Venus Concept (VERO) 10-K 5 Mar 18 2017 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2017	Feb. 26, 2018
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	FY
Trading Symbol	HAIR
Entity Registrant Name	Restoration Robotics, Inc.
Entity Central Index Key	1,409,269
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding	28,940,282
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float		$ 106,858,458

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
CURRENT ASSETS:
Cash and cash equivalents	$ 23,545	$ 11,906
Accounts receivable, net	3,864	2,481
Inventory	2,761	2,742
Prepaid expenses and other current assets	1,562	810
Total current assets	31,732	17,939
Property and equipment, net	1,138	1,459
Other assets	100	100
TOTAL ASSETS	32,970	19,498
CURRENT LIABILITIES:
Accounts payable	2,044	1,740
Accrued and other liabilities	2,755	2,438
Deferred revenue	1,517	1,423
Current portion of long-term debt, net of discount of $270 and $551 as of December 31, 2017 and 2016	7,730	7,449
Total current liabilities	14,046	13,050
Other long-term liabilities	459	563
Preferred stock warrant liabilities		693
Long-term debt, net of discount of $29 and $299 as of December 31, 2017 and 2016	5,271	13,001
TOTAL LIABILITIES	19,776	27,307
Commitments and Contingencies (Note 6)
Convertible preferred stock, $0.0001 par value; no and 236,154,444 shares authorized as of December 31, 2017 and 2016; no and 21,142,295 shares issued and outstanding as of December 31, 2017 and 2016; aggregate liquidation preference of no and $142,231 as of December 31, 2017 and 2016		135,735
STOCKHOLDERS’ EQUITY (DEFICIT):
Preferred stock, $0.0001 par value: 10,000,000 and no shares authorized as of December 31, 2017 and 2016; no shares issued and outstanding as of December 31, 2017 and 2016
Common stock, $0.0001 par value: 300,000,000 and 350,490,000 shares authorized as of December 31, 2017 and 2016; 28,940,282 and 1,615,495 shares issued and outstanding as of December 31, 2017 and 2016	3
Additional paid-in capital	177,757	3,087
Accumulated other comprehensive income (loss)	(79)	14
Accumulated deficit	(164,487)	(146,645)
TOTAL STOCKHOLDERS’ EQUITY (DEFICIT)	13,194	(143,544)
TOTAL LIABILITIES, CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS’ EQUITY (DEFICIT)	$ 32,970	$ 19,498

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Statement Of Financial Position [Abstract]
Current portion of long-term debt, discount	$ 270	$ 551
Long-term debt, discount	$ 29	$ 299
Convertible preferred stock at liquidation preference par value	$ 0.0001	$ 0.0001
Convertible preferred stock, shares authorized	0	236,154,444
Convertible preferred stock, shares issued	0	21,142,295
Convertible preferred stock, shares outstanding	0	21,142,295
Aggregate liquidation preference	$ 0	$ 142,231
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	10,000,000	0
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	300,000,000	350,490,000
Common stock, shares issued	28,940,282	1,615,495
Common stock, shares outstanding	28,940,282	1,615,495

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Consolidated Statements of Operations Data:
Revenue, net	$ 21,297	$ 15,600	$ 17,230
Cost of revenue	12,150	10,431	12,513
Gross profit	9,147	5,169	4,717
Operating expenses:
Research and development	7,135	7,474	7,399
Sales and marketing	14,390	12,483	14,587
General and administrative	4,904	4,144	3,256
Total operating expenses	26,429	24,101	25,242
Loss from operations	(17,282)	(18,932)	(20,525)
Other income (expense), net:
Interest expense	(2,027)	(2,483)	(2,892)
Gain on sale of investment	1,851
Other income (expense)	(328)	(431)	446
Total other income (expense), net	(504)	(2,914)	(2,446)
Net loss before provision for income taxes	(17,786)	(21,846)	(22,971)
Provision for income taxes	56
Net loss	$ (17,842)	$ (21,846)	$ (22,971)
Net loss per share, basic and diluted	$ (2.42)	$ (13.54)	$ (14.70)
Weighted-average shares used in computing net loss per share, basic and diluted	7,382,715	1,612,933	1,562,829

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (17,842)	$ (21,846)	$ (22,971)
Other comprehensive income (loss):
Cumulative translation adjustment	(93)		14
Comprehensive loss	$ (17,935)	$ (21,846)	$ (22,957)

Consolidated Statement of Conve

Consolidated Statement of Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit	Convertible Preferred Stock
Beginning balance, value at Dec. 31, 2014						$ 119,487
Beginning balance, shares at Dec. 31, 2014						18,662,525
Beginning balance, value at Dec. 31, 2014	$ (99,807)		$ 2,021		$ (101,828)
Beginning balance, shares at Dec. 31, 2014		1,515,384
Issuance of common stock pursuant to stock option exercises of vested options	$ 111		111
Issuance of common stock pursuant to stock option exercises of vested options, shares	79,893	79,893
Issuance of Series C convertible preferred stock for cash, net of issuance costs, value						$ 4,175
Issuance of Series C convertible preferred stock for cash, net of issuance costs, shares						674,252
Vesting of shares purchased under an early exercise of stock options	$ 19		19
Stock-based compensation	429		429
Other comprehensive income (loss)	14			$ 14
Net loss	(22,971)				(22,971)
Ending balance, value at Dec. 31, 2015						$ 123,662
Ending balance, shares at Dec. 31, 2015						19,336,777
Ending balance, value at Dec. 31, 2015	(122,205)		2,580	14	(124,799)
Ending balance, shares at Dec. 31, 2015		1,595,277
Issuance of common stock pursuant to stock option exercises of vested options	$ 41		41
Issuance of common stock pursuant to stock option exercises of vested options, shares	20,218	20,218
Issuance of Series C convertible preferred stock for cash, net of issuance costs, value						$ 12,073
Issuance of Series C convertible preferred stock for cash, net of issuance costs, shares						1,805,518
Stock-based compensation	$ 466		466
Net loss	(21,846)				(21,846)
Ending balance, value at Dec. 31, 2016	$ 135,735					$ 135,735
Ending balance, shares at Dec. 31, 2016	21,142,295					21,142,295
Ending balance, value at Dec. 31, 2016	$ (143,544)		3,087	14	(146,645)
Ending balance, shares at Dec. 31, 2016		1,615,495
Issuance of common stock pursuant to stock option exercises of vested options	$ 43		43
Issuance of common stock pursuant to stock option exercises of vested options, shares	21,843	21,843
Issuance of Series C convertible preferred stock for cash, net of issuance costs, value						$ 10,209
Issuance of Series C convertible preferred stock for cash, net of issuance costs, shares						1,529,306
Stock-based compensation	$ 465		465
Adjustment for fractional shares from reverse stock split, shares		137
Reclassification of preferred stock warrant liabilities to additional paid in capital	1,080		1,080
Conversion of convertible notes to common stock, value	5,027		5,027
Conversion of convertible notes to common stock, shares		718,184
Conversion of preferred stock to common stock upon initial public offering, value	145,944	$ 3	145,941			$ (145,944)
Conversion of preferred stock to common stock upon initial public offering, shares		22,671,601				(22,671,601)
Issuance of common stock in connection with initial public offering, net of issuance costs, value	22,114		22,114
Issuance of common stock in connection with initial public offering, net of issuance costs, shares		3,897,910
Issuance of common stock upon exercise of common stock warrants, shares		15,112
Other comprehensive income (loss)	(93)			(93)
Net loss	$ (17,842)				(17,842)
Ending balance, shares at Dec. 31, 2017	0
Ending balance, value at Dec. 31, 2017	$ 13,194	$ 3	$ 177,757	$ (79)	$ (164,487)
Ending balance, shares at Dec. 31, 2017		28,940,282

