Neuronetics (STIM) 10-Q 6 Nov 18 2018 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2018	Oct. 31, 2018
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q3
Trading Symbol	STIM
Entity Registrant Name	NEURONETICS, INC.
Entity Central Index Key	1,227,636
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Common Stock, Shares Outstanding		17,579,491

Balance Sheets

Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 106,760	$ 29,147
Accounts receivable, net	5,283	4,267
Inventory	2,614	2,468
Prepaid expenses and other current assets	2,082	1,123
Total current assets	116,739	37,005
Property and equipment, net	1,343	1,359
Other assets	897	574
Total Assets	118,979	38,938
Current liabilities:
Accounts payable	2,102	2,513
Accrued expenses	6,383	7,511
Deferred revenue	1,813	1,970
Current portion of long-term debt	5,000	0
Total current liabilities	15,298	11,994
Long-term debt, net	25,198	29,556
Deferred revenue	2,032	2,275
Deferred rent	103	151
Convertible preferred stock warrant liability		478
Total Liabilities	42,631	44,454
Commitments and contingencies (Note 14)
Convertible preferred stock, $0.01 par value: 308,593 shares previously authorized prior to initial public offering, issuable in series; no and 304,958 shares issued and outstanding at September 30, 2018 and December 31, 2017, respectively; no liquidation value at September 30, 2018		187,136
Stockholders’ Equity (Deficit):
Preferred stock, $0.01 par value: 10,000 shares authorized; no shares issued or outstanding at September 30, 2018 and December 31, 2017
Common stock, $0.01 par value: 200,000 shares authorized; 17,579 and 231 shares issued and outstanding at September 30, 2018 and December 31, 2017, respectively	176	2
Additional paid-in capital	291,072	4,292
Accumulated deficit	(214,900)	(196,946)
Total Stockholders' Equity (Deficit)	76,348	(192,652)
Total Liabilities, Convertible Preferred Stock and Stockholders’ Equity (Deficit)	$ 118,979	$ 38,938

Balance Sheets (Parenthetical)

Balance Sheets (Parenthetical) - USD ($)	Sep. 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	0	304,958,000
Convertible preferred stock, outstanding	0	304,958,000
Liquidation preference	$ 0
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	17,579,000	231,000
Common stock, shares outstanding	17,579,000	231,000

Statements of Operations

Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Statement [Abstract]
Revenues	$ 13,737	$ 10,491	$ 37,141	$ 28,325
Cost of revenues	3,034	2,636	8,736	6,675
Gross Profit	10,703	7,855	28,405	21,650
Operating expenses:
Sales and marketing	9,672	6,566	27,616	19,272
General and administrative	3,238	2,256	8,952	5,735
Research and development	2,125	1,843	6,010	6,018
Total operating expenses	15,035	10,665	42,578	31,025
Loss from Operations	(4,332)	(2,810)	(14,173)	(9,375)
Other (income) expense:
Interest expense	928	807	2,749	2,068
Other expense (income), net	(299)	136	1,032	(308)
Net Loss	$ (4,961)	$ (3,753)	$ (17,954)	$ (11,135)
Net loss per share of common stock outstanding, basic and diluted	$ (0.29)	$ (19.35)	$ (2.99)	$ (62.56)
Weighted-average common shares outstanding, basic and diluted	17,382	194	6,014	178

Statement of Changes in Convert

Statement of Changes in Convertible Preferred Stock and Stockholders' Equity (Deficit) - 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 at Dec. 31, 2017	$ 187,136	$ 187,136
Beginning balance, shares at Dec. 31, 2017	304,958,000	304,958,000
Exercises of stock options	$ 31		$ 1	30
Exercises of stock options, shares			20,000
Share-based compensation expense	144			144
Net loss	(5,497)				(5,497)
Ending balance at Mar. 31, 2018	(197,974)		$ 3	4,466	(202,443)
Ending balance, shares at Mar. 31, 2018			251,000
Ending balance at Mar. 31, 2018		$ 187,136
Ending balance, shares at Mar. 31, 2018		304,958,000
Beginning balance at Dec. 31, 2017	(192,652)		$ 2	4,292	(196,946)
Beginning balance, shares at Dec. 31, 2017			231,000
Beginning balance at Dec. 31, 2017	$ 187,136	$ 187,136
Beginning balance, shares at Dec. 31, 2017	304,958,000	304,958,000
Net loss	$ (17,954)
Ending balance at Sep. 30, 2018	$ 76,348		$ 176	291,072	(214,900)
Ending balance, shares at Sep. 30, 2018			17,579,000
Ending balance, shares at Sep. 30, 2018	0
Beginning balance at Mar. 31, 2018	$ (197,974)		$ 3	4,466	(202,443)
Beginning balance, shares at Mar. 31, 2018			251,000
Beginning balance at Mar. 31, 2018		$ 187,136
Beginning balance, shares at Mar. 31, 2018		304,958,000
Exercises of stock options	7			7
Exercises of stock options, shares			6,000
Share-based compensation expense	192			192
Net loss	(7,496)				(7,496)
Ending balance at Jun. 30, 2018	(205,271)		$ 3	4,665	(209,939)
Ending balance, shares at Jun. 30, 2018			257,000
Ending balance at Jun. 30, 2018		$ 187,136
Ending balance, shares at Jun. 30, 2018		304,958,000
Conversion of convertible preferred stock into common stock	187,136	$ (187,136)	$ 109	187,027
Conversion of convertible preferred stock into common stock, shares		(304,958,000)	10,994,000
Conversion of convertible preferred stock warrants into common stock warrants	1,874			1,874
Issuance of common stock in initial public offering, net of issuance costs of $3.464	96,535		$ 64	96,471
Issuance of common stock in initial public offering, net of issuance costs of $3.464, shares			6,325,000
Exercises of stock options	7			7
Exercises of stock options, shares			3,000
Share-based compensation expense	1,028			1,028
Net loss	(4,961)				(4,961)
Ending balance at Sep. 30, 2018	$ 76,348		$ 176	$ 291,072	$ (214,900)
Ending balance, shares at Sep. 30, 2018			17,579,000
Ending balance, shares at Sep. 30, 2018	0

