to issue up to 10.0 million shares of “blank check” preferred stock, $0.01 par value per share.

Liquidity

As of June 30, 2018, the Company had cash and cash equivalents of $14.5 million and an accumulated deficit of $209.9 million. The Company incurred negative cash flows from operating activities of $11.1 million for the year ended December 31, 2017 and $13.4 million for the six months ended June 30, 2018. The Company has incurred operating losses since its inception, and management anticipates that its operating losses will continue in the near term as the Company seeks to expand its sales and marketing initiatives to support its growth into existing and new markets and invest in additional research and development activities. The Company’s primary sources of capital to date have been from its IPO, private placements of its convertible preferred securities, borrowings under its credit facilities and revenues from sales of its products. As of June 30, 2018, the Company had $30.0 million of borrowings outstanding under its credit facility, which matures in March 2022. Management believes that the Company’s cash and cash equivalents as of June 30, 2018, proceeds from its IPO and revenues from sales of its products are sufficient to fund the Company’s operations for at least the next 24 months after June 30, 2018.

Basis of Presentation

6 Months Ended

Jun. 30, 2018

Accounting Policies [Abstract]

Basis of Presentation

2.	BASIS OF PRESENTATION

The accompanying financial statements have been prepared in accordance with accounting principles generally accepted in the United States, or GAAP. Any reference in these notes to applicable guidance is meant to refer to GAAP as found in the Accounting Standards Codification, or ASC, and Accounting Standards Updates, or ASU, promulgated by the Financial Accounting Standards Board, or FASB.

Interim Financial Statements

The accompanying unaudited interim financial statements have been prepared from the books and records of the Company in accordance with GAAP for interim financial information and Rule 10-01 of Regulation S-X promulgated by the United States Securities and Exchange Commission, or SEC, which permit reduced disclosures for interim periods. All adjustments, consisting only of normal recurring adjustments, necessary for a fair presentation of the accompanying balance sheets and statements of operations, changes in convertible preferred stock and stockholders’ deficit and cash flows have been made. Although these interim financial statements do not include all of the information and footnotes required for complete annual financial statements, management believes the disclosures are adequate to make the information presented not misleading. Unaudited interim results of operations and cash flows for the three and six months ended June 30, 2018 are not necessarily indicative of the results that may be expected for the full year. Unaudited interim financial statements and footnotes should be read in conjunction with the audited financial statements and footnotes included in the Company’s IPO prospectus filed with the SEC on June 29, 2018, wherein a more complete discussion of significant accounting policies and certain other information can be found.

Use of Estimates

The preparation of financial statements in accordance with GAAP and the rules and regulations of the SEC requires the use of estimates and assumptions, based on judgments considered reasonable, which affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. The Company bases its estimates and assumptions on historical experience, known trends and events and various other factors that management believes to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying value of assets and liabilities that are not readily apparent from other sources. Although management believes its estimates and assumptions are reasonable when made, they are based upon information available at the time they are made. Management evaluates the estimates and assumptions on an ongoing basis and, if necessary, makes adjustments. Due to the risks and uncertainties involved in the Company’s business and evolving market conditions, and given the subjective element of the estimates and assumptions made, actual results may differ from estimated results. The most significant estimates and judgments impact share-based compensation, product warranty accruals and the net realizable value of inventory.

Recapitalization

The Company effected a 0.0345-for-1 reverse split of its common stock on June 14, 2018. The reverse split combined each approximately 29 shares of the Company’s issued and outstanding common stock into one share of common stock and correspondingly adjusted the conversion price of its outstanding convertible preferred stock. No fractional shares were issued in connection with the reverse split. Any fractional share resulting from the reverse split was rounded down to the nearest whole share, and in lieu of any fractional share, the Company will pay in cash to the holders of such fractional shares an amount equal to the fair market value, as determined by the board of directors, of such fractional shares. All share, per share and related information presented in these interim financial statements and the related notes thereto have been retroactively adjusted, where applicable, to reflect the reverse stock split.

Summary of Significant Accounting Policies

6 Months Ended

Jun. 30, 2018

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

3.	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

The Company’s complete summary of significant accounting policies can be found in “Note 3. Summary of Significant Accounting Policies” in the audited financial statements included in the Company’s IPO prospectus filed with the SEC on June 29, 2018.

Recent Accounting Pronouncements

6 Months Ended

Jun. 30, 2018

New Accounting Pronouncements And Changes In Accounting Principles [Abstract]

Recent Accounting Pronouncements

4.	RECENT ACCOUNTING PRONOUNCEMENTS

JOBS Act Accounting Election

The Company is an emerging growth company, as defined in the Jumpstart Our Business Startups Act of 2012, or the JOBS Act. Under the JOBS Act, emerging growth companies can delay adopting new or revised accounting standards issued subsequent to the enactment of the JOBS Act until such time as those standards apply to private companies. The Company has elected to use this extended transition period for complying with new or revised accounting standards that have different effective dates for public and private companies until the earlier of the date that it (i) is no longer an emerging growth company or (ii) affirmatively and irrevocably opts out of the extended transition period provided in the JOBS Act. As a result, these interim financial statements may not be comparable to companies that comply with the new or revised accounting pronouncements as of public company effective dates.

In May 2014, the FASB issued ASU 2014-09, “Revenue from Contracts with Customers” (Topic 606), regarding the accounting for and disclosures of revenue recognition, with an effective date for public companies of annual and interim periods beginning after December 15, 2016. In July 2015, the FASB issued ASU 2015-14, “Revenue from Contracts with Customers (Topic 606): Deferral of the Effective Date,” which deferred the effective date of the previously issued revenue recognition guidance by one year. This guidance is effective for public companies for annual and interim periods beginning after December 15, 2017. For all other entities, including emerging growth companies, this standard is effective for annual reporting periods beginning after December 15, 2018, and interim periods with annual periods beginning after December 15, 2019. Early adoption is permitted. This update provides a single comprehensive model for accounting for revenue from contracts with customers. The model requires that revenue recognized reflects the actual consideration to which the entity expects to be entitled in exchange for the goods or services defined in the contract, including in situations with multiple performance obligations. In April 2016 and May 2016, the FASB issued ASU 2016-10, “Revenue from Contracts with Customers (Topic 606): Identifying Performance Obligations and Licensing” and ASU 2016-12, “Revenue from Contracts with Customers (Topic 606): Narrow-Scope Improvements and Practical Expedients,” respectively. Both of these updates provide improvements and clarification to the previously issued revenue recognition guidance. The new standard can be adopted using one of two methods: the full retrospective method, which requires the standard to be applied to each prior period presented, or the modified retrospective method, which requires the cumulative effect of adoption to be recognized as an adjustment to opening retained earnings in the period of adoption. The new standard will result in additional revenue-related disclosures in the notes to the Company’s financial statements. The majority of the Company’s revenue relates to the sales of NeuroStar Advanced Therapy Systems and treatment sessions to various customers. While the Company is still analyzing the impact of ASU 2014-09 on its financial statements and disclosures, it currently anticipates no significant changes to its revenue recognition practices as a result of the adoption of Topic 606. However, the Company currently expects the adoption of Topic 606 to change the accounting treatment for sales commissions and is analyzing the impact such change will have on its financial statements and disclosures. The Company historically expensed sales commissions as incurred. In addition, the new standard will require changes to the Company’s processes and controls to support additional disclosures, and the Company is in the process of identifying and designing such changes to processes and controls to ensure readiness.

In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842), with guidance regarding the accounting for and disclosure of leases. The update requires lessees to recognize all leases, including operating leases, with a term greater than 12 months on the balance sheet. This update also requires lessees and lessors to disclose key information about their leasing transactions. This guidance will be effective for public companies for annual and interim periods beginning after December 15, 2018. For all other entities, including emerging growth companies, this standard will be effective for annual reporting periods beginning after December 15, 2019, and interim periods within annual periods beginning after December 15, 2020. Early adoption is permitted. The Company is currently evaluating the effect that this guidance will have on its financial statements and related disclosures. The Company expects the implementation of this standard to have an impact on its financial statements and related disclosures as its aggregate future minimum lease payments under its current non-cancelable off lease were $1.4 million as of June 30, 2018, with an expiration date in 2021. The Company anticipates recognition on its balance sheet of an additional asset and corresponding liability related to this office lease. The Company is currently evaluating the impact the new standard may have on other types of leasing arrangements.

In June 2018, the FASB issued ASU 2018-07, Compensation—Stock Compensation (Topic 718): “Improvements to Nonemployee Share-Based Payment Accounting,” which largely aligns the accounting for share-based payment awards issued to nonemployees with the accounting for share-based payment awards issued to employees. Under previous GAAP, the accounting for nonemployee share-based payments differed from that applied to employee awards, particularly with regard to the measurement date and the impact of performance conditions. Under the new guidance, (i) equity-classified share-based payment awards issued to nonemployees will be measured at the grant date, instead of the previous requirement to remeasure the awards through the performance completion date, (ii) for performance conditions, compensation cost associated with the award will be recognized when the achievement of the performance condition is probable, rather than upon achievement of the performance condition, and (iii) the current requirement to reassess the classification (equity or liability) for nonemployee awards upon vesting will be eliminated, except for awards in the form of convertible instruments. This new guidance will be effective for public companies for fiscal years beginning after December 15, 2018, including interim periods within that fiscal year. Early adoption is permitted, but no earlier than an entity’s adoption date of Topic 606. The Company currently has no outstanding nonemployee share-based payment awards for which there is unrecognized compensation expense and therefore does not currently expect the adoption of the new guidance to have an effect on its financial statements.

Fair Value Measurement and Financial Instruments

6 Months Ended

Jun. 30, 2018

Fair Value Disclosures [Abstract]

Fair Value Measurement and Financial Instruments

5.	FAIR VALUE MEASUREMENT AND FINANCIAL INSTRUMENTS

The carrying values of cash equivalents, accounts receivable, prepaids and other current assets, and accounts payable on the Company’s balance sheets approximated their fair values as of June 30, 2018 and December 31, 2017 due to their short-term nature. The carrying values of the Company’s current credit facility approximated its fair value as of June 30, 2018 and December 31, 2017 due to its variable interest rate.

Certain of the Company’s financial instruments are measured at fair value using a three-level hierarchy that prioritizes the inputs used to measure fair value. This hierarchy maximizes the use of observable inputs and minimizes the use of unobservable inputs. The three levels of inputs used to measure fair value are as follows:

Level 1:	Inputs are quoted prices for identical instruments in active markets.

Level 2:	Inputs are quoted prices for similar instruments in active markets; quoted prices for identical or similar instruments in markets that are not active; or model-derived valuations whose inputs are observable or whose significant value drivers are observable.

Level 3:	Inputs are unobservable and reflect the Company’s own assumptions, based on the best information available, including the Company’s own data.