Consolidated Statement of Conv7

Consolidated Statement of Convertible Preferred Stock and Stockholders' Equity (Deficit) (Parenthetical) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)
Issuance of common stock in connection with initial public offering, issuance costs	$ 5,171
Convertible Preferred Stock
Issuance of Series C convertible preferred stock for cash, issuance costs	$ 726

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (17,842)	$ (21,846)	$ (22,971)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	574	654	860
Loss on disposal of property and equipment	34	46
Amortization of debt issuance costs	551	737	1,209
Stock-based compensation	465	466	429
Changes in fair value of preferred stock warrant liabilities	387	346	(578)
Gain on sale of investment	(1,851)
Non-cash interest expense on convertible notes	27
Changes in operating assets and liabilities:
Accounts receivable	(1,383)	(987)	3,501
Inventory	(19)	2,892	(3,369)
Prepaid expenses and other assets	(752)	324	377
Accounts payable	246	709	(1,929)
Accrued and other liabilities	307	495	(1,647)
Net cash used in operating activities	(19,256)	(16,164)	(24,118)
CASH FLOWS FROM INVESTING ACTIVITIES:
Proceeds from sale of property and equipment		2
Proceeds from sale of investment	1,851
Purchases of property and equipment	(229)	(1,173)	(456)
Net cash provided by (used in) investing activities	1,622	(1,171)	(456)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of common stock upon initial public offering, net	22,114
Proceeds from convertible notes	5,000
Proceeds from exercised stock options	43	41	111
Proceeds from long-term debt, net			19,601
Principal payments on long-term debt	(8,000)	0	(15,000)
Net cash provided by financing activities	29,366	12,114	8,887
NET INCREASE (DECREASE) IN CASH, CASH EQUIVALENTS AND RESTRICTED CASH	11,732	(5,221)	(15,687)
Effect of exchange rate changes on cash, cash equivalents and restricted cash	(93)		14
CASH, CASH EQUIVALENTS AND RESTRICTED CASH — Beginning of period	12,006	17,227	32,900
CASH, CASH EQUIVALENTS AND RESTRICTED CASH — End of period	23,645	12,006	17,227
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION:
Cash paid for income taxes	28	56	61
Cash paid for interest	1,497	1,738	1,452
SUPPLEMENTAL DISCLOSURES OF NON-CASH INVESTING AND FINANCING INFORMATION:
Vesting of shares purchased under an early exercise of stock options			19
Issuance of preferred stock warrants in connection with long-term debt			256
Conversion of preferred stock into common stock	145,944
Reclassification of preferred stock warrant liabilities to equity	1,080
Conversion of convertible notes and accrued interest into common stock	5,027
Non-cash lease incentive			16
Series C Preferred Stock
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of Series C convertible preferred stock, net	$ 10,209	$ 12,073	$ 4,175