Statement of Changes in Conve_2

Statement of Changes in Convertible Preferred Stock and Stockholders' Equity (Deficit) (Parenthetical) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2018
Statement Of Stockholders Equity [Abstract]
Issuance of common stock in initial public offering, issuance costs	$ 3,465	$ 3,465

Statements of Cash Flows (Unaud

Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Cash Flows from Operating Activities:
Net loss		$ (17,954)	$ (11,135)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization		671	455
Share-based compensation		1,364	295
Non-cash interest expense		642	542
Change in fair value of convertible preferred stock warrant liability		1,396	(250)
Cost of rental units purchased by customers		148	118
Changes in certain assets and liabilities:
Accounts receivable, net		(1,016)	(326)
Inventory		(767)	(519)
Prepaid expenses and other assets		(298)	(30)
Accounts payable		(594)	(819)
Accrued expenses		(1,461)	331
Deferred revenue		(400)	(45)
Deferred rent		(46)	(29)
Net Cash Used in Operating Activities		(18,315)	(11,412)	$ (11,100)
Cash Flows from Investing Activities:
Purchases of property and equipment and capitalized software		(650)	(319)
Net Cash Used in Investing Activities		(650)	(319)
Cash Flows from Financing Activities:
Proceeds from issuance of common stock in initial public offering		99,998
Payments of public offering costs	$ (3,465)	(3,465)
Proceeds from exercises of stock options		45	30
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 Provided by Financing Activities		96,578	18,840
Net Increase in Cash and Cash Equivalents		77,613	7,109
Cash and Cash Equivalents, Beginning of Period		29,147	17,040	17,040
Cash and Cash Equivalents, End of Period	$ 106,760	106,760	24,149	$ 29,147
Supplemental disclosure of cash flow information:
Cash paid for interest		2,057	1,492
Transfer of inventory to property and equipment		235	248
Supplemental disclosure of non-cash financing activities:
Allocation of proceeds from debt financing to convertible preferred stock warrant liability			$ 171
Conversion of convertible preferred stock into common stock		187,136
Conversion of convertible preferred stock warrants into common stock warrants		$ 1,874

Description of Business

Description of Business	9 Months Ended
	Sep. 30, 2018
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Description of Business	1. 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 shares sold pursuant to an option granted to the underwriters to purchase additional shares at a public offering price of $17.00 per share. The Company received net proceeds of $96.5 million after deducting underwriting discounts, commissions and other offering expenses paid by the Company. The Company’s common stock is listed on the Nasdaq Global Market under the trading symbol “STIM.” In addition, immediately prior to the closing of the IPO on July 2, 2018, (i) all of the Company’s outstanding shares of convertible preferred stock converted into an aggregate 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 September 30, 2018, the Company had cash and cash equivalents of $106.8 million and an accumulated deficit of $214.9 million. The Company incurred negative cash flows from operating activities of $11.1 million for the year ended December 31, 2017 and $18.3 million for the nine months ended September 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 proceeds from its IPO, private placements of its convertible preferred securities, borrowings under its credit facilities and revenues from sales of its products. As of September 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 September 30, 2018 and anticipated revenues from sales of its products are sufficient to fund the Company’s operations for at least the next 24 months after September 30, 2018.

Basis of Presentation

Basis of Presentation	9 Months Ended
	Sep. 30, 2018
Accounting Policies [Abstract]
Basis of Presentation	2. The accompanying financial statements have been prepared in accordance with United States generally accepted accounting principles, 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 ASUs, 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 nine months ended September 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 paid 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 Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2018
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	3. 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 Pronouncement

Recent Accounting Pronouncements	9 Months Ended
	Sep. 30, 2018
New Accounting Pronouncements And Changes In Accounting Principles [Abstract]
Recent Accounting Pronouncements	4. 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) Revenue from Contracts with Customers (Topic 606): Deferral of the Effective Date Revenue from Contracts with Customers (Topic 606): Identifying Performance Obligations and Licensing Revenue from Contracts with Customers (Topic 606): Narrow-Scope Improvements and Practical Expedients 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 $1.3 million as of September 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

Fair Value Measurement and Fina

Fair Value Measurement and Financial Instruments	9 Months Ended
	Sep. 30, 2018
Fair Value Disclosures [Abstract]
Fair Value Measurement and Financial Instruments	5. 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 September 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 September 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 September 30, 2018 and December 31, 2017 (in thousands): September 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) $ 86,605 $ 86,605 $ 86,605 $ - $ - 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 July 2, 2018 and December 31, 2017: July 2, 2018 December 31, 2017 Series E Series F Series E Series F Estimated fair value of convertible preferred stock $ 26.41 $ 26.41 $ 9.57 $ 11.01 Exercise price $ 19.55 $ 9.73 $ 19.55 $ 9.73 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 nine months ended September 30, 2018 (in thousands): Balance at December 31, 2017 $ 478 Change in fair value 1,396 Reclassification to additional paid in capital (1,874 ) Balance at September 30, 2018 $ -

Accounts Receivable

Accounts Receivable	9 Months Ended
	Sep. 30, 2018
Receivables [Abstract]
Accounts Receivable	6. The following table presents the composition of accounts receivable, net as of September 30, 2018 and December 31, 2017 (in thousands): September 30, 2018 December 31, 2017 Gross accounts receivable - trade $ 5,742 $ 4,684 Less: Allowances for doubtful accounts (459 ) (417 ) Accounts receivable, net $ 5,283 $ 4,267

Property and Equipment and Capi

Property and Equipment and Capitalized Software	9 Months Ended
	Sep. 30, 2018
Property Plant And Equipment [Abstract]
Property and Equipment and Capitalized Software	7. The following table presents the composition of property and equipment, net as of September 30, 2018 and December 31, 2017 (in thousands): September 30, 2018 December 31, 2017 Laboratory equipment $ 150 $ 150 Office equipment 493 487 Computer equipment and software 937 680 Manufacturing equipment 273 273 Leasehold improvements 172 153 Rental equipment 1,293 1,447 Property and equipment, gross 3,318 3,190 Less: Accumulated depreciation (1,975 ) (1,831 ) Property and equipment, net $ 1,343 $ 1,359 As of September 30, 2018 and December 31, 2017, the Company had capitalized software costs, net of $0.7 million and $0.4 million, respectively, which are included in “Other assets” on the balance sheet. Depreciation and amortization expense was $0.2 million and $0.1 million for the three months ended September 30, 2018 and 2017, respectively, and $0.7 million and $0.5 million for the nine months ended September 30, 2018 and 2017, respectively.