The following tables set forth the carrying amounts and fair values of the Company’s financial instruments as of June 30, 2018 and December 31, 2017 (in thousands):

	June 30, 2018
					Fair Value Measurement Based on
	Carrying Amount		Fair Value		Quoted Prices In Active Markets (Level 1)		Significant other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Assets
Money market funds (cash equivalents)	$	11,229	$	11,229	$	11,229	$	-	$	-
Liabilities
Convertible preferred stock warrant liability	$	1,893	$	1,893	$	-	$	-	$	1,893

	December 31, 2017
					Fair Value Measurement Based on
	Carrying Amount		Fair Value		Quoted Prices In Active Markets (Level 1)		Significant other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Assets
Money market funds (cash equivalents)	$	11,149	$	11,149	$	11,149	$	-	$	-
Liabilities
Convertible preferred stock warrant liability	$	478	$	478	$	-	$	-	$	478

The fair value of the convertible preferred stock warrant liability was estimated using the Black-Scholes option pricing model and the following inputs and assumptions as of June 30, 2018 and December 31, 2017:

	June 30, 2018		December 31, 2017
	Series E	Series F	Series E	Series F
Estimated fair value of convertible preferred stock	$0.92	$0.92	$0.33	$0.38
Exercise price	$0.6746	$0.3356	$0.6746	$0.3356
Remaining term (in years)	4.5	2.6 - 6.5	5.0	3.1 - 7.0
Risk-free interest rate	2.7%	2.6% - 2.8%	2.2%	2.0% - 2.3%
Expected volatility	43%	43%	43%	43% - 44%
Dividend yield	0%	0%	0%	0%

The following table presents the changes in Level 3 instruments measured on a recurring basis for the six months ended June 30, 2018 (in thousands):

Balance at December 31, 2017	$	478
Change in fair value		1,415
Balance at June 30, 2018	$	1,893

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Accounts Receivable

6 Months Ended

Jun. 30, 2018

Receivables [Abstract]

Accounts Receivable

6.	ACCOUNTS RECEIVABLE

The following table presents the composition of accounts receivable, net as of June 30, 2018 and December 31, 2017 (in thousands):

	June 30, 2018			December 31, 2017
Gross accounts receivable - trade	$	5,149		$	4,684
Less: Allowances for doubtful accounts		(425	)		(417	)
Accounts receivable, net	$	4,724		$	4,267

- Definition

The entire disclosure for claims held for amounts due a entity, excluding financing receivables. Examples include, but are not limited to, trade accounts receivables, notes receivables, loans receivables. Includes disclosure for allowance for credit losses.

+ References + Details

Property and Equipment

6 Months Ended

Jun. 30, 2018

Property Plant And Equipment [Abstract]

Property and Equipment

7.	PROPERTY AND EQUIPMENT

The following table presents the composition of property and equipment, net as of June 30, 2018 and December 31, 2017 (in thousands):

	June 30, 2018			December 31, 2017
Laboratory equipment	$	150		$	150
Office equipment		493			487
Computer equipment and software		874			680
Manufacturing equipment		273			273
Leasehold improvements		172			153
Rental equipment		1,459			1,447
Property and equipment, gross		3,421			3,190
Less: Accumulated depreciation		(1,928	)		(1,831	)
Property and equipment, net	$	1,493		$	1,359

Depreciation expense was $0.3 million and $0.1 million for the three months ended June 30, 2018 and 2017, respectively, and $0.5 million and $0.3 million for the six months ended June 30, 2018 and 2017, respectively.

Accrued Expenses

6 Months Ended

Jun. 30, 2018

Payables And Accruals [Abstract]

Accrued expenses

8.	ACCRUED EXPENSES

The following table presents the composition of accrued expenses as of June 30, 2018 and December 31, 2017 (in thousands):

	June 30, 2018		December 31, 2017
Compensation and related benefits	$	2,642	$	4,465
Consulting and professional fees		2,701		461
Research and development expenses		303		497
Sales and marketing expenses		156		620
Warranty		653		570
Sales tax payable		331		322
Interest payable		235		188
Other		710		388
Accrued expenses	$	7,731	$	7,511

Debt

6 Months Ended

Jun. 30, 2018

Debt Disclosure [Abstract]

Debt

DEBT

The following table presents the composition of debt as of June 30, 2018 and December 31, 2017 (in thousands):

	June 30, 2018			December 31, 2017
Outstanding principal	$	30,000		$	30,000
Accrued final payment fees		1,286			940
Less debt discounts		(1,289	)		(1,384	)
Total long-term debt, net		29,997			29,556
Less current portion of long-term debt		(2,500	)		-
Long-term debt, net	$	27,497		$	29,556

For the three months ended June 30, 2018, the Company recognized interest expense of $0.9 million, of which $0.7 million was cash and $0.2 million was non-cash interest expense related to the amortization of deferred debt issuance costs and accrual of final payment fees. For the three months ended June 30, 2017, the Company recognized interest expense of $0.7 million, of which $0.5 million was cash and $0.2 million was non-cash interest expense related to the amortization of deferred debt issuance costs and accrual of final payment fees.

For the six months ended June 30, 2018, the Company recognized interest expense of $1.8 million, of which $1.4 million was cash and $0.4 million was non-cash interest expense related to the amortization of deferred debt issuance costs and accrual of final payment fees. For the six months ended June 30, 2017, the Company recognized interest expense of $1.3 million, of which $1.0 million was cash and $0.3 million was non-cash interest expense related to the amortization of deferred debt issuance costs and accrual of final payment fees.

Current $35.0 Million Credit Facility

In March 2017, the Company entered into a new loan and security agreement with Oxford Finance LLC, or Oxford, for a credit facility that replaced its previous $25.0 million credit facility with Oxford and which allows it to borrow up to $35.0 million in three tranches of term loans: a Term A Loan in the amount of $25.0 million, which was drawn down immediately upon closing in March 2017, a Term B Loan in the amount of $5.0 million, which was drawn down in December 2017, and a Term C Loan in the amount of $5.0 million, which became available to the Company upon the achievement of $45.0 million of trailing twelve month revenues during the second quarter of 2018. Upon achieving the required revenue milestone, the Company had 60 days to notify its lender if it elected to borrow the Term C Loan. As a result of completing its IPO on July 2, 2018 and receiving net proceeds of $100.0 million, the Company elected not to borrow the additional $5.0 million. Each term loan accrues interest from the date of borrowing through the date of repayment at a floating per annum rate of interest, which resets monthly and is equal to the greater of (a) 8.15% or (b) the 30 day U.S. LIBOR on the last business day of the month plus 7.38%. The Company was also required to issue to Oxford at the date of each borrowing warrants to purchase its Series F or later series of convertible preferred stock with a seven year term and in an amount equal to 3.95% of the first $5.0 million of each tranche borrowed. The credit facility matures and all amounts borrowed thereunder are due on March 1, 2022. As of June 30, 2018, the Company had borrowed and had outstanding an aggregate of $30.0 million of principal under the credit facility.

The Term A Loan features an interest-only period through March 2019, during which time the Company is required to make monthly interest payments, after which time the Company is required to make monthly payments of principal and interest based on a 36-month amortization schedule. However, upon the achievement of $45.0 million of revenues during fiscal 2018, the interest-only period can be extended for an additional 12 months through March 2020 and the amortization period then becomes 24 months. In connection with the drawdown of the Term A Loan, the Company issued to the lender warrants to purchase 588,498 shares of its Series F convertible preferred stock, which had an exercise price of $0.3356 per share and which expire in March 2024. These convertible preferred stock warrants converted into common stock warrants immediately prior to the closing of the Company’s IPO on July 2, 2018.

The Term B Loan features an interest-only period through March 2019, during which time the Company is required to make monthly interest payments, after which time the Company is required to make monthly payments of principal and interest based on a 36-month amortization schedule. However, upon the achievement of $45.0 million of revenues during fiscal 2018, the interest-only period can be extended for an additional 12 months through March 2020 and the amortization period then becomes 24 months. In connection with the drawdown of the Term B Loan, the Company issued to the lender warrants to purchase 588,498 shares of its Series F convertible preferred stock, which had an exercise price of $0.3356 per share and which expire in December 2024. These convertible preferred stock warrants converted into common stock warrants immediately prior to the closing of the Company’s IPO on July 2, 2018.

In addition to principal and interest payments due under the credit facility, the Company is required to make final payment fees to the lender due upon the earlier of prepayment or maturity of each tranche, which are equal to 8% and 7% of the principal amounts of the Term A and Term B Loans, respectively, except that if the interest-only periods on the Term A and Term B Loans are extended then the final payment fees increase to 8.5% and 7.5% of the principal amounts of the Term A and Term B Loans, respectively. The Company accrues the estimated final payment fees using the effective interest rate, with a charge to non-cash interest expense, over the term of borrowing for each tranche. As of both June 30, 2018 and December 31, 2017, the effective interest rates for the Term A and Term B Loans were 10.7% and 11.6%, respectively. If the Company prepays its term loans prior to their respective scheduled maturities, it will also be required to make prepayment fees to the lender equal to 3% if prepaid on or before the first anniversary of funding, 2% if prepaid after the first and on or before the second anniversary of funding or 1% if prepaid after the second anniversary of funding of the principal amounts borrowed.

The Company’s obligations under the credit facility are secured by a first priority security interest in substantially all of its assets, other than its intellectual property. The Company has agreed not to pledge or otherwise encumber any of its intellectual property. The loan and security agreement related to the credit facility includes a financial maintenance covenant that requires the Company to achieve at least 75% of its trailing 12-month forecasted revenues, as measured each month in accordance with a forecast that the Company provided to Oxford upon signing the agreement and future forecasts that the Company is required to deliver to the lenders each year for the life of the credit facility, as well as customary affirmative and negative covenants. The Company was in compliance with all of the covenants under its credit facility as of June 30, 2018.

The loan and security agreement related to the credit facility contains events of default, including, without limitation, events of default upon: (i) failure to make payment pursuant to the terms of the agreement; (ii) violation of covenants; (iii) material adverse changes to the Company’s business; (iv) attachment or levy on the Company’s assets or judicial restraint on its business; (v) insolvency; (vi) significant judgments, orders or decrees for payments by the Company not covered by insurance; (vii) incorrectness of representations and warranties; (viii) incurrence of subordinated debt; (ix) revocation of governmental approvals necessary for the Company to conduct its business; and (x) failure by the Company to maintain a valid and perfected lien on the collateral securing the borrowing.

Based on a 36-month amortization of the outstanding principal amounts of the Term A and Term B Loans beginning on April 1, 2019 as discussed above, the following table sets forth by year the Company’s required future principal payments (in thousands):

Year:	Principal Payments
2018	$	-
2019		7,500
2020		10,000
2021		10,000
2022		2,500
Total principal payments	$	30,000

Previous $25.0 Million Credit Facility

Prior to March 2017, the Company had a $25.0 million credit facility in place with Oxford, which it entered into in February 2014 and which allowed it to borrow up to $25.0 million in three tranches of term loans: a Term A Loan in the amount of $15.0 million, a Term B Loan in the amount of $5.0 million and a Term C Loan in the amount of $5.0 million, which was never drawn down. Each term loan accrued interest at per annum rates ranging from 8.5% to 8.9%. This facility featured an interest-only period on all tranches through March 2017, and the Company was also required to issue convertible preferred stock warrants to the lender at the time of borrowing of each tranche. These convertible preferred stock warrants converted into common stock warrants immediately prior to the closing of the Company’s IPO on July 2, 2018.