Nature of Operations

Nature of Operations	12 Months Ended
	Dec. 31, 2017
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Nature of Operations	1. Nature of Operations Restoration Robotics, Inc. is a medical device company incorporated in the state of Delaware on November 22, 2002 and headquartered in San Jose, California. The Company develops an image-guided robotic system that enables follicular unit extraction (FUE) for use in the field of hair transplantation and markets the ARTAS® Robotic System in the United States and other countries. In these notes to the audited consolidated financial statements, the “Company,” “Restoration Robotics,” “we,” “us,” and “our” refers to Restoration Robotics, Inc. and its subsidiaries on a consolidated basis. Initial Public Offering On October 11, 2017, the Company’s Registration Statement on Form S-1 (File No. 333-220303) relating to the initial public offering (IPO) of its common stock was declared effective by the Securities and Exchange Commission (SEC). Pursuant to such Registration Statement, the Company completed its IPO of 3,897,910 shares of its common stock (inclusive of 322,910 shares of common stock from the subsequent exercise of the over-allotment option granted to the underwriters) at a price of $7.00 per share for aggregate cash proceeds of approximately $22,114, after deducting underwriter discounts and commissions, and offering costs of $5,171. Immediately prior to the closing of the IPO, all outstanding shares of convertible preferred stock converted into 22,671,601 shares of common stock and all the outstanding convertible preferred stock warrants converted into common stock warrants resulting in the reclassification of our preferred stock warrant liabilities to additional paid-in capital. In addition, the principal and accrued interest on the outstanding Convertible Notes converted into 718,184 shares of common stock. The IPO closed on October 16, 2017. Following the filing of the Restated Certificate of Incorporation of the Company on October 16, 2017, the number of shares of capital stock the Company is authorized to issue is 310,000,000 shares, of which 300,000,000 shares may be common stock and 10,000,000 shares may be preferred stock. Both the common stock and the preferred stock have a par value of $0.0001 per share. Reverse Stock Split On September 15, 2017, the Company effected a 1-for-10 reverse stock split of its common stock. Upon the effectiveness of the reverse stock split, (i) every 10 shares of outstanding common stock were combined into one share of common stock, (ii) the number of shares of common stock for which each outstanding option to purchase common stock is exercisable was proportionately decreased on a 1-for-10 basis, (iii) the exercise price of each outstanding option to purchase common stock was proportionally increased on a l-for-10 basis, and (iv) the conversion ratio for each share of outstanding preferred stock which is convertible into our common stock was proportionately reduced on a 1-for-10 basis. All of the outstanding common stock share numbers (including shares of common stock into which our outstanding convertible preferred stock shares are convertible), share prices, exercise prices and per share amounts have been adjusted in these consolidated statements, on a retroactive basis, to reflect this l-for-10 reverse stock split for all periods presented. The par value per share and the authorized number of shares of common stock and convertible preferred stock were not adjusted as a result of the reverse stock split.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Liquidity These consolidated financial statements are prepared on a going concern basis that contemplates the realization of assets and extinguishment of liabilities in the normal course of business. The Company has incurred net operating losses and negative cash flows from operations since inception. As of December 31, 2017 and 2016, the Company has an accumulated deficit of $164,487 and $146,645 and, as of such dates, did not have sufficient capital to fund its planned operations. As a result of the Company’s recurring losses from operations and negative cash flows, the Company’s independent registered public accounting firm included an explanatory paragraph in its current report on the Company’s consolidated financial statements that such factors raise substantial doubt about the Company’s ability to continue as a going concern. Management plans to manage expenses and obtain additional funds through a combination of equity and debt financing. The Company will need to raise further capital in the future to service its debt or fund its operations until the time it can sustain positive cash flows. There can be no assurance that the Company will be successful in raising additional capital or that such capital, if available, will be on terms that are acceptable to the Company. If the Company is unable to raise sufficient additional capital, it may be compelled to reduce the scope of its operations and planned capital expenditures or sell certain assets, including intellectual property assets. The accompanying consolidated financial statements have been prepared on a going concern basis, which contemplates the realization of assets and the satisfaction of liabilities in the normal course of business, and, as such, the consolidated financial statements do not include any adjustments relating to the recoverability and classification of recorded asset amounts or amounts and classification of liabilities that might be necessary should the Company be unable to continue in existence. Basis of Presentation The accompanying consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United States of America (U.S. GAAP). The accompanying consolidated financial statements include the accounts of Restoration Robotics, Inc. and its wholly owned subsidiaries. Principles of Consolidation The accompanying consolidated financial statements include the accounts of Restoration Robotics, Inc. and its wholly owned subsidiaries, which are located in the United States, United Kingdom, Spain, Hong Kong and South Korea. All significant intercompany accounts and transactions have been eliminated in consolidation. Use of Estimates The preparation of the consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the date of the consolidated financial statements and the reported amounts of revenue and expenses during the reporting period. Significant estimates and assumptions made in the accompanying consolidated financial statements include, but are not limited to revenue recognition, the fair value of common stock, the fair value of preferred stock warrant liabilities, and the recoverability of the Company’s net deferred tax assets, and related valuation allowance. The Company evaluates its estimates and assumptions on an ongoing basis using historical experience and other factors and adjusts those estimates and assumptions when facts and circumstances dictate. Actual results could materially differ from those estimates. Segments Operating segments are defined as components of an entity for which separate financial information is available and that is regularly reviewed by the Chief Operating Decision Maker (CODM) in deciding how to allocate resources to an individual segment and in assessing performance. The Company's CODM is its Chief Executive Officer. The Company has determined it operates in a single operating segment and has one reportable segment, as the CODM reviews financial information presented on a consolidated basis for purposes of making operating decisions, allocating resources, and evaluating financial performance. Foreign Currency The functional currency of the Company’s non-U.S. subsidiaries is the local currency. Asset and liability balances denominated in non-U.S. dollar currencies are translated into U.S. dollars using period-end exchange rates, while revenue and expenses are based upon the exchange rate at the time of the transaction, if known, or at the average rate for the period. Differences are included in stockholders’ equity (deficit) as a component of accumulated other comprehensive loss. Financial assets and liabilities denominated in currencies other than the functional currency are recorded at the exchange rate at the time of the transaction and subsequent gains and losses related to changes in the foreign currency are included in other income (expense), net in the accompanying consolidated statements of operations. The net foreign transaction gain or losses were insignificant for all periods presented. Cash and Cash Equivalents The Company considers all highly liquid investments with an original maturity of three months or less from the date of purchase to be cash equivalents. Cash and cash equivalents consists primarily of funds invested in readily available checking and savings accounts, investments in money market funds and short-term time deposits. The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the balance sheets that sum to the total of the same amounts shown in the statements of cash flows. December 31, 2017 2016 Cash and cash equivalents $ 23,545 $ 11,906 Restricted cash 100 100 Total cash, cash equivalents and restricted cash in the consolidated statements of cash flows $ 23,645 $ 12,006 Restricted Cash As of December 31, 2017 and 2016, the Company was required to hold $100 in a separate money market account as collateral for credit cards. These amounts are recorded in other assets in the accompanying consolidated balance sheets. Concentration of Credit Risk Financial instruments that potentially subject the Company to a concentration of credit risk consist of cash and cash equivalents, restricted cash and accounts receivable. Substantially all of the Company’s cash and cash equivalents and restricted cash are held with two financial institutions, and the account balances exceed the Federal Deposit Insurance Corporation (FDIC) insurance limit. Accounts are insured by the FDIC up to $250 per financial institution. The Company has not experienced any losses in such accounts with these financial institutions. Concentration of Customers For the year ended December 31, 2017, 2016 and 2015, there were no customers accounting for more than 10% of the Company’s revenue. As of December 31, 2017, two customers each accounted for 10% and 11% of the Company’s accounts receivable. As of December 31, 2016, six customers accounted for 10%, 11%, 11%, 11%, 12%, and 13% of the Company’s accounts receivable. Allowance for Doubtful Accounts Accounts receivable do not bear interest and are typically not collateralized. The Company performs ongoing credit evaluations of its customers and maintains reserves for potential credit losses. Accounts receivable are deemed past due in accordance with the contractual terms of the agreement. Accounts are charged against the allowance for doubtful accounts once collection efforts are unsuccessful. Historically, such losses have been within management's expectations. The allowance for doubtful accounts is $229 and $0 at December 31, 2017 and 2016. Investments The Company determines the appropriate designation of its investments as “trading”, “available-for-sale” or “held-to-maturity” based on management’s intent at the