Accrued Expenses

Accrued Expenses	9 Months Ended
	Sep. 30, 2018
Payables And Accruals [Abstract]
Accrued expenses	8. The following table presents the composition of accrued expenses as of September 30, 2018 and December 31, 2017 (in thousands): September 30, 2018 December 31, 2017 Compensation and related benefits $ 3,402 $ 4,465 Consulting and professional fees 833 461 Research and development expenses 209 497 Sales and marketing expenses 148 620 Warranty 650 570 Sales tax payable 376 322 Interest payable 237 188 Other 528 388 Accrued expenses $ 6,383 $ 7,511

Debt

Debt	9 Months Ended
	Sep. 30, 2018
Debt Disclosure [Abstract]
Debt	9. The following table presents the composition of debt as of September 30, 2018 and December 31, 2017 (in thousands): September 30, 2018 December 31, 2017 Outstanding principal $ 30,000 $ 30,000 Accrued final payment fees 1,377 940 Less debt discounts (1,179 ) (1,384 ) Total long-term debt, net 30,198 29,556 Less current portion of long-term debt (5,000 ) - Long-term debt, net $ 25,198 $ 29,556 For the three months ended September 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 September 30, 2017, the Company recognized interest expense of $0.8 million, of which $0.5 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. For the nine months ended September 30, 2018, the Company recognized interest expense of $2.7 million, of which $2.1 million was cash and $0.6 million was non-cash interest expense related to the amortization of deferred debt issuance costs and accrual of final payment fees. For the nine months ended September 30, 2017, the Company recognized interest expense of $2.1 million, of which $1.6 million was cash and $0.5 million was non-cash interest expense related to the amortization of deferred debt issuance costs and accrual of final payment fees. Current 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 allowed 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 Oxford if it elected to borrow the Term C Loan. As a result of completing its IPO on July 2, 2018 and receiving the net proceeds therefrom, the Company elected not to borrow the additional $5.0 million, and it is no longer available to the Company. 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 September 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 Oxford a warrant to purchase shares of its Series F convertible preferred stock. This convertible preferred stock warrant converted into a warrant to purchase 20,303 shares of the Company’s common stock at an exercise price of $9.73 per share. The warrant will expire in March 2024. 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 Oxford a warrant to purchase shares of its Series F convertible preferred stock. This convertible preferred stock warrant converted into a warrant to purchase 20,303 shares of the Company’s common stock at an exercise price of $9.73 per share. The warrant will expire in December 2024. In addition to principal and interest payments due under the credit facility, the Company is required to make final payment fees to Oxford 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 September 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 Oxford 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 Oxford 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 September 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 Oxford 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 Oxford 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 Oxford $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

Convertible Preferred Stock and Stockholders' Deficit	9 Months Ended
	Sep. 30, 2018
Equity [Abstract]
Convertible Preferred Stock and Stockholders' Deficit	10. 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 shares sold pursuant to an option granted to the underwriters to purchase additional shares, at a public offering price of $17.00 per share. The Company received net proceeds of $96.5 million after deducting underwriting discounts, commissions, and other offering expenses paid by the Company. In addition, immediately prior to the closing of the IPO on July 2, 2018, (i) all of the Company’s outstanding shares of convertible preferred stock converted into an aggregate of 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 and restated certificate of incorporation as of September 30, 2018 authorized the issuance of 200.0 million shares of common stock, $0.01 par value per share, of which 17.6 million were issued and outstanding as of September 30, 2018. Prior to the IPO, 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 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 September 30, 2018 and December 31, 2017 (in thousands): September 30, 2018 December 31, 2017 Shares of common stock issued 17,579 231 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 Common stock warrants outstanding 105 - Stock options outstanding 2,873 2,444 Restricted stock units outstanding 38 - Shares available for grant under stock incentive plan 1,323 246 Shares available for sale under employee stock purchase plan 244 - Total shares of common stock issued and reserved for issuance 22,162 14,040 ___________________________ (1) Shares of Series A-2 convertible preferred stock converted 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 converted 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 converted 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. Holders of common stock are entitled to receive 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. 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 an aggregate of 11.0 million shares of common stock, resulting in the elimination of the Company’s outstanding liquidation preferences. Common Stock Warrants The following table summarizes the Company’s outstanding common stock warrants as of September 30, 2018: Warrants Outstanding (in thousands) Exercise Price Expiration Date 14 $ 19.55 Dec-2022 30 $ 9.73 Feb-2021 20 $ 9.73 Aug-2023 20 $ 9.73 Mar-2024 21 $ 9.73 Dec-2024 105

Loss Per Share

Loss Per Share	9 Months Ended
	Sep. 30, 2018
Earnings Per Share [Abstract]
Loss Per Share	11. 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 and units 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 September 30, 2018 and 2017 have been excluded from the denominator of the diluted loss per share of common stock outstanding calculation (in thousands): September 30, 2018 2017 Stock options 2,873 2,305 Non-vested restricted stock awards 7 15 Non-vested restricted stock units 38 - Convertible preferred stock warrants - 85 Common stock warrants 105 - Shares of convertible preferred stock “as-converted” - 10,994