In addition to principal and interest payments due under the previous $25.0 million credit facility, the Company was required to make final payment fees to the lender upon the earlier of prepayment or maturity and equal to 8.5% and 4.7% of the principal amounts of the Term A and Term B Loans, respectively. The Company accrued final payment fees using the effective interest rate, with a charge to non-cash interest expense, over the term of borrowing and until its entry into the current credit facility in March 2017, at which time the Company paid the lender $1.0 million in satisfaction of all final payment fee liabilities due under the prior credit facility.

Management evaluated whether the current credit facility entered into in March 2017 represented a debt modification or extinguishment in accordance with ASC 470-50, Debt—Modifications and Extinguishments. Upon determining that the change in cash flows between the previous and current credit facilities was not greater than 10%, management accounted for the transaction as a debt modification. As of March 2017, the unamortized balance of deferred debt issuance costs incurred in connection with the $25.0 million credit facility, and certain additional deferred debt issuance costs incurred in connection with entry into the current credit facility, are being amortized to interest expense through March 2022 utilizing the effective interest method.

Convertible Preferred Stock and Stockholders’ Deficit

6 Months Ended

Jun. 30, 2018

Equity [Abstract]

Convertible Preferred Stock and Stockholders’ Deficit

10.	CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS’ DEFICIT

Initial Public Offering

On July 2, 2018, the Company closed its IPO, in which the Company issued and sold 6.325 million shares of its common stock, which included the exercise of the underwriters’ option to purchase an additional 0.825 million shares of common stock, at a public offering price of $17.00 per share. The Company received net proceeds of $100.0 million after deducting underwriting discounts and commissions of $7.5 million but before deducting other offering expenses. In addition, upon the closing of the IPO on July 2, 2018, (i) all of the Company’s outstanding shares of convertible preferred stock converted into 11.0 million shares of common stock; (ii) all of the Company’s outstanding warrants to purchase convertible preferred stock converted into warrants to purchase common stock; and (iii) the Company filed an amended and restated certificate of incorporation to, among other things, decrease the number of shares of common stock, $0.01 par value per share, authorized for issuance to 200.0 million and to authorize the board of directors to issue up to 10.0 million shares of “blank check” preferred stock, $0.01 par value per share.

Common Stock

The Company’s amended certificate of incorporation as of June 30, 2018 authorized the issuance of 413.9 million shares of common stock, $0.01 par value per share, of which 0.3 million were issued and outstanding as of June 30, 2018. In addition, the Company was required to reserve and keep available out of its authorized but unissued shares of common stock a number of shares sufficient to effect the conversion into common stock of all outstanding shares of convertible preferred stock and convertible preferred stock warrants, convertible preferred stock or common stock warrants issuable upon borrowing the Term C Loan under the current $35.0 million credit facility, stock options granted and shares available for grant under its stock incentive plan.

The following table summarizes the total number of shares of the Company’s common stock issued and reserved for issuance as of June 30, 2018 (in thousands):

	June 30, 2018
Shares of common stock issued		257
Shares of common stock reserved for issuance for:
Convertible preferred stock outstanding:
Series A-1		166
Series A-2 ⁽¹⁾		898
Series B ⁽²⁾		697
Series C ⁽³⁾		1,063
Series D		1,705
Series E		1,534
Series F		3,531
Series G		1,400
Convertible preferred stock warrants outstanding:
Series E		14
Series F		91
Warrants issuable upon Term C Loan borrowing		20
Stock options outstanding		2,855
Shares available for grant under stock incentive plan		48
Total shares of common stock issued and reserved for issuance		14,279

___________________________

⁽¹⁾	Shares of Series A-2 convertible preferred stock convert to common stock at a ratio of 0.03539 shares of common stock per share of Series A-2 convertible preferred stock.

⁽²⁾	Shares of Series B convertible preferred stock convert to common stock at a ratio of 0.04103 shares of common stock per share of Series B convertible preferred stock.

⁽³⁾	Shares of Series C convertible preferred stock convert to common stock at a ratio of 0.05071 shares of common stock per share of Series C convertible preferred stock.

Each share of common stock entitles the holder to one vote on all matters submitted to a vote of the Company’s stockholders. Subject to preferences that may apply to any outstanding convertible preferred stock, holders of common stock are entitled to receive proportionally any dividends that the Company’s board of directors may declare out of funds legally available for that purpose on a non-cumulative basis. The Company has never paid, and for the foreseeable future does not expect to pay, a dividend on its common stock.

Convertible Preferred Stock

The Company’s amended certificate of incorporation as of June 30, 2018 authorized the issuance of 308.6 million shares of convertible preferred stock, $0.01 par value per share, of which the Company had designated and issued Series A-1, Series A-2, Series B, Series C, Series D, Series E, Series F and Series G shares. Series A-1 through Series E shares of convertible preferred stock are referred to collectively as Junior Securities and are subordinate to shares of Series G and Series F convertible preferred stock. All of the Company’s convertible preferred stock was classified outside of stockholders’ deficit as of June 30, 2018 because the shares contain deemed liquidation rights that are a contingent redemption feature not solely within the control of the Company and the IPO had not yet closed.

The following table summarizes the Company’s outstanding convertible preferred stock as of June 30, 2018 and December 31, 2017:

	Shares Authorized and Designated (in thousands)		Shares Issued and Outstanding (in thousands)		Carrying Value (in thousands)		Liquidation Value per Share		Liquidation Value (in thousands)
Series A-1		4,800		4,800	$	900	$	0.0617	$	296
Series A-2		25,385		25,385		16,428	$	0.2052		5,209
Series B		17,000		17,000		16,859	$	0.3168		5,386
Series C		20,958		20,958		34,841	$	0.5253		11,009
Series D		49,426		49,426		29,970	$	0.2874		14,205
Series E		44,873		44,471		29,800	$	0.5144		22,876
Series F		105,567		102,334		43,513	$	0.3356		34,343
Series G		40,584		40,584		14,825	$	0.3696		15,000
Balance at June 30, 2018 and December 31, 2017		308,593		304,958	$	187,136			$	108,324

Conversion

Each share and series of convertible preferred stock is convertible into common stock at any time at the option of the holder thereof at the conversion price then in effect (each subject to adjustments upon the occurrence of certain dilutive events). At June 30, 2018 and immediately prior to the closing of the Company’s IPO on July 2, 2018, the conversion price for Series A-1, Series D, Series E, Series F and Series G shares was equal to the original issue price, resulting in a common stock conversion ratio of 1:0.0345. At June 30, 2018 and immediately prior to the closing of the Company’s IPO on July 2, 2018, as a result of past anti-dilution adjustments, the conversion price for Series A-2, Series B and Series C shares was below the original issue price, resulting in common stock conversion ratios of 1:0.03539, 1:0.04103 and 1:0.05071, respectively. Immediately prior to the closing of the Company’s IPO on July 2, 2018, all of the Company’s outstanding shares of convertible preferred stock converted into 11.0 million shares of common stock.

Liquidation Preferences

As of June 30, 2018

In the event of a liquidation, dissolution or winding up of the Company, either voluntary or involuntary, or in the event of a deemed liquidation event, which includes a sale of the Company as defined in the Company’s certificate of incorporation, holders of Series G convertible preferred stock were entitled to receive, in preference to all other stockholders, an amount equal to their original investment amount plus any declared and unpaid dividends. If upon the occurrence of such event the assets and funds available for distribution are insufficient to pay such holders the full amount to which they are entitled, then the entire assets and funds legally available for distribution shall be distributed ratably among the holders of the Series G convertible preferred stock in proportion to the full amounts to which they would otherwise be entitled.

After payment in full of the liquidation preference of the Series G convertible preferred stock, holders of Series F convertible preferred stock were entitled to receive, in preference to all holders of Junior Securities and common stock, an amount equal to their original investment amount plus any declared and unpaid dividends. If upon the occurrence of such event the assets and funds available for distribution are insufficient to pay such holders the full amount to which they are entitled, then the entire remaining assets and funds legally available for distribution shall be distributed ratably among the holders of the Series F convertible preferred stock in proportion to the full amounts to which they would otherwise be entitled.

After payment in full of the liquidation preferences of the Series G and Series F convertible preferred stock, holders of Junior Securities were entitled to receive an amount equal to $59.2 million in the aggregate. If upon the occurrence of such event the assets and funds available for distribution are insufficient to pay such holders the full amount to which they are entitled, then the entire assets and funds legally available for distribution shall be distributed ratably among the holders of the Junior Securities in proportion to the full amounts to which they would otherwise be entitled.

After payment in full of the liquidation preferences of the Series G, Series F and Junior Securities convertible preferred stock, holders of Series F convertible preferred stock were entitled to receive an additional liquidation preference at an amount equal to $0.1678 per share. If upon the occurrence of such event the assets and funds available for distribution are insufficient to pay such holders the full amount to which they are entitled, then the entire assets and funds legally available for distribution shall be distributed ratably among the holders of the Series F convertible preferred stock in proportion to the full amounts to which they would otherwise be entitled.

After payment in full of the liquidation preferences of the Series G, Series F and Junior Securities convertible preferred stock and the additional liquidation preference for holders of Series F convertible preferred stock, holders of common stock and holders of Junior Securities, Series F and Series G convertible preferred stock are entitled to receive a liquidation preference until the amount distributed to holders of the Series F convertible preferred stock equals $1.0068 plus declared but unpaid dividends on each share and then to the holders of common stock and holders of Junior Securities and Series G convertible preferred stock until the aggregate amount distributed to such holders equals the amount distributed to holders of Series F convertible preferred stock divided by the Series F ownership percentage.

After payments of the above liquidation preferences have been made, any remaining assets shall be distributed ratably to holders of common stock and holders of Series G, Series F and Junior Securities convertible preferred stock on an “as-converted” basis.

As of July 2, 2018

Immediately prior to the closing of the Company’s IPO on July 2, 2018, all of the Company’s outstanding shares of convertible preferred stock converted into 11.0 million shares of common stock, resulting in the elimination of the Company’s outstanding liquidation preferences.

Dividends

Each class of convertible preferred stock was entitled to receive non-cumulative annual dividends at a rate of 9.0%, if and when declared by the Company’s board of directors. The holders of Series G convertible preferred stock were entitled to dividends in preference to holders of any other class or series of the Company’s stock. The holders of Series F convertible preferred stock were entitled to dividends in preference to all holders of Junior Securities and holders of common stock. The holders of Junior Securities were entitled to dividends in preference to holders of common stock.

In the event a dividend is declared to common stockholders, holders of each class of convertible preferred stock will also receive an equivalent dividend on an “as-converted” basis. The Company has never paid, and for the foreseeable future does not expect to pay, a dividend on its common stock.

Voting

The holders of each class of convertible preferred stock were entitled to one vote for each share of common stock into which their shares of convertible preferred stock may be converted and, subject to certain convertible preferred stock class votes specified in the Company’s certificate of incorporation or as required by law, the holders of convertible preferred stock and common stock vote together on an “as-converted” basis.