time of purchase and reevaluates such designated at each reporting date. For all reporting periods presented, the Company’s investments are designated as available-for-sale. The Company determines any realized gains or losses on the sale of any investments on a specific identification method and records such gains and losses in the accompanying consolidated statements of operations. The Company evaluates its investments periodically for possible other-than-temporary impairment. A decline in fair value below the amortized cost of the investment is considered other-than-temporary impairment if the Company has the intent to sell the investment or it is more likely than not that the Company will be required to sell the investment before recovery of the entire amortized cost basis. In those instances, an impairment charge equal to the difference between the fair value and the amortized cost. Inventory Inventory is stated at the lower of cost or net realizable value and cost is principally determined using the first-in, first-out method. Costs include material, labor and overhead. Inventory that is obsolete or in excess of forecasted usage is written down to its estimated net realizable value based on assumptions about future demand and market conditions. Inventory write-downs are charged to cost of goods sold and a new cost basis for the inventory is established. Concentration of Supplier The Company has a single source supplier manufacturing its system. If the supplier is not able to supply the requested orders, the Company would be unable to continue to derive revenue from the sale of systems until an alternative source is found, which could take a considerable length of time. Property and Equipment Property and equipment are stated at cost, net of accumulated depreciation and amortization. Depreciation and amortization are computed using the straight-line method over the estimated useful lives of the assets, which is between three and five years. Leasehold improvements are amortized over the lesser of the life of the lease or the useful life of the improvements. Maintenance and repairs are charged to expense as incurred. When assets are retired or otherwise disposed of, the cost and accumulated depreciation are removed from the consolidated balance sheet, and any resulting gain or loss is reflected in operations. Impairment of Long-Lived Assets Long-lived assets are reviewed annually for impairment or whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. Recoverability is measured by comparison of the carrying amount to the future net undiscounted cash flows that the assets are expected to generate. If the carrying amount of an asset group exceeds its estimated future cash flows, an impairment charge is recognized in the amount by which the carrying amount of the asset group exceeds the fair value of the asset group. If such assets are considered to be impaired, the impairment to be recognized is measured by the amount by which the carrying amount of the assets exceeds the projected discounted future net cash flows arising from the asset. There has been no impairment of long-lived assets for any of the periods presented. Preferred Stock Warrants Liabilities The Company accounted for its freestanding warrants to purchase shares of convertible preferred stock that are contingently redeemable as liabilities in the consolidated balance sheets at their estimated fair value because these warrants may have obligated the Company to redeem them at some point in the future. At the end of each reporting period, changes in the estimated fair value of the warrants to purchase shares of convertible preferred stock were recorded as other income (expense), net in the consolidated statements of operations. Upon the closing of the IPO (as discussed in Note 1), all outstanding preferred stock warrants were converted into common stock warrants and the liability on the preferred stock warrants was reclassified to additional paid-in capital in stockholders’ equity (deficit) and was no longer subject to remeasurement. Debt Issuance Costs Costs related to the issuance of debt are presented as a direct deduction to the carrying value of the debt and are amortized to interest expense using the effective interest rate method over the term of the related debt. Gain on Sale of Stock Investment In the fourth quarter of 2017, the Company recognized a gain of $1,851 on the sale of stock held in a privately-held company that had been impaired and written-down to nil prior to fiscal year 2014. Revenue Recognition The Company generates revenue from sales of robotic systems and related procedures, and related support and maintenance. The Company derives revenue primarily from two sources: (i) Product revenue, which includes robotic systems sales, installation, software, procedure key and disposable kits; and (ii) Support and maintenance revenue, which includes support, training, and service contracts. Revenue is recognized when all of the following criteria are met: (l) persuasive evidence of an arrangement exists; (2) the product or service has been delivered; (3) the sales price is fixed or determinable; and (4) collection is reasonably assured. The Company defines each of the four criteria above as follows: • Persuasive Evidence of Arrangement Exists . The Company uses purchase orders pursuant to the terms and conditions of a master agreement to support the evidence of an arrangement with distributors and uses purchase agreements as evidence of arrangement with direct customers. • Delivery has Occurred . Provided that all other revenue recognition criteria have been met, for direct sales the Company typically recognizes system revenue upon customer acceptance, or upon shipment for systems sold to distributors, as title and risk of loss are transferred at that time, and there are no further obligations and no rights of return. Procedure revenue is recognized upon shipment of disposable kits and delivery of the ARTAS key. Support and maintenance revenue is recognized over time as the services are delivered. • The Sales Price is Fixed or Determinable . The Company assesses whether the fee is fixed or determinable based on the payment terms associated with the transaction. If the terms are extended beyond the Company’s normal payment terms, the Company will recognize revenue as the payments become due. Payments from distributors are not contingent on the distributors’ receiving payment from the end-users. • Collection is Reasonably Assured . The Company assesses probability of collection on an individual basis based on a number of factors, including the credit-worthiness of the customer and past transaction history with the customer. The Company generally obtains a significant cash deposit from its customers prior to shipment. The Company records its revenue net of sales tax and shipping and handling costs. Incremental direct costs incurred related to the acquisition or origination of a customer contract are expensed as incurred. Multiple Element Arrangements The Company’s offering includes robotic systems containing software components that function together to provide the essential functionality of the product. Therefore, the Company’s hardware products (inclusive of the core software) are considered non-software deliverables and are not subject to industry-specific software revenue recognition guidance. The Company’s typical multiple element arrangement includes robotic systems (including the essential software), procedure key, installation (for direct sales to end-users), product training and service contracts. The Company considers each of these deliverables to be separate units of accounting based on whether the delivered items have stand-alone value. The Company has determined that each unit of accounting has stand-alone value because they are sold separately by the Company or, for hardware products, because the customers can resell them to others on a stand-alone basis. For the arrangements with multiple deliverables, the Company allocates the arrangement fee to each element based upon the relative selling price of such element. When applying the relative selling price method, the Company determines the selling price for each element using vendor-specific objective evidence (VSOE) of selling price, if it exists, or if not, third-party evidence (TPE) of selling price, if it exists. If neither VSOE nor TPE of selling price exist for an element, the Company uses its best estimated selling price (BESP) for that element. The revenue allocated to each element is then recognized when the basic revenue recognition criteria are met for that element. The Company is not able to establish a selling price of its deliverables using VSOE or to determine TPE for its products and services. TPE is determined based on competitor prices for similar deliverables when sold separately. Generally, the Company’s go-to-market strategy differs from that of its peers and its offerings contain a significant level of differentiation such that the comparable pricing of products with similar functionality cannot be obtained. When the Company is unable to establish the selling price of its deliverables using VSOE or TPE, the Company uses BESP in its allocation of arrangement consideration. The objective of BESP is to determine the price at which the Company would transact a sale if the product or service were sold on a stand-alone basis. The Company determines BESP for a product or service by considering multiple factors including, but not limited to, industry and market conditions, competitive landscape, standard pricing practices and internal cost models. Additionally, the Company considers historical transactions, including transactions whereby the deliverable was sold on a stand-alone basis. Deferred revenue primarily relates to support and maintenance and pertains to billings or payments received in advance where all of the revenue recognition criteria have not been met. The current portion of deferred revenue represents the amounts that are expected to be recognized as revenue within one year of the consolidated balance sheet date. Cost of Revenue Cost of revenue consists of product and fulfillment costs. Product costs include the cost of systems and disposable kits manufacture, related labor and personnel costs and allocated shared costs. Fulfillment costs consist of costs incurred in the shipping and handling of inventory including the shipping costs to the Company's customers, labor and related personnel costs related to receiving, inspecting, warehousing, and preparing systems and reusable kits for shipment. Cost of revenue for customer service is expensed as incurred and primarily consists of personnel costs such as salaries, bonuses and benefits and stock‑based compensation for employees associated with service contracts, travel costs and allocated shared costs (including rent and information technology). Research and Development Research and development costs are charged to operations as incurred. Warranty The Company provides a one-year warranty on the ARTAS System and accrues for the estimated future costs of repair or replacement upon customer acceptance or shipment. The warranty expense is accrued as a liability and recorded to cost of goods sold and is based upon historical information for the cost to repair or replace the system. Sales Taxes Revenue is recorded net of taxes collected from customers that are remitted to governmental authorities with the collected taxes recorded as current liabilities in accrued and other liabilities in the accompanying consolidated balance sheets until remitted to the relevant government authority. Income Taxes Income taxes are accounted for under the asset and liability method. Deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the tax and financial reporting bases of the Company’s assets and liabilities. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in future years in which those temporary differences are expected to be recovered or settled. Deferred tax assets are reduced through the establishment of a valuation allowance, if, based upon available evidence, it is determined that it is more likely than not that the deferred tax assets will not be realized. All deferred tax assets and liabilities are classified as non-current in the consolidated financial statements. Uncertain Tax Positions The Company recognizes the effect of income tax positions only if those positions are more likely than not of being sustained on examination based on the technical merit of the position. The first step is to evaluate the tax position for recognition by determining if the weight of available evidence indicates it is more likely than not that the position will be sustained on examination, including resolution of related appeals or litigation processes, if any. The second step is to measure the tax benefit as the largest amount, which is more than 50% likely of being realized upon ultimate settlement. The Company considers many factors when evaluating and estimating its tax positions and tax benefits, which may require periodic adjustments. The Company recognizes interest charges and penalties related to unrecognized tax benefits as a component of the tax provision. Stock-Based Compensation U.S. GAAP requires the measurement and recognition of compensation expense for all share-based payment awards, including stock options, using a fair-value based method. The Company estimates the fair value of share-based payment awards on the date of grant using a Black-Scholes-Merton option-pricing model. Stock-based compensation is recognized on a straight-line basis over the requisite service period based on awards ultimately expected to vest. Forfeitures are estimated at the time of grant and revised, if necessary, in subsequent periods if actual forfeitures differ from those estimates. Stock-based awards granted to non-employees are accounted for at fair value. The associated expense is recognized by the Company over the period the services are performed by non-employees. The fair value of stock-based awards granted to non-employees was nominal for the years ended December 31, 2017, 2016 and 2015. Net Loss Per Share Prior to the convervsion of all the preferred stock in connection with the IPO, the Company followed a two‑class method when computing net loss per common share as we issue shares that meet the definition of participating securities. The two‑class method determines net income (loss) per common share for each class of common stock and participating securities according to dividends declared or accumulated and participation rights in undistributed earnings. The two‑class method requires income for the period to be allocated between common stock and participating securities based upon their respective rights to receive dividends as if all income for the period had been distributed. Our convertible preferred stock contractually entitles the holders of such shares to participate in dividends, but does not contractually require the holders of such shares to participate in our losses. For periods in which the Company has reported net losses, diluted net loss per common share attributable to common stockholders is the same as basic net loss per common share attributable to common stockholders, because potentially dilutive common shares are not assumed to have been issued if their effect is anti‑dilutive. Defined Contribution Plan In 2006, the Company adopted a defined contribution retirement savings plan under Section 401(k) of the Internal Revenue Code (IRC). This plan covers employees who meet minimum age and service requirements and allows participants to defer a portion of their annual compensation on a pre-tax basis. Company contributions to the plan may be made at the discretion of the Board of Directors. There were no contributions by the Company during the years ended December 31, 2017, 2016 and 2015. 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 is (i) no longer an emerging growth company or (ii) affirmatively and irrevocably opt out of the extended transition period provided in the JOBS Act. As a result, these consolidated financial statements may not be comparable to companies that comply with the new or revised accounting pronouncements as of public company effective dates. Recently Issued Accounting Standards In May 2014, the FASB issued ASU No. 2014‑09, Revenue from Contracts with Customers The Company’s preliminary assessment of areas to be impacted by the new standard identified possible impact to the deferral of costs to obtain a contract, which are primarily commission expense directly incurred as a result of sales of products and related support, and the allocation of revenue between products and support and maintenance for certain arrangements. While the Company continues to assess the potential impact of the new standard, including the areas described above, it has not yet quantified the impact the new standard may have on its consolidated financial statements. In February 2016, the FASB issued ASU No. 2016‑02, Leases (Topic 842), or ASU 2016‑02, which requires lessees to record most leases on their balance sheets but recognize the expenses on their income statements in a manner similar to current practice. Under ASU 2016‑02, a lessee would recognize a lease liability for the obligation to make lease payments and a right‑to‑use asset for the right to use the underlying asset for the lease term. For public entities, this standard is effective for annual reporting periods beginning after December 15, 2018, including interim periods within that reporting period. For all other entities, this standard is 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 impact and materiality that this standard will have on its consolidated financial statements. However, the Company does expect an increase in its consolidated assets and liabilities upon adoption of this standard. Recently Adopted Accounting Standards In May 2017, the FASB issued ASU No. 2017-09 (Topic 718) Compensation—Stock Compensation: Scope of Modification Accounting, which provides guidance on the types of changes to the terms or conditions of share-based payment awards to which an entity would be required to apply modification accounting. The new standard is effective on a prospective basis for interim and annual periods beginning after December 15, 2017, with early adoption permitted. The Company early adopted this ASU on a prospective basis in the fourth quarter of fiscal 2017. Prior periods were not retrospectively adjusted. The adoption of the ASU did not have a material impact on the consolidated financial statements. In November 2016, the FASB issued ASU No. 2016-18 (Topic 230) Statement of Cash Flow: Restricted Cash, which provides guidance on the classification of restricted cash to be included with cash and cash equivalents when reconciling the beginning of period and end of period total amounts on the statement of cash flows. The amendments of this ASU are effective for interim and annual periods beginning after December 15, 2017, with early adoption permitted. The standard must be applied retrospectively to all periods presented. The Company has early adopted this standard in the fourth quarter of fiscal 2017 and the adoption did not have a material impact on its consolidated financial statements. In August 2016, the FASB issued ASU No. 2016‑15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments, or ASU 2016‑15. ASU 2016-15 identifies how certain cash receipts and cash payments are presented and classified in the Statement of Cash Flows. For public entities, this standard is effective for annual reporting periods beginning after December 15, 2017, including interim periods within that reporting period. For all other entities, this standard is effective for annual reporting periods beginning after December 15, 2018, and interim periods within annual periods beginning after December 15, 2019. This standard should be applied retrospectively and early adoption is permitted, including adoption in an interim period. The Company has early adopted this standard in the fourth quarter of fiscal 2017 and the adoption did not have a material impact on its consolidated financial statements. In March 2016, the FASB issued ASU No. 2016‑09, Compensation – Stock Compensation (Topic 718): Improvements to Employee Share‑Based Payment Accounting, or ASU 2016‑09. ASU 2016-09 simplifies the accounting and reporting of share‑based payment transactions, including adjustments to how excess tax benefits and payments for tax withholdings should be classified and provides the election to eliminate the estimate for forfeitures. For public entities, this standard is effective for annual reporting periods beginning after December 15, 2016, including interim periods within that reporting period. For all other entities, this standard is effective for annual reporting periods beginning after December 15, 2017, and interim periods within annual periods beginning after December 15, 2018. Early adoption is permitted for any entity in any interim or annual period for which financial statements have not been issued or made available for issuance. The Company early adopted this ASU on a prospective basis in the fourth quarter of fiscal 2017. Prior periods were not retrospectively adjusted. The adoption of the ASU did not have a material impact on the consolidated financial statements. In July 2015, the FASB issued ASU No. 2015-11, Inventory, Simplifying the Measurement of Inventory (Topic 330), or ASU 2015-11. Under ASU 2015-11, the measurement principle for inventory will change from lower of cost or market value to lower of cost and net realizable value. Net realizable value is the estimated selling price in the ordinary course of business, less reasonably predictable costs of completion, disposal and transportation. For public entities, this standard is effective for annual reporting periods beginning after December 15, 2016, including interim periods within that reporting period. For all other entities, this standard is effective for annual reporting periods beginning after December 15, 2016, and interim periods within annual periods beginning after December 15, 2017. This standard should be applied prospectively and early adoption is permitted. The Company adopted this ASU on a prospective basis in the fourth quarter of fiscal 2017. Prior periods were not retrospectively adjusted. The adoption of the ASU did not have a material impact on the consolidated financial statements.