Share-based Compensation

Share-based Compensation	9 Months Ended
	Sep. 30, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Share-based Compensation	12. The amount of share-based compensation expense recognized by the Company by location in its statements of operations for the three and nine months ended September 30, 2018 and 2017 is as follows (in thousands): Three Months ended September 30, Nine Months ended September 30, 2018 2017 2018 2017 Cost of revenues $ 6 $ 5 $ 15 $ 12 Sales and marketing 709 38 828 94 General and administrative 273 40 415 148 Research and development 40 14 106 41 Total $ 1,028 $ 97 $ 1,364 $ 295 2018 Equity Incentive Plan In June 2018, the Company adopted the 2018 Equity Incentive Plan, or 2018 Plan, which authorized the issuance of up to 1.4 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 units to one member of senior management and to an independent member of its board of directors as compensation for board service. All stock options granted to date have had exercise prices equal to the fair value, as determined by the closing price as reported by the Nasdaq Global Market, of the underlying common stock on the date of 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 September 30, 2018, there were 1.3 million shares available for future issuance under the 2018 plan. 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 September 30, 2018, there were no 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. Stock Options The following table summarizes the Company’s stock option activity for the nine months ended September 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 535 $ 7.19 Exercised (29 ) $ 1.58 Forfeited (77 ) $ 3.13 Outstanding at September 30, 2018 2,873 $ 3.27 7.2 $ 82,739 Exercisable at September 30, 2018 1,642 $ 2.23 5.9 $ 48,967 Vested and expected to vest at September 30, 2018 2,873 $ 3.27 7.2 $ 82,739 The Company recognized share-based compensation expense related to stock options of $1.0 million and $0.1 million for the three months ended September 30, 2018 and 2017, respectively, and $1.3 million and $0.2 million for the nine months ended September 30, 2018 and 2017, respectively. As of September 30, 2018, there was $2.9 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 nine months ended September 30, 2018 was estimated at $4.38 per option. The total intrinsic value of stock options exercised during the nine months ended September 30, 2018 was $0.1 million. For the nine months ended September 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 $ 7.19 Exercise price $ 7.19 Expected term (in years) 6.0 Risk-free interest rate 2.7 % Expected volatility 65.6 % 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 recognized 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 and Restricted Stock Units The following table summarizes the Company’s restricted stock award and restricted stock unit activity for the nine months ended September 30, 2018: Non-vested Restricted Stock Awards (in thousands) Weighted- average Grant-date Fair Value Non-vested Restricted Stock Units (in thousands) Weighted- average Grant-date Fair Value Non-vested at December 31, 2017 16 $ 2.32 - $ - Granted - $ - 38 $ 25.92 Vested (9 ) $ 2.32 - $ - Non-vested at September 30, 2018 7 $ 2.32 38 $ 25.92 The Company recognized approximately $0.1 million in share-based compensation expense related to restricted stock awards and restricted stock units during the three and nine months ended September 30, 2018 and 2017. As of September 30, 2018, there was $0.9 million of unrecognized compensation cost related to non-vested restricted stock awards and restricted stock units, which the Company expects to recognize over a weighted-average period of 3.6 years. The total fair value at the vesting date of restricted stock awards and restricted stock units vested during the nine months ended September 30, 2018 was $0.2 million.

Employee Benefit Plans

Employee Benefit Plans	9 Months Ended
	Sep. 30, 2018
Compensation And Retirement Disclosure [Abstract]
Employee Benefit Plans	13. 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. 2018 Employee Stock Purchase Plan In July 2018, the Company adopted the 2018 Employee Stock Purchase Plan, or 2018 ESPP, with an initial 0.2 million share reserve, subject to automatic annual increases on January 1st of each year for a period of up to ten years, as defined in the plan document. The purpose of the 2018 ESPP is to enhance employee interest in the success and progress of the Company by encouraging employee ownership of common stock of the Company. The 2018 ESPP provides the opportunity to purchase the Company’s common stock at a 15% discount to the market price through payroll deductions or lump sum cash investments. As of September 30, 2018, the Company had not yet approved any offering under the 2018 ESPP.

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2018
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	14. 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 Informatio

Geographical Segment Information	9 Months Ended
	Sep. 30, 2018
Segments Geographical Areas [Abstract]
Geographical Segment Information	15. 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 September 30, 2018 2017 Amount % of Revenues Amount % of Revenues United States $ 13,518 98 % $ 10,398 99 % International 219 2 % 93 1 % Total revenues $ 13,737 100 % $ 10,491 100 % Revenues by Geography Nine Months ended September 30, 2018 2017 Amount % of Revenues Amount % of Revenues United States $ 36,388 98 % $ 28,017 99 % International 753 2 % 308 1 % Total revenues $ 37,141 100 % $ 28,325 100 %

Basis of Presentation (Policies

Basis of Presentation (Policies)	9 Months Ended
	Sep. 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 nine months ended September 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 paid 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 Fi_2

Fair Value Measurement and Financial Instruments (Tables)	9 Months Ended
	Sep. 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 September 30, 2018 and December 31, 2017 (in thousands): September 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) $ 86,605 $ 86,605 $ 86,605 $ - $ - 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	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 July 2, 2018 and December 31, 2017: July 2, 2018 December 31, 2017 Series E Series F Series E Series F Estimated fair value of convertible preferred stock $ 26.41 $ 26.41 $ 9.57 $ 11.01 Exercise price $ 19.55 $ 9.73 $ 19.55 $ 9.73 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 nine months ended September 30, 2018 (in thousands): Balance at December 31, 2017 $ 478 Change in fair value 1,396 Reclassification to additional paid in capital (1,874 ) Balance at September 30, 2018 $ -

Accounts Receivable (Tables)

Accounts Receivable (Tables)	9 Months Ended
	Sep. 30, 2018
Receivables [Abstract]
Composition of Accounts Receivable, Net	The following table presents the composition of accounts receivable, net as of September 30, 2018 and December 31, 2017 (in thousands): September 30, 2018 December 31, 2017 Gross accounts receivable - trade $ 5,742 $ 4,684 Less: Allowances for doubtful accounts (459 ) (417 ) Accounts receivable, net $ 5,283 $ 4,267