Convertible Preferred Stock Warrants

The following table summarizes the Company’s outstanding convertible preferred stock warrants as of June 30, 2018:

	Warrants Outstanding (in thousands)		Exercise Price		Expiration Date
Series E		402	$	0.6746	Dec-2022
Series F		878	$	0.3356	Feb-2021
Series F		589	$	0.3356	Aug-2023
Series F		589	$	0.3356	Mar-2024
Series F		588	$	0.3356	Dec-2024
		3,046

Immediately prior to the closing of the Company’s IPO on July 2, 2018, all of the Company’s outstanding convertible preferred stock warrants converted into 0.1 million common stock warrants.

Loss Per Share

6 Months Ended

Jun. 30, 2018

Earnings Per Share [Abstract]

Loss Per Share

11.	LOSS PER SHARE

The Company’s basic loss per common share is computed by dividing the net loss by the weighted-average number of shares of common stock outstanding during the period. The Company’s restricted stock awards (non-vested shares) are issued and outstanding at the time of grant but are excluded from the Company’s computation of weighted-average shares outstanding in the determination of basic loss per share until vesting occurs.

A net loss cannot be diluted, so when the Company is in a net loss position, basic and diluted loss per common share are the same. If in the future the Company achieves profitability, the denominator of a diluted earnings per common share calculation will include both the weighted-average number of shares outstanding and the number of common stock equivalents, if the inclusion of such common stock equivalents would be dilutive. Dilutive common stock equivalents potentially include warrants, stock options and non-vested restricted stock awards using the treasury stock method, along with the effect, if any, from the potential conversion of outstanding securities, such as convertible preferred stock.

The following potentially dilutive securities outstanding as of June 30, 2018 and 2017 have been excluded from the denominator of the diluted loss per share of common stock outstanding calculation (in thousands):

	June 30,
	2018		2017
Stock options		2,855		2,076
Non-vested restricted stock awards		10		17
Convertible preferred stock warrants		105		85
Shares of convertible preferred stock “as-converted”		10,994		10,994

Share-based Compensation

6 Months Ended

Jun. 30, 2018

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Share-based Compensation

12.	SHARE-BASED COMPENSATION

The amount of share-based compensation expense recognized by the Company by location in its statements of operations for the three and six months ended June 30, 2018 and 2017 is as follows (in thousands):

	Three Months ended June 30,				Six Months ended June 30,
	2018		2017		2018		2017
Cost of revenues	$	5	$	7	$	9	$	7
Sales and marketing		65		43		119		56
General and administrative		87		92		142		108
Research and development		35		14		66		27
Total	$	192	$	156	$	336	$	198

2003 Stock Incentive Plan

In April 2003 (and as subsequently amended), the Company adopted the 2003 Stock Incentive Plan, or 2003 Plan, which authorized the issuance of up to 3.1 million shares in the form of restricted stock, stock appreciation rights and stock options to the Company’s directors, employees and consultants. The amount and terms of grants are determined by the Company’s board of directors. To date, the Company has granted restricted stock awards only to an independent member of its board of directors and only as compensation for board service. All stock options granted to date have had exercise prices equal to the estimated fair value, as determined by the board of directors, of the underlying common stock on the date of the grant. The contractual term of stock options is up to 10 years, and stock options are exercisable in cash or as otherwise determined by the board of directors. Generally, stock options vest 25% upon the first anniversary of the date of grant and the remainder ratably monthly thereafter for 36 months. As of June 30, 2018, there were 0.05 million shares available for future issuance under the 2003 Plan. As of the closing of the Company’s IPO, all shares available for issuance under the 2003 Plan were carried over to the newly adopted 2018 Stock Incentive Plan, or 2018 Plan. Therefore, the Company will not issue any additional equity awards under the 2003 Plan.

Stock Options

The following table summarizes the Company’s stock option activity for the six months ended June 30, 2018:

	Number of Shares under Option (in thousands)			Weighted- average Exercise Price per Option		Weighted- average Remaining Contractual Life (in years)		Aggregate Intrinsic Value (in thousands)
Outstanding at December 31, 2017		2,444		$	2.39
Granted		502		$	5.94
Exercised		(26	)	$	1.43
Forfeited		(65	)	$	3.20
Outstanding at June 30, 2018		2,855		$	3.00		7.6	$	67,395
Exercisable at June 30, 2018		1,426		$	2.22		6.3	$	34,779
Vested and expected to vest at June 30, 2018		2,855		$	3.00		7.6	$	67,395

The Company recognized share-based compensation expense related to stock options of $0.2 million and $0.2 million for the three months ended June 30, 2018 and 2017, respectively, and $0.3 million and $0.2 million for the six months ended June 30, 2018 and 2017, respectively. As of June 30, 2018, there was $2.7 million of total unrecognized compensation cost related to non-vested stock options which the Company expects to recognize over a weighted-average period of 3.2 years. The weighted-average grant-date fair value of stock options granted during the six months ended June 30, 2018 was estimated at $3.64 per option. The total intrinsic value of stock options exercised during the six months ended June 30, 2018 was $0.1 million.

For the six months ended June 30, 2018, the grant-date fair value of stock options was estimated at the time of grant using the following weighted-average inputs and assumptions in the Black-Scholes option pricing model:

Estimated fair value of common stock	$	5.94
Exercise price	$	5.94
Expected term (in years)		6.0
Risk-free interest rate		2.7	%
Expected volatility		65.8	%
Dividend yield		0	%

In April 2018, the Company’s board of directors granted options to purchase 54,794 shares of common stock to the members of the board. These options have an exercise price of $5.22 and vest in 12 equal monthly installments beginning in March 2018; however, the entire grant was subject to forfeiture if an initial public offering of the Company’s common stock did not occur by December 31, 2018. The estimated grant-date fair value of the options awards was $0.2 million. Upon the closing of the Company’s IPO on July 2, 2018, the Company will immediately recognize the fair value of the vested portion of the awards as share-based compensation expense, with the unvested portion to be recognized as share-based compensation expense ratably over the remaining service period.

Restricted Stock Awards

The following table summarizes the Company’s restricted stock award activity for the six months ended June 30, 2018:

	Non-vested Restricted Stock Awards (in thousands)			Weighted- average Grant-date Fair Value
Non-vested at December 31, 2017		16		$	2.32
Vested		(6	)	$	2.32
Non-vested at June 30, 2018		10		$	2.32

The Company recognized minimal share-based compensation expense related to restricted stock awards during the three and six months ended June 30, 2018 and 2017. As of June 30, 2018, there was minimal unrecognized compensation cost related to non-vested restricted stock awards which the Company expects to recognize over a weighted-average period of 9 months. The total fair value at the vesting date of restricted stock awards vested during the six months ended June 30, 2018 was $0.05 million.

Employee Benefit Plans

6 Months Ended

Jun. 30, 2018

Compensation And Retirement Disclosure [Abstract]

Employee Benefit Plans

13.	EMPLOYEE BENEFIT PLANS

401(k) Defined Contribution Plan

The Company maintains a 401(k) defined contribution retirement plan which covers all of its employees. Employees are eligible to participate on the first of the month following their date of hire. Under the 401(k) plan, participating employees may defer up to 100% of their pre-tax salary but not more than statutory limits. There is currently no employer matching of employee contributions and employee contributions vest immediately.

Commitments and Contingencies

6 Months Ended

Jun. 30, 2018

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingencies

14.	COMMITMENTS AND CONTINGENCIES

Executive Employment Agreements

The Company has entered into an employment agreement and offer letters with certain key executives, providing for compensation and severance in certain circumstances, as defined in the agreements.

Leases

In January 2013, the Company entered into a 93-month lease for its headquarters office and warehouse. The Company also rents certain office equipment. The Company recognizes rent expense on a straight-line basis over the lease period and has accrued for rent expense incurred but not yet paid. Landlord allowances for tenant improvements are deferred and recognized as a reduction to rent expense on a straight-line basis and over the remaining lease term.

Legal Matters

The Company is subject from time to time to various claims and legal actions arising during the ordinary course of its business. Management believes that there are currently no claims or legal actions that would reasonably be expected to have a material adverse effect on the Company’s results of operations, financial condition, or cash flows.

Geographical Segment Information

6 Months Ended

Jun. 30, 2018

Segments Geographical Areas [Abstract]

Geographical Segment Information

15.	GEOGRAPHICAL SEGMENT INFORMATION

Operating segments are defined as components of an enterprise about which separate discrete information is available for evaluation by the chief operating decision maker, or decision making group, in deciding how to allocate resources and in assessing performance. The Company currently operates in one business segment as it is managed and operated as one business. A single management team that reports to the chief operating decision maker comprehensively manages the entire business. The Company does not operate any material separate lines of business or separate business entities with respect to its products or product development.

The following geographic data includes revenue generated from the Company’s third-party distributors. The Company’s revenue was generated in the following geographic regions for the years indicated (in thousands):

	Revenues by Geography
	Three Months ended June 30,
	2018					2017
	Amount		% of Revenues			Amount		% of Revenues
United States	$	12,898		97	%	$	10,225		99	%
International		354		3	%		83		1	%
Total revenues	$	13,252		100	%	$	10,308		100	%

	Revenues by Geography
	Six Months ended June 30,
	2018					2017
	Amount		% of Revenues			Amount		% of Revenues
United States	$	22,870		98	%	$	17,619		99	%
International		534		2	%		215		1	%
Total revenues	$	23,404		100	%	$	17,834		100	%

Basis of Presentation (Policies)	6 Months Ended
Basis of Presentation (Policies)	Jun. 30, 2018
Accounting Policies [Abstract]
Interim Financial Statements	Interim Financial Statements The accompanying unaudited interim financial statements have been prepared from the books and records of the Company in accordance with GAAP for interim financial information and Rule 10-01 of Regulation S-X promulgated by the United States Securities and Exchange Commission, or SEC, which permit reduced disclosures for interim periods. All adjustments, consisting only of normal recurring adjustments, necessary for a fair presentation of the accompanying balance sheets and statements of operations, changes in convertible preferred stock and stockholders’ deficit and cash flows have been made. Although these interim financial statements do not include all of the information and footnotes required for complete annual financial statements, management believes the disclosures are adequate to make the information presented not misleading. Unaudited interim results of operations and cash flows for the three and six months ended June 30, 2018 are not necessarily indicative of the results that may be expected for the full year. Unaudited interim financial statements and footnotes should be read in conjunction with the audited financial statements and footnotes included in the Company’s IPO prospectus filed with the SEC on June 29, 2018, wherein a more complete discussion of significant accounting policies and certain other information can be found.
Use of Estimates	Use of Estimates The preparation of financial statements in accordance with GAAP and the rules and regulations of the SEC requires the use of estimates and assumptions, based on judgments considered reasonable, which affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. The Company bases its estimates and assumptions on historical experience, known trends and events and various other factors that management believes to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying value of assets and liabilities that are not readily apparent from other sources. Although management believes its estimates and assumptions are reasonable when made, they are based upon information available at the time they are made. Management evaluates the estimates and assumptions on an ongoing basis and, if necessary, makes adjustments. Due to the risks and uncertainties involved in the Company’s business and evolving market conditions, and given the subjective element of the estimates and assumptions made, actual results may differ from estimated results. The most significant estimates and judgments impact share-based compensation, product warranty accruals and the net realizable value of inventory.
Recapitalization	Recapitalization The Company effected a 0.0345-for-1 reverse split of its common stock on June 14, 2018. The reverse split combined each approximately 29 shares of the Company’s issued and outstanding common stock into one share of common stock and correspondingly adjusted the conversion price of its outstanding convertible preferred stock. No fractional shares were issued in connection with the reverse split. Any fractional share resulting from the reverse split was rounded down to the nearest whole share, and in lieu of any fractional share, the Company will pay in cash to the holders of such fractional shares an amount equal to the fair market value, as determined by the board of directors, of such fractional shares. All share, per share and related information presented in these interim financial statements and the related notes thereto have been retroactively adjusted, where applicable, to reflect the reverse stock split.