Net Loss per Share

Net Loss per Share	12 Months Ended
	Dec. 31, 2017
Earnings Per Share [Abstract]
Net Loss per Share	3. NET LOSS PER SHARE Net Loss Per Share Basic net loss per share is calculated by dividing net loss by the weighted-average number of common shares outstanding during the period, without consideration for common stock equivalents. Diluted net loss per share is computed by dividing net loss by the weighted-average number of common share equivalents outstanding for the period determined using the treasury-stock method. For purposes of this calculation, convertible preferred stock, preferred stock warrants and stock options are considered to be common stock equivalents and are only included in the calculation of diluted net loss per share when their effect is dilutive. Due to the net loss, all the outstanding shares of common stock equivalents were excluded from the calculation of diluted net loss per share attributable to common stockholders for the periods presented because including them would have been antidilutive: As of December 31, 2017 2016 2015 Options to purchase common stock 1,930,752 1,831,757 1,410,708 Convertible preferred stock — 21,142,295 19,336,777 Warrants for preferred stock — 385,126 385,126 Warrants for common stock 306,456 — — Total potential dilutive shares 2,237,208 23,359,178 21,132,611

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Fair Value Measurements	4. FAIR VALUE MEASUREMENTS Cash and cash equivalents, restricted cash, accounts receivable, accounts payable, and accrued liabilities approximate fair market value because of the short-term nature of those instruments. Management believes that the long-term note bearing variable interest represents the prevailing market rates for instruments with similar characteristics; accordingly, the carrying value of this instrument approximates its fair value. U.S. GAAP established a framework for measuring fair value and a fair value hierarchy based on the inputs used to measure fair value. This framework maximizes the use of observable inputs and minimizes the use of unobservable inputs by requiring that the observable inputs be used when available. Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. It applies to both items recognized and reported at fair value in the consolidated financial statements and items disclosed at fair value in the notes to the consolidated financial statements. Observable inputs are inputs that market participants would use in pricing the asset or liability based on market data obtained from independent sources. Unobservable inputs reflect assumptions that market participants would use in pricing the asset or liability based on the best information available in the circumstances. The hierarchy is broken down into three levels based on the transparency of inputs as follows: Level - Quoted prices are available in active markets for identical assets or liabilities as of the report date. A quoted price for an identical asset or liability in an active market provides the most reliable fair value measurement because it is directly observable to the market. Level - Pricing inputs are other than quoted prices in active markets, which are either directly or indirectly observable as of the report date. The nature of these securities include investments for which quoted prices are available but traded less frequently and investments that are fair valued using other securities, the parameters of which can be directly observed. Level - Securities that have little to no pricing observability as of the report date. These securities are measured using management’s best estimate of fair value, where the inputs into the determination of fair value are not observable and require significant management judgment or estimation. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement. However, the determination of what constitutes “observable” requires significant judgment by the Company. The categorization of a financial instrument within the hierarchy is based upon the pricing transparency of the instrument and does not necessarily correspond to the Company’s perceived risk of that instrument. The following tables summarize the levels of fair value measurements of the Company’s cash equivalents, investments and preferred stock warrants liabilities: Fair Value Measurements as of December 31, 2017 Quoted Prices in Active Markets using Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total Assets Cash Equivalents: Money market accounts $ 23,545 $ — $ — $ 23,545 Restricted cash 100 — — 100 Total assets $ 23,645 $ — $ — $ 23,645 Fair Value Measurements as of December 31, 2016 Quoted Prices in Active Markets using Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total Assets Cash Equivalents: Money market accounts $ 11,906 $ — $ — $ 11,906 Restricted cash 100 — — 100 Total assets $ 12,006 $ — $ — $ 12,006 Liabilities Preferred stock warrant liabilities $ — $ — $ 693 $ 693 The following table summarizes the preferred stock warrant liabilities activity subject to Level 3 inputs which are measured on a recurring basis until their exercises: Fair value measurements of warrants using significant unobservable inputs (Level 3) Balance as of January 1, 2015 $ 659 Change in fair value of preferred stock warrants (578 ) Fair value of preferred stock warrants issued 266 Balance as of December 31, 2015 347 Change in fair value of preferred stock warrants 346 Balance as of December 31, 2016 693 Change in fair value of preferred stock warrants 387 Fair value of preferred stock warrants converted to common stock warrants (1,080 ) Balance as of December 31, 2017 $ —

Balance Sheet Components

Balance Sheet Components	12 Months Ended
	Dec. 31, 2017
Balance Sheet Components [Abstract]
Balance Sheet Components	5. BALANCE SHEET COMPONENTS Inventory Inventory December 31, 2017 2016 Finished goods $ 2,761 $ 2,580 Raw materials — 162 Total inventory $ 2,761 $ 2,742 Property and Equipment, Net Property December 31, 2017 2016 Computer hardware and software $ 721 $ 647 Equipment 2,929 2,818 Leasehold improvements 869 1,094 Furniture and fixtures 270 82 Total property and equipment 4,789 4,641 Less: Accumulated depreciation and amortization (3,651 ) (3,182 ) Total property and equipment, net $ 1,138 $ 1,459 Depreciation and amortization expense was $574, $654, $860 for the years ended December 31, 2017, 2016 and 2015. Accrued and Other Liabilities Accrued December 31, 2017 2016 Payroll and related expense $ 1,630 $ 1,647 Other* 1,125 791 Total accrued and other liabilities $ 2,755 $ 2,438 * Other consists of items that are individually less than 5% of total current liabilities.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2017
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	6. COMMITMENTS AND CONTINGENCIES Operating Leases The Company has various operating leases including 23,000 square feet of office space in San Jose, California, which expires in April 2022. The Company recognizes rent expense on a straight-line basis over the non-cancelable lease period and records the difference between cash rent payments and the recognition of rent expense as a deferred rent liability. When leases contain escalation clauses, rent abatements and/or concessions, such as rent holidays and landlord or tenant incentives or allowances, the Company applies them in the determination of straight-line rent expense over the lease period. Aggregate future minimum lease payments required under the Company’s operating leases as of December 31, 2017 are as follows: Years ending December 31, 2018 $ 503 2019 518 2020 534 2021 550 Thereafter 188 Total future minimum lease payments $ 2,293 The total rent expense for all operating leases for the years ended December 31, 2017, 2016 and 2015 was $413, $315, and $322. Licensing Agreements In July 2006, the Company entered into a license agreement with Rassman Licensing, LLC (Rassman) for non-exclusive, royalty bearing, non-transferable, perpetual, world-wide rights for use on approved fields relating to robotically controlled hair removal and implantation procedures. In consideration for this license, the Company paid Rassman a one-time payment of $1,000. The agreement terminates on May 9, 2020. In February 2012, the Company amended its license agreement with Rassman. In exchange for a one-time $400 payment to Rassman, the Company now has a fully paid royalty-free license to a patent subject to this license agreement. Royalties for the years ended December 31, 2017, 2016 and 2015 were $0. In July 2006, the Company entered into a license agreement with HSC Development, LLC for exclusive non-transferable, royalty-free worldwide rights for use in approved fields relating to a computer-controlled system in which a device is carried on a mechanized arm for extraction or implantation of a follicular unit without manual manipulation. In consideration for this license, the Company paid HSC Development, LLC a one-time payment of $25 and issued 2,500 shares of the Company’s common stock valued. The agreement terminates on July 27, 2024.

Long-Term Debt

Long-Term Debt	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Long-Term Debt	7. LONG-TERM DEBT Loan and Security Agreement In May 2015, the Company entered into a loan and security agreement with Oxford Finance, LLC, or Oxford, (the Agreement). Under the terms of the loan and security agreement, the Company borrowed $20,000 with an interest rate at prime plus 8.5% per annum, which is collateralized by all personal property of the Company excluding intellectual property, and issued 10-year warrants to purchase 110,486 shares of Series C Preferred Stock at $7.15 per share. The estimated fair value of the warrants at issuance was recorded as a discount on the loan and amortized into interest expense over the expected life of the loan. In connection with the loan agreement, the Company recorded $246 of credit facility fees and $153 of debt issuance cost as of January 31, 2015. The credit facility fees and debt issuance costs are a discount on the debt and are being amortized to interest expense over the term of the loan using the effective-interest method. The loan will mature in July 2019, at which time the Company must repay the outstanding principal balance which includes a final payment of $1,300. The outstanding principal balance on the loan was $13,300 and accrued interest totaled $85 as of December 31, 2017. The interest rate was 13% at December 31, 2017. Borrowings under the Agreement are collateralized by all the assets of the Company excluding intellectual property. The Agreement includes customary restrictive covenants that impose operating and financial restrictions on the Company, including restrictions on our ability to take actions that could be in the Company’s best interests. These restrictive covenants include operating covenants restricting, among other things, the Company’s ability to incur additional indebtedness, effect certain acquisitions or make other fundamental changes. The Company was in compliance with all of the covenants as of December 31, 2017 and 2016. The scheduled principal payments on the outstanding borrowings as of December 31, 2017 are as follows: As of December 31, 2017 2018 $ 8,000 2019 5,300 Total 13,300 Less debt discount (299 ) Less current portion (7,730 ) Non-current portion $ 5,271 For the year ended December 31, 2017 and 2016, the Company made principal repayments of $8,000 and $0. Convertible Notes On September 6, 2017, the Company issued $5,000 in subordinated convertible notes (Convertible Notes) that accrued interest at 5.0% per annum, in a private placement transaction with certain of the Company’s existing stockholders and their affiliated entities, including investors affiliated with certain of the Company’s directors. Pursuant to the terms of the Convertible Notes, the aggregate outstanding principal and unpaid but accrued interest automatically converted into 718,184 shares of the Company’s common stock, upon the consummation of the IPO. There was no outstanding balance on the Convertible Notes as of December 31, 2017.