Property and Equipment and Ca_2

Property and Equipment and Capitalized Software (Tables)	9 Months Ended
	Sep. 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 September 30, 2018 and December 31, 2017 (in thousands): September 30, 2018 December 31, 2017 Laboratory equipment $ 150 $ 150 Office equipment 493 487 Computer equipment and software 937 680 Manufacturing equipment 273 273 Leasehold improvements 172 153 Rental equipment 1,293 1,447 Property and equipment, gross 3,318 3,190 Less: Accumulated depreciation (1,975 ) (1,831 ) Property and equipment, net $ 1,343 $ 1,359

Accrued Expenses (Tables)

Accrued Expenses (Tables)	9 Months Ended
	Sep. 30, 2018
Payables And Accruals [Abstract]
Summary of Composition of Accrued Expenses	The following table presents the composition of accrued expenses as of September 30, 2018 and December 31, 2017 (in thousands): September 30, 2018 December 31, 2017 Compensation and related benefits $ 3,402 $ 4,465 Consulting and professional fees 833 461 Research and development expenses 209 497 Sales and marketing expenses 148 620 Warranty 650 570 Sales tax payable 376 322 Interest payable 237 188 Other 528 388 Accrued expenses $ 6,383 $ 7,511

Debt (Tables)

Debt (Tables)	9 Months Ended
	Sep. 30, 2018
Debt Disclosure [Abstract]
Summary of Composition of Debt	The following table presents the composition of debt as of September 30, 2018 and December 31, 2017 (in thousands): September 30, 2018 December 31, 2017 Outstanding principal $ 30,000 $ 30,000 Accrued final payment fees 1,377 940 Less debt discounts (1,179 ) (1,384 ) Total long-term debt, net 30,198 29,556 Less current portion of long-term debt (5,000 ) - Long-term debt, net $ 25,198 $ 29,556
Summary of Future Principal Payments	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

Convertible Preferred Stock a_2

Convertible Preferred Stock and Stockholders' Deficit (Tables)	9 Months Ended
	Sep. 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 September 30, 2018 and December 31, 2017 (in thousands): September 30, 2018 December 31, 2017 Shares of common stock issued 17,579 231 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 Common stock warrants outstanding 105 - Stock options outstanding 2,873 2,444 Restricted stock units outstanding 38 - Shares available for grant under stock incentive plan 1,323 246 Shares available for sale under employee stock purchase plan 244 - Total shares of common stock issued and reserved for issuance 22,162 14,040 ___________________________ (1) Shares of Series A-2 convertible preferred stock converted 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 converted 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 converted to common stock at a ratio of 0.05071 shares of common stock per share of Series C convertible preferred stock.
Summary of Outstanding Common Stock Warrants	The following table summarizes the Company’s outstanding common stock warrants as of September 30, 2018: Warrants Outstanding (in thousands) Exercise Price Expiration Date 14 $ 19.55 Dec-2022 30 $ 9.73 Feb-2021 20 $ 9.73 Aug-2023 20 $ 9.73 Mar-2024 21 $ 9.73 Dec-2024 105

Loss Per Share (Tables)

Loss Per Share (Tables)	9 Months Ended
	Sep. 30, 2018
Earnings Per Share [Abstract]
Schedule of Potentially Dilutive Securities Outstanding Excluded from Diluted Loss Per Share Calculation	The following potentially dilutive securities outstanding as of September 30, 2018 and 2017 have been excluded from the denominator of the diluted loss per share of common stock outstanding calculation (in thousands): September 30, 2018 2017 Stock options 2,873 2,305 Non-vested restricted stock awards 7 15 Non-vested restricted stock units 38 - Convertible preferred stock warrants - 85 Common stock warrants 105 - Shares of convertible preferred stock “as-converted” - 10,994

Share-Based Compensation (Table

Share-Based Compensation (Tables)	9 Months Ended
	Sep. 30, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Summary of Share-Based Compensation Expense	The amount of share-based compensation expense recognized by the Company by location in its statements of operations for the three and nine months ended September 30, 2018 and 2017 is as follows (in thousands): Three Months ended September 30, Nine Months ended September 30, 2018 2017 2018 2017 Cost of revenues $ 6 $ 5 $ 15 $ 12 Sales and marketing 709 38 828 94 General and administrative 273 40 415 148 Research and development 40 14 106 41 Total $ 1,028 $ 97 $ 1,364 $ 295
Summary of Stock Option Activity	The following table summarizes the Company’s stock option activity for the nine months ended September 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 535 $ 7.19 Exercised (29 ) $ 1.58 Forfeited (77 ) $ 3.13 Outstanding at September 30, 2018 2,873 $ 3.27 7.2 $ 82,739 Exercisable at September 30, 2018 1,642 $ 2.23 5.9 $ 48,967 Vested and expected to vest at September 30, 2018 2,873 $ 3.27 7.2 $ 82,739
Summary of Weighted-average Inputs and Assumptions used to Estimate Grant-date Fair Value of Stock Options	For the nine months ended September 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 $ 7.19 Exercise price $ 7.19 Expected term (in years) 6.0 Risk-free interest rate 2.7 % Expected volatility 65.6 % Dividend yield 0 %
Summary of Restricted Stock Award and Restricted Stock Unit Activity	The following table summarizes the Company’s restricted stock award and restricted stock unit activity for the nine months ended September 30, 2018: Non-vested Restricted Stock Awards (in thousands) Weighted- average Grant-date Fair Value Non-vested Restricted Stock Units (in thousands) Weighted- average Grant-date Fair Value Non-vested at December 31, 2017 16 $ 2.32 - $ - Granted - $ - 38 $ 25.92 Vested (9 ) $ 2.32 - $ - Non-vested at September 30, 2018 7 $ 2.32 38 $ 25.92