Fair Value Measurement and Financial Instruments (Tables)

6 Months Ended

Jun. 30, 2018

Fair Value Disclosures [Abstract]

Schedule of Carrying Amounts and Fair Values of Financial Instruments

The following tables set forth the carrying amounts and fair values of the Company’s financial instruments as of June 30, 2018 and December 31, 2017 (in thousands):

	June 30, 2018
					Fair Value Measurement Based on
	Carrying Amount		Fair Value		Quoted Prices In Active Markets (Level 1)		Significant other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Assets
Money market funds (cash equivalents)	$	11,229	$	11,229	$	11,229	$	-	$	-
Liabilities
Convertible preferred stock warrant liability	$	1,893	$	1,893	$	-	$	-	$	1,893

	December 31, 2017
					Fair Value Measurement Based on
	Carrying Amount		Fair Value		Quoted Prices In Active Markets (Level 1)		Significant other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Assets
Money market funds (cash equivalents)	$	11,149	$	11,149	$	11,149	$	-	$	-
Liabilities
Convertible preferred stock warrant liability	$	478	$	478	$	-	$	-	$	478

Summary of Fair Value Inputs and Assumptions

	June 30, 2018		December 31, 2017
	Series E	Series F	Series E	Series F
Estimated fair value of convertible preferred stock	$0.92	$0.92	$0.33	$0.38
Exercise price	$0.6746	$0.3356	$0.6746	$0.3356
Remaining term (in years)	4.5	2.6 - 6.5	5.0	3.1 - 7.0
Risk-free interest rate	2.7%	2.6% - 2.8%	2.2%	2.0% - 2.3%
Expected volatility	43%	43%	43%	43% - 44%
Dividend yield	0%	0%	0%	0%

Summary of Changes in Instruments Measured on Recurring Basis

The following table presents the changes in Level 3 instruments measured on a recurring basis for the six months ended June 30, 2018 (in thousands):

Balance at December 31, 2017	$	478
Change in fair value		1,415
Balance at June 30, 2018	$	1,893

Accounts Receivable (Tables)

6 Months Ended

Jun. 30, 2018

Receivables [Abstract]

Composition of Accounts Receivable, Net

The following table presents the composition of accounts receivable, net as of June 30, 2018 and December 31, 2017 (in thousands):

	June 30, 2018			December 31, 2017
Gross accounts receivable - trade	$	5,149		$	4,684
Less: Allowances for doubtful accounts		(425	)		(417	)
Accounts receivable, net	$	4,724		$	4,267

Property and Equipment (Tables)

6 Months Ended

Jun. 30, 2018

Property Plant And Equipment [Abstract]

Summary of Composition of Property and Equipment, Net

The following table presents the composition of property and equipment, net as of June 30, 2018 and December 31, 2017 (in thousands):

	June 30, 2018			December 31, 2017
Laboratory equipment	$	150		$	150
Office equipment		493			487
Computer equipment and software		874			680
Manufacturing equipment		273			273
Leasehold improvements		172			153
Rental equipment		1,459			1,447
Property and equipment, gross		3,421			3,190
Less: Accumulated depreciation		(1,928	)		(1,831	)
Property and equipment, net	$	1,493		$	1,359

Accrued Expenses (Tables)

6 Months Ended

Jun. 30, 2018

Payables And Accruals [Abstract]

Summary of Composition of Accrued Expenses

The following table presents the composition of accrued expenses as of June 30, 2018 and December 31, 2017 (in thousands):

	June 30, 2018		December 31, 2017
Compensation and related benefits	$	2,642	$	4,465
Consulting and professional fees		2,701		461
Research and development expenses		303		497
Sales and marketing expenses		156		620
Warranty		653		570
Sales tax payable		331		322
Interest payable		235		188
Other		710		388
Accrued expenses	$	7,731	$	7,511

Debt (Tables)

6 Months Ended

Jun. 30, 2018

Debt Disclosure [Abstract]

Summary of Composition of Debt

The following table presents the composition of debt as of June 30, 2018 and December 31, 2017 (in thousands):

	June 30, 2018			December 31, 2017
Outstanding principal	$	30,000		$	30,000
Accrued final payment fees		1,286			940
Less debt discounts		(1,289	)		(1,384	)
Total long-term debt, net		29,997			29,556
Less current portion of long-term debt		(2,500	)		-
Long-term debt, net	$	27,497		$	29,556

Summary of Future Principal Payments

Year:	Principal Payments
2018	$	-
2019		7,500
2020		10,000
2021		10,000
2022		2,500
Total principal payments	$	30,000

- Definition

Tabular disclosure of long-debt instruments or arrangements, including identification, terms, features, collateral requirements and other information necessary to a fair presentation. These are debt arrangements that originally required repayment more than twelve months after issuance or greater than the normal operating cycle of the entity, if longer.

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+ Details

Convertible Preferred Stock and Stockholders’ Deficit (Tables)

6 Months Ended

Jun. 30, 2018

Equity [Abstract]

Summary of Common Stock Issued and Reserved for Issuance

The following table summarizes the total number of shares of the Company’s common stock issued and reserved for issuance as of June 30, 2018 (in thousands):

	June 30, 2018
Shares of common stock issued		257
Shares of common stock reserved for issuance for:
Convertible preferred stock outstanding:
Series A-1		166
Series A-2 ⁽¹⁾		898
Series B ⁽²⁾		697
Series C ⁽³⁾		1,063
Series D		1,705
Series E		1,534
Series F		3,531
Series G		1,400
Convertible preferred stock warrants outstanding:
Series E		14
Series F		91
Warrants issuable upon Term C Loan borrowing		20
Stock options outstanding		2,855
Shares available for grant under stock incentive plan		48
Total shares of common stock issued and reserved for issuance		14,279

___________________________

⁽¹⁾	Shares of Series A-2 convertible preferred stock convert to common stock at a ratio of 0.03539 shares of common stock per share of Series A-2 convertible preferred stock.

⁽²⁾	Shares of Series B convertible preferred stock convert to common stock at a ratio of 0.04103 shares of common stock per share of Series B convertible preferred stock.

⁽³⁾	Shares of Series C convertible preferred stock convert to common stock at a ratio of 0.05071 shares of common stock per share of Series C convertible preferred stock.

Summary of Outstanding Convertible Preferred Stock

The following table summarizes the Company’s outstanding convertible preferred stock as of June 30, 2018 and December 31, 2017:

	Shares Authorized and Designated (in thousands)		Shares Issued and Outstanding (in thousands)		Carrying Value (in thousands)		Liquidation Value per Share		Liquidation Value (in thousands)
Series A-1		4,800		4,800	$	900	$	0.0617	$	296
Series A-2		25,385		25,385		16,428	$	0.2052		5,209
Series B		17,000		17,000		16,859	$	0.3168		5,386
Series C		20,958		20,958		34,841	$	0.5253		11,009
Series D		49,426		49,426		29,970	$	0.2874		14,205
Series E		44,873		44,471		29,800	$	0.5144		22,876
Series F		105,567		102,334		43,513	$	0.3356		34,343
Series G		40,584		40,584		14,825	$	0.3696		15,000
Balance at June 30, 2018 and December 31, 2017		308,593		304,958	$	187,136			$	108,324

Summary of Outstanding Convertible Preferred Stock Warrants

The following table summarizes the Company’s outstanding convertible preferred stock warrants as of June 30, 2018:

	Warrants Outstanding (in thousands)		Exercise Price		Expiration Date
Series E		402	$	0.6746	Dec-2022
Series F		878	$	0.3356	Feb-2021
Series F		589	$	0.3356	Aug-2023
Series F		589	$	0.3356	Mar-2024
Series F		588	$	0.3356	Dec-2024
		3,046

- Definition

Tabular disclosure of an entity's stock, including par or stated value per share, number and dollar amount of share subscriptions, shares authorized, shares issued, shares outstanding, number and dollar amount of shares held in an employee trust, dividend per share, total dividends, share conversion features, par value plus additional paid in capital, the value of treasury stock and other information necessary to a fair presentation, and EPS information. Stock by class includes common, convertible, and preferred stocks which are not redeemable or redeemable solely at the option of the issuer. Includes preferred stock with redemption features that are solely within the control of the issuer and mandatorily redeemable stock if redemption is required to occur only upon liquidation or termination of the reporting entity. If more than one issue is outstanding, state the title of each issue and the corresponding dollar amount; dollar amount of any shares subscribed but unissued and the deduction of subscriptions receivable there from; number of shares authorized, issued, and outstanding.

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- Definition

Tabular disclosure of warrants or rights issued. Warrants and rights outstanding are derivative securities that give the holder the right to purchase securities (usually equity) from the issuer at a specific price within a certain time frame. Warrants are often included in a new debt issue to entice investors by a higher return potential. The main difference between warrants and call options is that warrants are issued and guaranteed by the company, whereas options are exchange instruments and are not issued by the company. Also, the lifetime of a warrant is often measured in years, while the lifetime of a typical option is measured in months. Disclose the title of issue of securities called for by warrants and rights outstanding, the aggregate amount of securities called for by warrants and rights outstanding, the date from which the warrants or rights are exercisable, and the price at which the warrant or right is exercisable.