Preferred Stock

Preferred Stock	12 Months Ended
	Dec. 31, 2017
Temporary Equity Disclosure [Abstract]
Preferred Stock	8. PREFERRED STOCK As of December 31, 2017, the Company had 10,000,000 shares of preferred stock authorized with a par value of $0.0001. No shares of preferred stock were outstanding as of December 31, 2017. Convertible Preferred Stock During the year ended December 31, 2017, the Company issued an aggregate of 1,529,306 shares of Series C convertible preferred stock for net cash proceeds of $10,209, net of issuance cost of $726. Upon the closing of the IPO (as discussed in Note 1), all outstanding shares of Series A, Series AA, Series B and Series C convertible preferred stock converted into 22,671,601 shares of common stock. During the year ended December 31, 2016, the Company issued an aggregate of 1,805,518 shares of Series C convertible preferred stock for net cash proceeds of $12,073, net of issuance cost of $837. The convertible preferred stock as of December 31, 2016 consisted of the following: December 31, 2016 Convertible Preferred Stock: Shares Authorized Shares Outstanding Net Carrying Value Liquidation Preference Series A 25,092,906 2,509,232 $ 11,140 $ 11,292 Series B 38,461,538 3,846,132 24,926 25,000 Series C 170,100,000 14,536,931 97,693 103,939 Series AA 2,500,000 250,000 1,976 2,000 Total convertible preferred stock 236,154,444 21,142,295 $ 135,735 $ 142,231 On issuance, the Company’s convertible preferred stock was recorded at fair value or the amount of allocated proceeds, net of issuance costs. The Company’s convertible preferred stock was classified outside of stockholders’ equity (deficit) from issuance through the closing of the IPO, because, in the event of certain “liquidation events” that are not solely within the Company’s control (including merger, acquisition, or sale of all or substantially all of the Company’s assets), the shares would have become redeemable at the option of the holders. The Company did not adjust the carrying values of the convertible preferred stock to the deemed liquidation values of such shares since a liquidation event was not probable at any of the reporting dates.

Preferred and Common Stock Warr

Preferred and Common Stock Warrants	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Preferred and Common Stock Warrants	9. PREFERRED AND COMMON STOCK WARRANTS As of December 31, 2016, the preferred stock warrants consisted of the following: Warrants Outstanding December 31, 2016 Exercise Price Expiration Series C preferred stock warrants 274,640 $ 7.15 Various dates in 2023 - 2024 Series C preferred stock warrants 110,486 7.15 May 19, 2025 Total preferred stock warrants 385,126 There was no change in the total preferred stock warrants balance from January 1, 2017 to immediately prior to the closing of the IPO. On the closing of the IPO, all outstanding convertible preferred stock warrants automatically converted into common stock warrants. As such, the Company reclassified the outstanding preferred stock warrant liability to additional paid in capital in stockholder’s equity (deficit). During the year ended, December 31, 2017, a total of 78,670 of common stock warrants were net exercised for 15,112 shares of common stock. As of December 31, 2017, there were 306,456 common stock warrants outstanding exercisable into the same number of shares of common stock at an exercise price of $7.15 with expiration dates ranging from 2018 to 2025. From January 1, 2017 through September 30, 2017, the Company estimated the fair value of each preferred stock warrant using a probability weighed expected return method (PWERM) that uses an option pricing method (OPM), together with a Monte Carlo simulation to incorporate the anti-dilution provisions on the convertible preferred stock, to allocate the estimated value of the Company. The OPM treated classes of stock as call options on a company's enterprise value which took into consideration differences in the right of various securities including rights to dividends, liquidation preferences, and conversion rights. The OPM priced the call option using the Black-Scholes model. The PWERM relied on a forward-looking analysis to predict the possible future value of a company by weighing discrete future outcomes. The fair value of preferred stock warrants was determined using the following assumptions: Year Ended December 31 2016 Expected term (years) 2.00 Risk-free interest rate 1.20 % Expected volatility 70.90 % The estimated expected volatility was derived from historical volatilities of several unrelated publicly listed peer companies over a period approximately equal to the remaining term of the warrants. When making the selections of the Company’s industry peer companies to be used in the volatility calculation, the Company considered the size and operational and economic similarities to the Company’s principle business operations. The estimated expected term represented either the lesser of (i) the remaining contractual term of the warrants or (ii) the remaining term under probable scenarios used to determine the fair value of the underlying stock. The risk-free interest rate was based on the U.S. Treasury yield for a term consistent with the estimated expected term. The significant unobservable inputs used in the fair value measurement of the convertible preferred stock warrant liability were the fair value of the underlying stock at the valuation date, the expected volatility, and the estimated term of the warrants. On the closing of the IPO, the Company remeasured the preferred stock warrant liability to fair value of $1,080 before the warrant liability converted into additional paid-in-capital. The Company estimated the fair value of the preferred stock warrant liability using the Black-Scholes-Merton Expected term (years) 1.00-7.61 Risk-free interest rate 1.31-2.16% Expected volatility 72%

Common Stock Reserved For Issua

Common Stock Reserved For Issuance	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Common Stock Reserved For Issuance	10. COMMON STOCK RESERVED FOR ISSUANCE The Company is 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 of all outstanding shares of convertible preferred stock (and preferred stock warrants), plus options granted and available for grant under the incentive plans. December 31, 2017 December 31, 2016 Conversion of outstanding Series A convertible preferred stock — 2,509,232 Conversion of outstanding Series B convertible preferred stock — 3,846,132 Conversion of outstanding Series C convertible preferred stock — 14,536,931 Conversion of outstanding Series AA convertible preferred stock — 250,000 Outstanding preferred stock warrants — 385,126 Outstanding common stock warrants 306,456 — Outstanding and issued stock options 1,930,752 1,831,757 Shares reserved for future option grants 271,490 392,306 Total common stock reserved for issuance 2,508,698 23,751,484