Geographical Segment Informat_2

Geographical Segment Information (Tables)	9 Months Ended
	Sep. 30, 2018
Segments Geographical Areas [Abstract]
Summary of Revenue Generated in Geographic Regions for Years Indicated	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 September 30, 2018 2017 Amount % of Revenues Amount % of Revenues United States $ 13,518 98 % $ 10,398 99 % International 219 2 % 93 1 % Total revenues $ 13,737 100 % $ 10,491 100 % Revenues by Geography Nine Months ended September 30, 2018 2017 Amount % of Revenues Amount % of Revenues United States $ 36,388 98 % $ 28,017 99 % International 753 2 % 308 1 % Total revenues $ 37,141 100 % $ 28,325 100 %

Description of Business - Addit

Description of Business - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	Jul. 02, 2018	Sep. 30, 2018	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Description Of Business [Line Items]
IPO closing date	Jul. 2, 2018
Net proceeds from initial public offering			$ 99,998
Common stock, par value per share		$ 0.01	$ 0.01		$ 0.01
Common stock, shares authorized for issuance		200,000,000	200,000,000		200,000,000
Preferred stock, shares authorized for issuance		10,000,000	10,000,000		10,000,000
Preferred stock, par value per share		$ 0.01	$ 0.01		$ 0.01
Cash and cash equivalents		$ 106,760	$ 106,760		$ 29,147
Accumulated deficit		214,900	214,900		196,946
Cash flows from operating activities			18,315	$ 11,412	$ 11,100
$35.0 Million Credit Facility | Oxford Finance LLC
Description Of Business [Line Items]
Borrowings outstanding under credit facility		$ 30,000	$ 30,000
Credit facility maturity date			Mar. 1, 2022
Common Stock
Description Of Business [Line Items]
Common stock shares issued and sold		6,325,000
Convertible preferred stock converted into common stock		10,994,000
Initial Public Offering
Description Of Business [Line Items]
Net proceeds from initial public offering	$ 96,500
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 | Common Stock
Description Of Business [Line Items]
Common stock shares issued and sold	6,325,000
Issuance price per share	$ 17
Convertible preferred stock converted into common stock	11,000,000

Basis of Presentation - Additio

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

Recent Accounting Pronounceme_2

Recent Accounting Pronouncements - Additional Information (Details) $ in Millions	9 Months Ended
	Sep. 30, 2018USD ($)
New Accounting Pronouncements And Changes In Accounting Principles [Abstract]
Aggregate future minimum lease payments	$ 1.3
Current non-cancelable office lease, expiration date	2,021

Fair Value Measurement and Fi_3

Fair Value Measurement and Financial Instruments - Schedule of Carrying Amounts and Fair Values of Financial Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Carrying Amount | Convertible preferred sock warrant liability
Liabilities
Total liabilities		$ 478
Fair Value | Convertible preferred sock warrant liability
Liabilities
Total liabilities		478
Money market funds | Carrying Amount
Assets
Total assets	$ 86,605	11,149
Money market funds | Fair Value
Assets
Total assets	86,605	11,149
Quoted Prices In Active Markets (Level 1) | Money market funds
Assets
Total assets	$ 86,605	11,149
Significant Unobservable Inputs (Level 3) | Convertible preferred sock warrant liability
Liabilities
Total liabilities		$ 478

Fair Value Measurement and Fi_4

Fair Value Measurement and Financial Instruments - Summary of Fair Value Inputs and Assumptions (Details)	Jul. 02, 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	26.41	9.57
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	26.41	11.01
Exercise Price | Series E
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Fair value assumption	19.55	19.55
Exercise Price | Series F
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Fair value assumption	9.73	9.73
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
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 Fi_5

Fair Value Measurement and Financial Instruments - Summary of Changes in Instruments Measured on Recurring Basis (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2018USD ($)
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Balance at December 31, 2017	$ 478
Change in fair value	1,396
Reclassification to additional paid in capital	(1,874)
Balance at September 30, 2018	$ 0

Accounts Receivable - Compositi

Accounts Receivable - Composition of Accounts Receivable, Net (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Receivables [Abstract]
Gross accounts receivable - trade	$ 5,742	$ 4,684
Less: Allowances for doubtful accounts	(459)	(417)
Accounts receivable, net	$ 5,283	$ 4,267

Property and Equipment and Ca_3

Property and Equipment and Capitalized Software - Summary of Composition of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 3,318	$ 3,190
Less: Accumulated depreciation	(1,975)	(1,831)
Property and equipment, net	1,343	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	937	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	$ 1,293	$ 1,447

Property and Equipment and Ca_4

Property and Equipment and Capitalized Software - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Property Plant And Equipment [Line Items]
Depreciation and amortization expense	$ 0.2	$ 0.1	$ 0.7	$ 0.5
Other Assets [Member]
Property Plant And Equipment [Line Items]
Capitalized software cost, net	$ 0.7		$ 0.7		$ 0.4

Accrued Expenses - Summary of C

Accrued Expenses - Summary of Composition of Accrued Expenses (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Payables And Accruals [Abstract]
Compensation and related benefits	$ 3,402	$ 4,465
Consulting and professional fees	833	461
Research and development expenses	209	497
Sales and marketing expenses	148	620
Warranty	650	570
Sales tax payable	376	322
Interest payable	237	188
Other	528	388
Accrued expenses	$ 6,383	$ 7,511

Debt - Summary of Composition o

Debt - Summary of Composition of Debt (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Debt Disclosure [Abstract]
Outstanding principal	$ 30,000	$ 30,000
Accrued final payment fees	1,377	940
Less debt discounts	(1,179)	(1,384)
Total long-term debt, net	30,198	29,556
Less current portion of long-term debt	(5,000)	0
Long-term debt, net	$ 25,198	$ 29,556