+ References + Details

Loss Per Share (Tables)

6 Months Ended

Jun. 30, 2018

Earnings Per Share [Abstract]

Schedule of Potentially Dilutive Securities Outstanding Excluded from Diluted Loss Per Share Calculation

	June 30,
	2018		2017
Stock options		2,855		2,076
Non-vested restricted stock awards		10		17
Convertible preferred stock warrants		105		85
Shares of convertible preferred stock “as-converted”		10,994		10,994

Share-Based Compensation (Tables)

6 Months Ended

Jun. 30, 2018

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Share-Based Compensation Expense

	Three Months ended June 30,				Six Months ended June 30,
	2018		2017		2018		2017
Cost of revenues	$	5	$	7	$	9	$	7
Sales and marketing		65		43		119		56
General and administrative		87		92		142		108
Research and development		35		14		66		27
Total	$	192	$	156	$	336	$	198

Summary of Stock Option Activity

The following table summarizes the Company’s stock option activity for the six months ended June 30, 2018:

	Number of Shares under Option (in thousands)			Weighted- average Exercise Price per Option		Weighted- average Remaining Contractual Life (in years)		Aggregate Intrinsic Value (in thousands)
Outstanding at December 31, 2017		2,444		$	2.39
Granted		502		$	5.94
Exercised		(26	)	$	1.43
Forfeited		(65	)	$	3.20
Outstanding at June 30, 2018		2,855		$	3.00		7.6	$	67,395
Exercisable at June 30, 2018		1,426		$	2.22		6.3	$	34,779
Vested and expected to vest at June 30, 2018		2,855		$	3.00		7.6	$	67,395

Summary of Weighted-average Inputs and Assumptions used to Estimate Grant-date Fair Value of Stock Options

Estimated fair value of common stock	$	5.94
Exercise price	$	5.94
Expected term (in years)		6.0
Risk-free interest rate		2.7	%
Expected volatility		65.8	%
Dividend yield		0	%

Summary of Restricted Stock Award Activity

The following table summarizes the Company’s restricted stock award activity for the six months ended June 30, 2018:

	Non-vested Restricted Stock Awards (in thousands)			Weighted- average Grant-date Fair Value
Non-vested at December 31, 2017		16		$	2.32
Vested		(6	)	$	2.32
Non-vested at June 30, 2018		10		$	2.32

Geographical Segment Information (Tables)

6 Months Ended

Jun. 30, 2018

Segments Geographical Areas [Abstract]

Summary of Revenue Generated in Geographic Regions for Years Indicated

	Revenues by Geography
	Three Months ended June 30,
	2018					2017
	Amount		% of Revenues			Amount		% of Revenues
United States	$	12,898		97	%	$	10,225		99	%
International		354		3	%		83		1	%
Total revenues	$	13,252		100	%	$	10,308		100	%

	Revenues by Geography
	Six Months ended June 30,
	2018					2017
	Amount		% of Revenues			Amount		% of Revenues
United States	$	22,870		98	%	$	17,619		99	%
International		534		2	%		215		1	%
Total revenues	$	23,404		100	%	$	17,834		100	%

Description of Business - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands		6 Months Ended		12 Months Ended
	Jul. 02, 2018	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Description Of Business [Line Items]
Common stock, par value per share		$ 0.01		$ 0.01
Common stock, shares authorized for issuance		413,918,000		413,918,000
Preferred stock, shares authorized for issuance		0		0
Preferred stock, par value per share		$ 0.01		$ 0.01
Cash and cash equivalents		$ 14,544	$ 26,233	$ 29,147	$ 17,040
Accumulated deficit		209,939		196,946
Cash flows from operating activities		13,397	$ 9,481	$ 11,100
$35.0 Million Credit Facility \| Oxford Finance LLC
Description Of Business [Line Items]
Borrowings outstanding under credit facility		$ 30,000
Credit facility maturity date		Mar. 01, 2022
Subsequent Event
Description Of Business [Line Items]
IPO closing date	Jul. 02, 2018
Initial Public Offering \| Subsequent Event
Description Of Business [Line Items]
Net proceeds from initial public offering	$ 100,000
Underwriting discounts and commissions before deducting offering expense	$ 7,500
Common stock, par value per share	$ 0.01
Common stock, shares authorized for issuance	200,000,000
Preferred stock, shares authorized for issuance	10,000,000
Preferred stock, par value per share	$ 0.01
Initial Public Offering \| Subsequent Event \| Common Stock
Description Of Business [Line Items]
Common stock shares issued and sold	6,325,000
Exercise of underwriter's option to purchase additional shares	825,000
Issuance price per share	$ 17.00
Convertible preferred stock converted into common stock	11,000,000

Basis of Presentation - Additional Information (Details)		6 Months Ended
	Jun. 14, 2018	Jun. 30, 2018
Accounting Policies [Abstract]
Reverse stock split description		0.0345-for-1 reverse split
Reverse stock split, Conversion ratio	0.0345

Recent Accounting Pronouncements - Additional Information (Details) $ in Millions	6 Months Ended
	Jun. 30, 2018 USD ($)
New Accounting Pronouncements And Changes In Accounting Principles [Abstract]
Aggregate future minimum lease payments	$ 1.4
Current non-cancelable office lease, expiration date	2021

Fair Value Measurement and Financial Instruments - Schedule of Carrying Amounts and Fair Values of Financial Instruments (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Carrying Amount \| Money market funds
Assets
Total assets	$ 11,229	$ 11,149
Fair Value \| Money market funds
Assets
Total assets	11,229	11,149
Convertible preferred sock warrant liability \| Carrying Amount
Liabilities
Total liabilities	1,893	478
Convertible preferred sock warrant liability \| Fair Value
Liabilities
Total liabilities	1,893	478
Quoted Prices In Active Markets (Level 1) \| Money market funds
Assets
Total assets	11,229	11,149
Significant Unobservable Inputs (Level 3) \| Convertible preferred sock warrant liability
Liabilities
Total liabilities	$ 1,893	$ 478

Fair Value Measurement and Financial Instruments - Summary of Fair Value Inputs and Assumptions (Details)	6 Months Ended	12 Months Ended
	Jun. 30, 2018 $ / shares	Dec. 31, 2017 $ / shares
Estimated Fair Value of Convertible Preferred Stock \| Series E
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Fair value assumption	0.92	0.33
Estimated Fair Value of Convertible Preferred Stock \| Series F
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Fair value assumption	0.92	0.38
Exercise Price \| Series E
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Fair value assumption	0.6746	0.6746
Exercise Price \| Series F
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Fair value assumption	0.3356	0.3356
Remaining Term (in years) \| Series E
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Remaining term (in years)	4 years 6 months	5 years
Remaining Term (in years) \| Series F \| Minimum
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Remaining term (in years)	2 years 7 months 6 days	3 years 1 month 6 days
Remaining Term (in years) \| Series F \| Maximum
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Remaining term (in years)	6 years 6 months	7 years
Risk-free Interest Rate \| Series E
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Fair value assumption	2.7	2.2
Risk-free Interest Rate \| Series F \| Minimum
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Fair value assumption	2.6	2.0
Risk-free Interest Rate \| Series F \| Maximum
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Fair value assumption	2.8	2.3
Expected Volatility \| Series E
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Fair value assumption	43	43
Expected Volatility \| Series F
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Fair value assumption	43
Expected Volatility \| Series F \| Minimum
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Fair value assumption		43
Expected Volatility \| Series F \| Maximum
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Fair value assumption		44
Dividend Yield \| Series E
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Fair value assumption	0	0
Dividend Yield \| Series F
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Fair value assumption	0	0

Fair Value Measurement and Financial Instruments - Summary of Changes in Instruments Measured on Recurring Basis (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2018 USD ($)
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Balance at December 31, 2017	$ 478
Change in fair value	1,415
Balance at June 30, 2018	$ 1,893

Accounts Receivable - Composition of Accounts Receivable, Net (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Receivables [Abstract]
Gross accounts receivable - trade	$ 5,149	$ 4,684
Less: Allowances for doubtful accounts	(425)	(417)
Accounts receivable, net	$ 4,724	$ 4,267

Property and Equipment - Summary of Composition of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 3,421	$ 3,190
Less: Accumulated depreciation	(1,928)	(1,831)
Property and equipment, net	1,493	1,359
Laboratory Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	150	150
Office Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	493	487
Computer Equipment and Software
Property Plant And Equipment [Line Items]
Property and equipment, gross	874	680
Manufacturing Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	273	273
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property and equipment, gross	172	153
Rental Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 1,459	$ 1,447

Property and Equipment - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Property Plant And Equipment [Abstract]
Depreciation expense	$ 0.3	$ 0.1	$ 0.5	$ 0.3

Accrued Expenses - Summary of Composition of Accrued Expenses (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Payables And Accruals [Abstract]
Compensation and related benefits	$ 2,642	$ 4,465
Consulting and professional fees	2,701	461
Research and development expenses	303	497
Sales and marketing expenses	156	620
Warranty	653	570
Sales tax payable	331	322
Interest payable	235	188
Other	710	388
Accrued expenses	$ 7,731	$ 7,511

Debt - Summary of Composition of Debt (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Debt Disclosure [Abstract]
Outstanding principal	$ 30,000	$ 30,000
Accrued final payment fees	1,286	940
Less debt discounts	(1,289)	(1,384)
Total long-term debt, net	29,997	29,556
Less current portion of long-term debt	(2,500)
Long-term debt, net	$ 27,497	$ 29,556

Debt - Additional Information (Details) - USD ($) $ / shares in Units, shares in Thousands			1 Months Ended	3 Months Ended		6 Months Ended
	Jul. 02, 2018	Feb. 28, 2017	Mar. 31, 2017	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Debt Instrument [Line Items]
Interest expense				$ 900,000	$ 711,000	$ 1,821,000	$ 1,261,000
Cash interest expense				700,000	500,000	1,400,000	1,000,000
Non-cash interest expense				200,000	$ 200,000	$ 400,000	$ 300,000
Debt instrument, final payment fee			$ 1,000,000
Initial Public Offering \| Subsequent Event
Debt Instrument [Line Items]
Net proceeds from initial public offering	$ 100,000,000
$35.0 Million Credit Facility
Debt Instrument [Line Items]
Percentage of forecasted revenue to be achieved						75.00%
$35.0 Million Credit Facility \| Prepaid on or Before First Anniversary of Funding
Debt Instrument [Line Items]
Prepayment fees percentage						3.00%
$35.0 Million Credit Facility \| Prepaid After First and on or Before Second Anniversary of Funding
Debt Instrument [Line Items]
Prepayment fees percentage						2.00%
$35.0 Million Credit Facility \| Prepaid After Second Anniversary of Funding
Debt Instrument [Line Items]
Prepayment fees percentage						1.00%
$35.0 Million Credit Facility \| Oxford Finance LLC
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity		$ 25,000,000	35,000,000
Borrowings outstanding under credit facility				30,000,000		$ 30,000,000
Available borrowing achievement of trailing twelve month revenues				$ 45,000,000		$ 45,000,000
Debt instrument, interest rate				8.15%		8.15%
Warrants term				7 years		7 years
Percentage of borrowing capacity of tranche						3.95%
Borrowing capacity of tranche				$ 5,000,000		$ 5,000,000
Credit facility maturity date						Mar. 01, 2022
$35.0 Million Credit Facility \| Oxford Finance LLC \| LIBOR
Debt Instrument [Line Items]
Debt instrument, description of variable rate basis						30 day U.S. LIBOR
Basis spread on variable rate						7.38%
$35.0 Million Credit Facility \| Term A Loan
Debt Instrument [Line Items]
Interest-only period						2019-03
Amortization period without interest-only period extension						36 months
Extension of interest-only period upon achievement of revenues						12 months
Interest-only period upon achievement of revenues						2020-03
Amortization period upon extension of interest-only period						24 months
Final payment fees percentage						8.00%
Increase in final payment fees percentage upon extension interest only periods						8.50%
Effective interest rates				10.70%		10.70%		10.70%
$35.0 Million Credit Facility \| Term A Loan \| Series F Convertible Preferred Stock
Debt Instrument [Line Items]
Warrants issued to lender to purchase shares				588,498		588,498
Warrants issued at exercise price				$ 0.3356		$ 0.3356
Warrants expiration period						2024-03
$35.0 Million Credit Facility \| Term A Loan \| Oxford Finance LLC
Debt Instrument [Line Items]
Borrowings outstanding under credit facility			$ 25,000,000
$35.0 Million Credit Facility \| Term B Loan
Debt Instrument [Line Items]
Interest-only period						2019-03
Amortization period without interest-only period extension						36 months
Extension of interest-only period upon achievement of revenues						12 months
Interest-only period upon achievement of revenues						2020-03
Amortization period upon extension of interest-only period						24 months
Final payment fees percentage						7.00%
Increase in final payment fees percentage upon extension interest only periods						7.50%
Effective interest rates				11.60%		11.60%		11.60%
$35.0 Million Credit Facility \| Term B Loan \| Series F Convertible Preferred Stock
Debt Instrument [Line Items]
Warrants issued to lender to purchase shares				588,498		588,498
Warrants issued at exercise price				$ 0.3356		$ 0.3356
Warrants expiration period						2024-12
$35.0 Million Credit Facility \| Term B Loan \| Oxford Finance LLC
Debt Instrument [Line Items]
Borrowings outstanding under credit facility								$ 5,000,000
$35.0 Million Credit Facility \| Term C Loan \| Oxford Finance LLC
Debt Instrument [Line Items]
Line of credit facility, current borrowing capacity				$ 5,000,000		$ 5,000,000
Notification period for lenders to borrow loan upon achieving required revenue milestone						60 days
$25.0 Million Credit Facility \| Oxford Finance LLC
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity		$ 25,000,000
$25.0 Million Credit Facility \| Term A Loan
Debt Instrument [Line Items]
Final payment fees percentage		8.50%
$25.0 Million Credit Facility \| Term A Loan \| Minimum
Debt Instrument [Line Items]
Debt instrument, accrued interest rate		8.50%
$25.0 Million Credit Facility \| Term A Loan \| Maximum
Debt Instrument [Line Items]
Debt instrument, accrued interest rate		8.90%
$25.0 Million Credit Facility \| Term A Loan \| Oxford Finance LLC
Debt Instrument [Line Items]
Borrowings outstanding under credit facility		$ 15,000,000
$25.0 Million Credit Facility \| Term B Loan
Debt Instrument [Line Items]
Final payment fees percentage		4.70%
$25.0 Million Credit Facility \| Term B Loan \| Minimum
Debt Instrument [Line Items]
Debt instrument, accrued interest rate		8.50%
$25.0 Million Credit Facility \| Term B Loan \| Maximum
Debt Instrument [Line Items]
Debt instrument, accrued interest rate		8.90%
$25.0 Million Credit Facility \| Term B Loan \| Oxford Finance LLC
Debt Instrument [Line Items]
Borrowings outstanding under credit facility		$ 5,000,000
$25.0 Million Credit Facility \| Term C Loan \| Oxford Finance LLC
Debt Instrument [Line Items]
Line of credit facility, current borrowing capacity		$ 5,000,000

Debt - Schedule of Future Principal Payments (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Total principal payments	$ 30,000	$ 30,000
Term A and Term B Loans
Debt Instrument [Line Items]
2019	7,500
2020	10,000
2021	10,000
2022	2,500
Total principal payments	$ 30,000

Convertible Preferred Stock and Stockholders' Deficit - Additional Information (Details) - USD ($)		6 Months Ended
	Jul. 02, 2018	Jun. 30, 2018	Dec. 31, 2017	Mar. 31, 2017	Feb. 28, 2017
Stockholders Deficit [Line Items]
Common stock, par value per share		$ 0.01	$ 0.01
Common stock, shares authorized for issuance		413,918,000	413,918,000
Preferred stock, shares authorized for issuance		0	0
Preferred stock, par value per share		$ 0.01	$ 0.01
Common stock, shares issued		257,000	231,000
Common stock, shares outstanding		257,000	231,000
Convertible preferred stock, par value		$ 0.01	$ 0.01
Convertible preferred stock, shares authorized		308,593,000	308,593,000
Liquidation preference value		$ 108,324,000	$ 108,324,000
Convertible preferred stock non-cumulative dividends rate		9.00%
Common stock voting rights		one
Convertible Preferred Stock
Stockholders Deficit [Line Items]
Convertible preferred stock, par value		$ 0.01
Convertible preferred stock, shares authorized		308,600,000
Oxford Finance LLC
Stockholders Deficit [Line Items]
Convertible preferred stock converted to common stock, ratio		3.45%
Series D Convertible Preferred Stock
Stockholders Deficit [Line Items]
Convertible preferred stock, shares authorized		49,426,000	49,426,000
Convertible preferred stock converted to common stock, ratio		3.45%
Liquidation preference value		$ 14,205,000	$ 14,205,000
Series E Convertible Preferred Stock
Stockholders Deficit [Line Items]
Convertible preferred stock, shares authorized		44,873,000	44,873,000
Convertible preferred stock converted to common stock, ratio		3.45%
Liquidation preference value		$ 22,876,000	$ 22,876,000
Series F Convertible Preferred Stock
Stockholders Deficit [Line Items]
Convertible preferred stock, shares authorized		105,567,000	105,567,000
Convertible preferred stock converted to common stock, ratio		3.45%
Liquidation preference value		$ 34,343,000	$ 34,343,000
Additional liquidation preference		$ 0.1678
Additional liquidation preference per share due		$ 1.0068
Series G Convertible Preferred Stock
Stockholders Deficit [Line Items]
Convertible preferred stock, shares authorized		40,584,000	40,584,000
Convertible preferred stock converted to common stock, ratio		3.45%
Liquidation preference value		$ 15,000,000	$ 15,000,000
Series A-2 Convertible Preferred Stock
Stockholders Deficit [Line Items]
Convertible preferred stock, shares authorized		25,385,000	25,385,000
Convertible preferred stock converted to common stock, ratio		3.539%
Liquidation preference value		$ 5,209,000	$ 5,209,000
Series B Convertible Preferred Stock
Stockholders Deficit [Line Items]
Convertible preferred stock, shares authorized		17,000,000	17,000,000
Convertible preferred stock converted to common stock, ratio		4.103%
Liquidation preference value		$ 5,386,000	$ 5,386,000
Series C Convertible Preferred Stock
Stockholders Deficit [Line Items]
Convertible preferred stock, shares authorized		20,958,000	20,958,000
Convertible preferred stock converted to common stock, ratio		5.071%
Liquidation preference value		$ 11,009,000	$ 11,009,000
Junior Securities
Stockholders Deficit [Line Items]
Liquidation preference value		$ 59,200,000
$35.0 Million Credit Facility \| Oxford Finance LLC
Stockholders Deficit [Line Items]
Line of credit facility, maximum borrowing capacity				$ 35,000,000	$ 25,000,000
Subsequent Event
Stockholders Deficit [Line Items]
IPO closing date	Jul. 02, 2018
Subsequent Event \| Common Stock Warrants
Stockholders Deficit [Line Items]
Warrants issued to lender to purchase shares	100,000
Initial Public Offering \| Subsequent Event
Stockholders Deficit [Line Items]
Net proceeds from initial public offering	$ 100,000,000
Underwriting discounts and commissions before deducting offering expense	$ 7,500,000
Common stock, par value per share	$ 0.01
Common stock, shares authorized for issuance	200,000,000
Preferred stock, shares authorized for issuance	10,000,000
Preferred stock, par value per share	$ 0.01
Initial Public Offering \| Subsequent Event \| Common Stock
Stockholders Deficit [Line Items]
Common stock shares issued and sold	6,325,000
Exercise of underwriter's option to purchase additional shares	825,000
Issuance price per share	$ 17.00
Convertible preferred stock converted into common stock	11,000,000

Convertible Preferred Stock and Stockholders' Deficit - Summary of Common Stock Issued and Reserved for Issuance (Details) - shares	Jun. 30, 2018	Dec. 31, 2017
Stockholders Deficit [Line Items]
Shares of common stock issued	257,000	231,000
Shares of common stock reserved for issuance for:
Total shares of common stock issued and reserved for issuance	14,279,000
Series A-1 Convertible Preferred Stock
Shares of common stock reserved for issuance for:
Shares of common stock reserved for issuance	166,000
Series A-2 Convertible Preferred Stock
Shares of common stock reserved for issuance for:
Shares of common stock reserved for issuance	898,000
Series B Convertible Preferred Stock
Shares of common stock reserved for issuance for:
Shares of common stock reserved for issuance	697,000
Series C Convertible Preferred Stock
Shares of common stock reserved for issuance for:
Shares of common stock reserved for issuance	1,063,000
Series D Convertible Preferred Stock
Shares of common stock reserved for issuance for:
Shares of common stock reserved for issuance	1,705,000
Series E Convertible Preferred Stock
Shares of common stock reserved for issuance for:
Shares of common stock reserved for issuance	1,534,000
Series F Convertible Preferred Stock
Shares of common stock reserved for issuance for:
Shares of common stock reserved for issuance	3,531,000
Series G Convertible Preferred Stock
Shares of common stock reserved for issuance for:
Shares of common stock reserved for issuance	1,400,000
Series E Convertible Preferred Stock Warrants
Shares of common stock reserved for issuance for:
Shares of common stock reserved for issuance	14,000
Series F Convertible Preferred Stock Warrants
Shares of common stock reserved for issuance for:
Shares of common stock reserved for issuance	91,000
Warrants Issuable Upon Term C Loan Borrowing
Shares of common stock reserved for issuance for:
Shares of common stock reserved for issuance	20,000
Stock Options Outstanding
Shares of common stock reserved for issuance for:
Shares of common stock reserved for issuance	2,855,000
Shares Available for Grant Under Stock Incentive Plan
Shares of common stock reserved for issuance for:
Shares of common stock reserved for issuance	48,000

Convertible Preferred Stock and Stockholders' Deficit - Summary of Common Stock Issued and Reserved for Issuance (Parenthetical) (Details)	6 Months Ended
	Jun. 30, 2018
Series A-2 Convertible Preferred Stock
Stockholders Deficit [Line Items]
Convertible preferred stock converted to common stock, ratio	3.539%
Series B Convertible Preferred Stock
Stockholders Deficit [Line Items]
Convertible preferred stock converted to common stock, ratio	4.103%
Series C Convertible Preferred Stock
Stockholders Deficit [Line Items]
Convertible preferred stock converted to common stock, ratio	5.071%