Debt - Additional Information (

Debt - Additional Information (Details) - USD ($) $ / shares in Units, shares in Thousands	Feb. 28, 2017	Mar. 31, 2017	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Debt Instrument [Line Items]
Interest expense			$ 928,000	$ 807,000	$ 2,749,000	$ 2,068,000
Cash interest expense			700,000	500,000	2,100,000	1,600,000
Non-cash interest expense			200,000	$ 300,000	$ 600,000	$ 500,000
Debt instrument, final payment fee		$ 1,000,000
$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
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. 1, 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 | Common Stock
Debt Instrument [Line Items]
Warrants to purchase shares			20,303		20,303
Warrants, exercise price			$ 9.73		$ 9.73
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 | Common Stock
Debt Instrument [Line Items]
Warrants to purchase shares			20,303		20,303
Warrants, exercise price			$ 9.73		$ 9.73
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
Notification period for lenders to borrow loan upon achieving required revenue milestone					60 days
Line of credit facility additional borrowing capacity			$ 5,000,000		$ 5,000,000
$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 Princ

Debt - Schedule of Future Principal Payments (Details) - USD ($) $ in Thousands	Sep. 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]
2,019	7,500
2,020	10,000
2,021	10,000
2,022	2,500
Total principal payments	$ 30,000

Convertible Preferred Stock a_3

Convertible Preferred Stock and Stockholders' Deficit - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	Jul. 02, 2018	Sep. 30, 2018	Sep. 30, 2018	Dec. 31, 2017
Stockholders Deficit [Line Items]
IPO closing date	Jul. 2, 2018
Net proceeds from initial public offering			$ 99,998
Common stock, par value per share		$ 0.01	$ 0.01	$ 0.01
Common stock, shares authorized for issuance		200,000,000	200,000,000	200,000,000
Preferred stock, shares authorized for issuance		10,000,000	10,000,000	10,000,000
Preferred stock, par value per share		$ 0.01	$ 0.01	$ 0.01
Common stock, shares issued		17,579,000	17,579,000	231,000
Common stock, shares outstanding		17,579,000	17,579,000	231,000
Common Stock
Stockholders Deficit [Line Items]
Common stock shares issued and sold		6,325,000
Convertible preferred stock converted into common stock		10,994,000
Initial Public Offering
Stockholders Deficit [Line Items]
Net proceeds from initial public offering	$ 96,500
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 | Common Stock
Stockholders Deficit [Line Items]
Common stock shares issued and sold	6,325,000
Issuance price per share	$ 17
Convertible preferred stock converted into common stock	11,000,000

Convertible Preferred Stock a_4

Convertible Preferred Stock and Stockholders' Deficit - Summary of Common Stock Issued and Reserved for Issuance (Details) - shares	Sep. 30, 2018	Jul. 31, 2018	Dec. 31, 2017
Stockholders Deficit [Line Items]
Shares of common stock issued	17,579,000		231,000
Shares of common stock reserved for issuance for:
Total shares of common stock issued and reserved for issuance	22,162,000		14,040,000
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
Common Stock Warrants Outstanding
Shares of common stock reserved for issuance for:
Shares of common stock reserved for issuance	105,000
Warrants Issuable Upon Term C Loan Borrowing
Shares of common stock reserved for issuance for:
Shares of common stock reserved for issuance			20,000
Shares Available for Sales Under Employee Stock Purchase Plan
Shares of common stock reserved for issuance for:
Shares of common stock reserved for issuance	244,000	200,000
Stock Options Outstanding
Shares of common stock reserved for issuance for:
Shares of common stock reserved for issuance	2,873,000		2,444,000
Shares Available for Grant Under Stock Incentive Plan
Shares of common stock reserved for issuance for:
Shares of common stock reserved for issuance	1,323,000		246,000
Restricted Stock Units Outstanding
Shares of common stock reserved for issuance for:
Shares of common stock reserved for issuance	38,000

Convertible Preferred Stock a_5

Convertible Preferred Stock and Stockholders' Deficit - Summary of Common Stock Issued and Reserved for Issuance (Parenthetical) (Details)	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Series A-2 Convertible Preferred Stock
Stockholders Deficit [Line Items]
Convertible preferred stock converted to common stock, ratio	3.539%	3.539%
Series B Convertible Preferred Stock
Stockholders Deficit [Line Items]
Convertible preferred stock converted to common stock, ratio	4.103%	4.103%
Series C Convertible Preferred Stock
Stockholders Deficit [Line Items]
Convertible preferred stock converted to common stock, ratio	5.071%	5.071%

Convertible Preferred Stock a_6

Convertible Preferred Stock and Stockholders' Deficit - Summary of Outstanding Common Stock Warrants (Details) shares in Thousands	9 Months Ended
	Sep. 30, 2018$ / sharesshares
Class Of Warrant Or Right [Line Items]
Warrants Outstanding	105
Exercise Price $19.55
Class Of Warrant Or Right [Line Items]
Warrants Outstanding	14
Exercise Price | $ / shares	$ 19.55
Expiration Date	2022-12
Exercise Price $9.73
Class Of Warrant Or Right [Line Items]
Warrants Outstanding	30
Exercise Price | $ / shares	$ 9.73
Expiration Date	2021-02
Exercise Price $9.73
Class Of Warrant Or Right [Line Items]
Warrants Outstanding	20
Exercise Price | $ / shares	$ 9.73
Expiration Date	2023-08
Exercise Price $9.73
Class Of Warrant Or Right [Line Items]
Warrants Outstanding	20
Exercise Price | $ / shares	$ 9.73
Expiration Date	2024-03
Exercise Price $9.73
Class Of Warrant Or Right [Line Items]
Warrants Outstanding	21
Exercise Price | $ / shares	$ 9.73
Expiration Date	2024-12

Loss Per Share - Schedule of Po

Loss Per Share - Schedule of Potentially Dilutive Securities Outstanding Excluded from Diluted Loss Per Share Calculation (Details) - shares shares in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 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	2,873	2,305
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	7	15
Non-vested Restricted Stock Units
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities outstanding excluded from diluted loss per share	38
Common Stock Warrants
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities outstanding excluded from diluted loss per share	105
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		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

Share-Based Compensation - Summ

Share-Based Compensation - Summary of Share-Based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total	$ 1,028	$ 97	$ 1,364	$ 295
Cost of Revenues
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total	6	5	15	12
Selling and Marketing
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total	709	38	828	94
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total	273	40	415	148
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total	$ 40	$ 14	$ 106	$ 41