Convertible Preferred Stock and Stockholders' Deficit - Summary of Outstanding Convertible Preferred Stock (Details) - USD ($) $ / shares in Units, $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Class Of Stock [Line Items]
Shares Authorized and Designated	308,593,000	308,593,000
Shares Issued and Outstanding	304,958,000	304,958,000
Carrying Value	$ 187,136	$ 187,136
Liquidation Value	$ 108,324	$ 108,324
Series A-1 Convertible Preferred Stock
Class Of Stock [Line Items]
Shares Authorized and Designated	4,800,000	4,800,000
Shares Issued and Outstanding	4,800,000	4,800,000
Carrying Value	$ 900	$ 900
Liquidation Value per Share	$ 0.0617	$ 0.0617
Liquidation Value	$ 296	$ 296
Series A-2 Convertible Preferred Stock
Class Of Stock [Line Items]
Shares Authorized and Designated	25,385,000	25,385,000
Shares Issued and Outstanding	25,385,000	25,385,000
Carrying Value	$ 16,428	$ 16,428
Liquidation Value per Share	$ 0.2052	$ 0.2052
Liquidation Value	$ 5,209	$ 5,209
Series B Convertible Preferred Stock
Class Of Stock [Line Items]
Shares Authorized and Designated	17,000,000	17,000,000
Shares Issued and Outstanding	17,000,000	17,000,000
Carrying Value	$ 16,859	$ 16,859
Liquidation Value per Share	$ 0.3168	$ 0.3168
Liquidation Value	$ 5,386	$ 5,386
Series C Convertible Preferred Stock
Class Of Stock [Line Items]
Shares Authorized and Designated	20,958,000	20,958,000
Shares Issued and Outstanding	20,958,000	20,958,000
Carrying Value	$ 34,841	$ 34,841
Liquidation Value per Share	$ 0.5253	$ 0.5253
Liquidation Value	$ 11,009	$ 11,009
Series D Convertible Preferred Stock
Class Of Stock [Line Items]
Shares Authorized and Designated	49,426,000	49,426,000
Shares Issued and Outstanding	49,426,000	49,426,000
Carrying Value	$ 29,970	$ 29,970
Liquidation Value per Share	$ 0.2874	$ 0.2874
Liquidation Value	$ 14,205	$ 14,205
Series E Convertible Preferred Stock
Class Of Stock [Line Items]
Shares Authorized and Designated	44,873,000	44,873,000
Shares Issued and Outstanding	44,471,000	44,471,000
Carrying Value	$ 29,800	$ 29,800
Liquidation Value per Share	$ 0.5144	$ 0.5144
Liquidation Value	$ 22,876	$ 22,876
Series F Convertible Preferred Stock
Class Of Stock [Line Items]
Shares Authorized and Designated	105,567,000	105,567,000
Shares Issued and Outstanding	102,334,000	102,334,000
Carrying Value	$ 43,513	$ 43,513
Liquidation Value per Share	$ 0.3356	$ 0.3356
Liquidation Value	$ 34,343	$ 34,343
Series G Convertible Preferred Stock
Class Of Stock [Line Items]
Shares Authorized and Designated	40,584,000	40,584,000
Shares Issued and Outstanding	40,584,000	40,584,000
Carrying Value	$ 14,825	$ 14,825
Liquidation Value per Share	$ 0.3696	$ 0.3696
Liquidation Value	$ 15,000	$ 15,000

Convertible Preferred Stock and Stockholders' Deficit - Summary of Outstanding Convertible Preferred Stock Warrants (Details) shares in Thousands	6 Months Ended
	Jun. 30, 2018 $ / shares shares
Class Of Warrant Or Right [Line Items]
Warrants Outstanding	3,046
Series E Convertible Preferred Stock Warrants
Class Of Warrant Or Right [Line Items]
Warrants Outstanding	402
Exercise Price \| $ / shares	$ 0.6746
Expiration Date	2022-12
Series F Convertible Preferred Stock Warrants
Class Of Warrant Or Right [Line Items]
Warrants Outstanding	878
Exercise Price \| $ / shares	$ 0.3356
Expiration Date	2021-02
Series F Convertible Preferred Stock Warrants
Class Of Warrant Or Right [Line Items]
Warrants Outstanding	589
Exercise Price \| $ / shares	$ 0.3356
Expiration Date	2023-08
Series F Convertible Preferred Stock Warrants
Class Of Warrant Or Right [Line Items]
Warrants Outstanding	589
Exercise Price \| $ / shares	$ 0.3356
Expiration Date	2024-03
Series F Convertible Preferred Stock Warrants
Class Of Warrant Or Right [Line Items]
Warrants Outstanding	588
Exercise Price \| $ / shares	$ 0.3356
Expiration Date	2024-12

Loss Per Share - Schedule of Potentially Dilutive Securities Outstanding Excluded from Diluted Loss Per Share Calculation (Details) - shares shares in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Stock Options Outstanding
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities outstanding excluded from diluted loss per share	2,855	2,076
Non-vested Restricted Stock Awards
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities outstanding excluded from diluted loss per share	10	17
Convertible Preferred Stock Warrants
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities outstanding excluded from diluted loss per share	105	85
Shares of Convertible Preferred Stock “as-converted”
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities outstanding excluded from diluted loss per share	10,994	10,994

Share-Based Compensation - Summary of Share-Based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total	$ 192	$ 156	$ 336	$ 198
Cost of Revenues
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total	5	7	9	7
Selling and Marketing
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total	65	43	119	56
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total	87	92	142	108
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total	$ 35	$ 14	$ 66	$ 27

Share-Based Compensation - Additional Information (Details) $ / shares in Units, $ in Thousands	1 Months Ended	3 Months Ended		6 Months Ended
	Apr. 30, 2018 USD ($) Installment $ / shares shares	Jun. 30, 2018 USD ($) shares	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($) $ / shares shares	Jun. 30, 2017 USD ($)
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation expenses		$ 192	$ 156	$ 336	$ 198
Unrecognized compensation cost related to non-vested stock options		2,700		$ 2,700
Weighted-average grant-date fair value of stock options granted \| $ / shares				$ 3.64
Intrinsic value of stock options exercised				$ 100
Options to purchase shares \| shares	54,794
Option exercise price \| $ / shares	$ 5.22
Stock option vesting period monthly installment \| Installment	12
Estimated grant-date fair value of option awards	$ 200
Stock Options Outstanding
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation expenses		$ 200	$ 200	$ 300	$ 200
Non-vested awards not yet recognized weighted-average period for recognition				3 years 2 months 12 days
Restricted Stock Awards [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Non-vested awards not yet recognized weighted-average period for recognition				9 months
Fair value of restricted stock awards vested				$ 50
2003 Stock Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting terms of stock options				Stock options vest 25% upon the first anniversary of the date of grant and the remainder ratably monthly thereafter for 36 months
Shares available for future issuance \| shares		50,000		50,000
2003 Stock Incentive Plan \| First Anniversary of Date of Grant
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting percentage of stock options				25.00%
2003 Stock Incentive Plan \| Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares authorized for issuance \| shares		3,100,000		3,100,000
Maximum contractual term of stock options				10 years

Share-Based Compensation - Summary of Stock Option Activity (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted-average Exercise Price per Option, Granted	$ 5.94
Stock Options Outstanding
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Shares under Option, Outstanding, Beginning balance	2,444
Number of Shares under Option, Granted	502
Number of Shares under Option, Exercised	(26)
Number of Shares under Option, Forfeited	(65)
Number of Shares under Option, Outstanding, Ending balance	2,855	2,444
Number of Shares under Option, Exercisable	1,426
Number of Shares under Option, Vested and expected to vest	2,855
Weighted-average Exercise Price per Option, Outstanding, Beginning balance	$ 2.39
Weighted-average Exercise Price per Option, Granted	5.94
Weighted-average Exercise Price per Option, Exercised	1.43
Weighted-average Exercise Price per Option, Forfeited	3.20
Weighted-average Exercise Price per Option, Outstanding, Ending balance	3.00	$ 2.39
Weighted-average Exercise Price per Option, Exercisable	2.22
Weighted-average Exercise Price per Option, Vested and expected to vest	$ 3.00
Weighted-average Remaining Contractual Life, Outstanding	7 years 7 months 6 days	7 years 8 months 12 days
Weighted-average Remaining Contractual Life, Exercisable	6 years 3 months 18 days
Weighted-average Remaining Contractual Life, Vested and expected to vest	7 years 7 months 6 days
Aggregate Intrinsic Value, Outstanding	$ 67,395
Aggregate Intrinsic Value, Exercisable	34,779
Aggregate Intrinsic Value, Vested and expected to vest	$ 67,395

Share-Based Compensation - Summary of Weighted-average Inputs and Assumptions used to Estimate Grant-date Fair Value of Stock Options (Details)	6 Months Ended
	Jun. 30, 2018 $ / shares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Estimated fair value of common stock	$ 5.94
Weighted-average Exercise Price per Option, Granted	$ 5.94
Expected term (in years)	6 years
Risk-free interest rate	2.70%
Expected volatility	65.80%
Dividend yield	0.00%

Share-Based Compensation - Summary of Restricted Stock Award Activity (Details) - Restricted Stock Awards [Member] shares in Thousands	6 Months Ended
	Jun. 30, 2018 $ / shares shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Non-vested Restricted Stock Awards, Beginning balance \| shares	16
Non-vested Restricted Stock Awards, Vested \| shares	(6)
Non-vested Restricted Stock Awards, Ending balance \| shares	10
Weighted-average Grant-date Fair Value, Non-vested, Beginning balance \| $ / shares	$ 2.32
Weighted-average Grant-date Fair Value, Vested \| $ / shares	2.32
Weighted-average Grant-date Fair Value, Non-vested, Ending balance \| $ / shares	$ 2.32

Employee Benefit Plans - Additional Information (Details)	6 Months Ended
	Jun. 30, 2018
Defined Benefit Plan Disclosure [Line Items]
Defined contribution retirement plan, plan name	401(k) plan
401(k) Plan
Defined Benefit Plan Disclosure [Line Items]
Defined contribution retirement plan, maximum employee contribution deferred	100.00%

Commitments and Contingencies - Additional Information (Details)	Jan. 31, 2013
Commitments And Contingencies Disclosure [Abstract]
Lease term	93 months

Geographical Segment Information - Additional Information (Details)	6 Months Ended
	Jun. 30, 2018 Segment
Segments Geographical Areas [Abstract]
Number of operating business segment	1

Geographical Segment Information - Summary of Revenue Generated in Geographic Regions for Years Indicated (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Segment Reporting Information [Line Items]
Revenues	$ 13,252	$ 10,308	$ 23,404	$ 17,834
Revenues \| Geographic Concentration
Segment Reporting Information [Line Items]
Revenues	$ 13,252	$ 10,308	$ 23,404	$ 17,834
Percentage of Revenues	100.00%	100.00%	100.00%	100.00%
Revenues \| United States \| Geographic Concentration
Segment Reporting Information [Line Items]
Revenues	$ 12,898	$ 10,225	$ 22,870	$ 17,619
Percentage of Revenues	97.00%	99.00%	98.00%	99.00%
Revenues \| International \| Geographic Concentration
Segment Reporting Information [Line Items]
Revenues	$ 354	$ 83	$ 534	$ 215
Percentage of Revenues	3.00%	1.00%	2.00%	1.00%