Share-Based Compensation - Addi

Share-Based Compensation - Additional Information (Details) $ / shares in Units, $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	Apr. 30, 2018USD ($)Installment$ / sharesshares	Sep. 30, 2018USD ($)shares	Sep. 30, 2017USD ($)	Sep. 30, 2018USD ($)$ / sharesshares	Sep. 30, 2017USD ($)
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation expenses		$ 1,028	$ 97	$ 1,364	$ 295
Unrecognized compensation cost related to non-vested stock options		2,900		$ 2,900
Weighted-average grant-date fair value of stock options granted | $ / shares				$ 4.38
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		1,000	100	$ 1,300	200
Non-vested awards not yet recognized weighted-average period for recognition				3 years 2 months 12 days
Restricted Stock Awards and Restricted Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation expenses		100	$ 100	$ 100	$ 100
Non-vested awards not yet recognized weighted-average period for recognition				3 years 7 months 6 days
Unrecognized compensation cost related to non-vested restricted stock		$ 900		$ 900
Fair value of restricted stock vested				$ 200
2018 Equity 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		1,300,000		1,300,000
2018 Equity 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%
2018 Equity Incentive Plan | Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares authorized for issuance | shares		1,400,000		1,400,000
Maximum contractual term of stock options				10 years
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		0		0
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 - Su_2

Share-Based Compensation - Summary of Stock Option Activity (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	9 Months Ended
	Sep. 30, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted-average Exercise Price per Option, Granted	$ 7.19
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	535
Number of Shares under Option, Exercised	(29)
Number of Shares under Option, Forfeited	(77)
Number of Shares under Option, Outstanding, Ending balance	2,873
Number of Shares under Option, Exercisable	1,642
Number of Shares under Option, Vested and expected to vest	2,873
Weighted-average Exercise Price per Option, Outstanding, Beginning balance	$ 2.39
Weighted-average Exercise Price per Option, Granted	7.19
Weighted-average Exercise Price per Option, Exercised	1.58
Weighted-average Exercise Price per Option, Forfeited	3.13
Weighted-average Exercise Price per Option, Outstanding, Ending balance	3.27
Weighted-average Exercise Price per Option, Exercisable	2.23
Weighted-average Exercise Price per Option, Vested and expected to vest	$ 3.27
Weighted-average Remaining Contractual Life, Outstanding	7 years 2 months 12 days
Weighted-average Remaining Contractual Life, Exercisable	5 years 10 months 24 days
Weighted-average Remaining Contractual Life, Vested and expected to vest	7 years 2 months 12 days
Aggregate Intrinsic Value, Outstanding	$ 82,739
Aggregate Intrinsic Value, Exercisable	48,967
Aggregate Intrinsic Value, Vested and expected to vest	$ 82,739

Share-Based Compensation - Su_3

Share-Based Compensation - Summary of Weighted-average Inputs and Assumptions used to Estimate Grant-date Fair Value of Stock Options (Details)	9 Months Ended
	Sep. 30, 2018$ / shares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Estimated fair value of common stock	$ 7.19
Weighted-average Exercise Price per Option, Granted	$ 7.19
Expected term (in years)	6 years
Risk-free interest rate	2.70%
Expected volatility	65.60%
Dividend yield	0.00%

Share-Based Compensation - Su_4

Share-Based Compensation - Summary of Restricted Stock Award and Restricted Stock Unit Activity (Details) shares in Thousands	9 Months Ended
	Sep. 30, 2018$ / sharesshares
Restricted Stock Awards [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Non-vested, Beginning balance | shares	16
Vested | shares	(9)
Non-vested, Ending balance | shares	7
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
Non-vested Restricted Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Granted | shares	38
Non-vested, Ending balance | shares	38
Weighted-average Grant-date Fair Value, Granted | $ / shares	$ 25.92
Weighted-average Grant-date Fair Value, Non-vested, Ending balance | $ / shares	$ 25.92

Employee Benefit Plans - Additi

Employee Benefit Plans - Additional Information (Details) - shares shares in Thousands	1 Months Ended	9 Months Ended
	Jul. 31, 2018	Sep. 30, 2018
Defined Benefit Plan Disclosure [Line Items]
Defined contribution retirement plan, plan name		401(k) plan
2018 ESPP
Defined Benefit Plan Disclosure [Line Items]
Shares of common stock reserved for issuance	200	244
Common stock purchase price, discount rate	15.00%
Maximum | 2018 ESPP
Defined Benefit Plan Disclosure [Line Items]
Period of automatic annual increase in the share reserve	10 years
401(k) Plan
Defined Benefit Plan Disclosure [Line Items]
Defined contribution retirement plan, maximum employee contribution deferred		100.00%

Commitments and Contingencies -

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

Geographical Segment Informat_3

Geographical Segment Information - Additional Information (Details)	9 Months Ended
	Sep. 30, 2018Segment
Segments Geographical Areas [Abstract]
Number of operating business segment	1

Geographical Segment Informat_4

Geographical Segment Information - Summary of Revenue Generated in Geographic Regions for Years Indicated (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting Information [Line Items]
Revenues	$ 13,737	$ 10,491	$ 37,141	$ 28,325
Revenues | Geographic Concentration
Segment Reporting Information [Line Items]
Revenues	$ 13,737	$ 10,491	$ 37,141	$ 28,325
Percentage of Revenues	100.00%	100.00%	100.00%	100.00%
Revenues | United States | Geographic Concentration
Segment Reporting Information [Line Items]
Revenues	$ 13,518	$ 10,398	$ 36,388	$ 28,017
Percentage of Revenues	98.00%	99.00%	98.00%	99.00%
Revenues | International | Geographic Concentration
Segment Reporting Information [Line Items]
Revenues	$ 219	$ 93	$ 753	$ 308
Percentage of Revenues	2.00%	1.00%	2.00%	1.00%