Stock Option Plan

Stock Option Plan	12 Months Ended
	Dec. 31, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock Option Plan	11. STOCK OPTION PLAN 2017 Plan The 2017 Equity Incentive Plan (2017 Plan) became effective on October 11, 2017. Under the 2017 Plan, 1,913,831 shares of common stock were initially reserved for the grant of incentive stock options (ISOs), nonstatutory stock options (NSOs), stock appreciation rights, restricted stock awards, restricted stock unit awards, and other forms of equity compensation to employees, directors and consultants. In addition, the Company’s 2017 Plan provides for the grant of performance cash awards to employees, directors and consultants. Prior to the 2017 Plan, 306,756 shares that had been available for future awards under 2015 Plan (defined below) as of October 11, 2017, were added to the initial reserve available under 2017 Plan, bringing the total number of shares reserved for issuance under the 2017 Plan upon effective date to 2,220,587 shares. The number of shares reserved for issuance under the 2017 Plan will increase automatically on the first day of each fiscal year beginning in 2018 and ending in 2027, equal to the lesser of (i) 4% of the shares of stock outstanding on the last day of the immediately preceding fiscal year or (ii) number of shares of stock as determined by the Company’s board of directors. 2005 and 2015 Plan The Company granted options under 2015 Equity Incentive Plan (the 2015 Plan) and 2005 Stock Option Plan (the 2005 Plan) until October 2017 when they were terminated as to future awards, although they continue to govern the terms of options that remain outstanding under the 2005 Plan and the 2015 Plan, as the case may be. The 2005 Plan provided for the granting of ISOs and NSOs. In 2015, the Company established its 2015 Plan, which superseded and replaced the 2005 Plan. In connection with the Board of Directors approval of the 2017 Plan, all remaining shares available for future award under the 2015 Plan were transferred to the 2017 Plan, and the 2015 Plan was terminated. The Company recognized stock-based compensation for its employees and non-employees in the accompanying consolidated statements of operations as follows: Year Ended December 31, 2017 2016 2015 Cost of revenue $ 10 $ 12 $ 12 Research and development 101 102 116 Sales and marketing 74 85 140 General and administrative 280 267 161 Total stock-based compensation $ 465 $ 466 $ 429 Determination The estimated Year Ended December 31, 2017 2016 2015 Expected term (in years) 4.95-7.50 5.53–6.11 5.00 – 6.07 Risk-free interest rate 1.77-2.13% 1.30–1.84% 1.47– 1.82% Expected volatility 51.62-55.38% 52.71–56.58% 51.93-58.21% Expected dividend rate 0% 0% 0% The fair value of each stock option grant was determined by the Company using the methods and assumptions discussed below. Each of these inputs is subjective and generally requires significant judgment and estimation by management. Expected Term —The expected term represents the period that stock-based awards are expected to be outstanding. The expected term for option grants is determined using the simplified method. The simplified method deems the term to be the average of the time-to-vesting and the contractual life of the stock-based awards. The expected term for options issued to non-employees is the contractual term. Expected Volatility —Since the Company does not have a trading history for its common stock, the expected volatility was derived from the historical stock volatilities of comparable peer public companies within its industry that are considered to be comparable to the Company’s business over a period equivalent to the expected term of the stock-based awards. Risk-Free Interest Rate —The risk-free interest rate is based on the U.S. Treasury yield curve in effect at the date of grant for zero-coupon U.S. Treasury notes with maturities approximately equal to the stock-based awards’ expected term. Expected Dividend Rate —The expected dividend is zero as the Company has not paid nor does it anticipate paying any dividends on its common stock in the foreseeable future. Forfeiture Rate —The forfeiture rate is estimated based on an analysis of actual forfeitures. Management will continue to evaluate the adequacy of the forfeiture rate based on actual forfeiture experience, analysis of employee turnover behavior and other factors. The impact from any forfeiture rate adjustment would be recognized in full in the period of adjustment and if the actual number of future forfeitures differs from management’s estimates, the Company might be required to record adjustments to stock-based compensation in future periods. Fair Value of Common Stock —Prior to the closing of the Company’s IPO, the fair value of the Company’s common stock was determined by the Company’s board of directors because there was no public market for the Company’s common stock as the Company was a private company. The Company’s board of directors determined the fair value of the common stock by considering a number of objective and subjective factors, including having valuations of its common stock performed by an unrelated valuation specialist, valuations of comparable peer public companies, sales of the Company’s convertible preferred stock to unrelated third parties, operating and financial performance, the lack of liquidity of the Company’s capital stock, and general and industry-specific economic outlook. After the closing of the Company’s IPO, the fair value of the Company’s common stock is used to estimate the fair value of the stock-based awards at grant date. The following table summarizes stock option activity under the Company’s stock option plan: Number of Shares Weighted- Average Exercise Price per Share Weighted- Average Remaining Contractual Term Aggregate Intrinsic Value Outstanding – January 1, 2015 1,258,429 $ 1.80 Options granted 532,930 1.80 Options exercised (79,893 ) 1.40 Options cancelled (294,654 ) 1.40 Options expired (6,104 ) 2.30 Outstanding – December 31, 2015 1,410,708 1.90 7.9 $ — Options granted 1,179,644 1.70 Options exercised (20,218 ) 2.00 Options cancelled (737,377 ) 2.00 Options expired (1,000 ) 0.50 Outstanding – December 31, 2016 1,831,757 1.80 8.7 $ 14 Options granted 192,420 3.12 Options exercised (21,843 ) 2.01 Options cancelled (71,582 ) 1.81 Outstanding – December 31, 2017 1,930,752 $ 1.90 7.9 $ 5,322 Vested and expected to vest – December 31, 2017 1,667,332 $ 1.90 7.8 $ 4,590 Exercisable – December 31, 2017 960,933 $ 1.80 7.2 $ 3,257 The weighted-average grant date fair value of options granted was $1.73, $0.86 and $1.10 per share for years ended December 31, 2017, 2016 and 2015. The total intrinsic value of options exercised were $1.18, $0 and $47 for years ended December 31, 2017, 2016 and 2015. Unamortized stock-based compensation was $722 as of December 31, 2017, which is expected to be recognized over a weighted-average period of approximately 2.63 years.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income Taxes	12. INCOME TAXES The geographical breakdown of loss before provision for income taxes is as follows: Year Ended December 31, 2017 2016 2015 Domestic $ (17,732 ) $ (21,696 ) $ (22,535 ) Foreign (54 ) (150 ) (436 ) Net loss before provision for income taxes $ (17,786 ) $ (21,846 ) $ (22,971 ) The components of the provision for income taxes are as follows: Year Ended December 31, 2017 2016 2015 Current tax provision: Federal $ — $ — $ — State 4 4 4 Foreign 56 16 17 Total current tax provision 60 20 21 Deferred tax provision (benefit): State (4 ) (4 ) (4 ) Foreign — (16 ) (17 ) Total deferred tax provision (benefit) $ (4 ) $ (20 ) $ (21 ) Total provision for income taxes $ 56 $ — $ — Deferred income taxes reflect the net tax effects of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes. A valuation allowance is provided when it is more likely than not that the deferred tax assets will not be realized. The Company has established a valuation allowance to offset net deferred tax assets for all periods presented due to the uncertainty of realizing future tax benefits from net operating loss carryforwards and other deferred tax assets. The valuation allowance decreased by $13,888 and increased by $7,634 for the years ended December 31, 2017 and 2016. The decrease in valuation allowance in 2017 was due to the change in the corporate tax rate from 35% to 21% and the resulting revaluation of the deferred tax assets. On December 22, 2017, the Tax Cuts and Jobs Act (the "Act") was enacted into law making significant changes to the Internal Revenue Code. Changes include, but are not limited to, a federal corporate tax rate decrease from 35% to 21% for tax years beginning after December 31, 2017, the transition of U.S. international taxation from a worldwide tax system to a territorial system and a one-time transition tax on the mandatory deemed repatriation of foreign earnings. ASC 740 requires the Company to recognize the effect of the tax law changes in the period of enactment. However, the SEC staff has issued SAB 118 which will allow the Company to record provisional amounts during a measurement period. The Company has concluded that a reasonable estimate could be developed for the effects of the tax reform. However, due to the short time frame between the enactment of the reform and the year end, its fundamental changes, the accounting complexity, and the expected ongoing guidance and accounting interpretations over the next 12 months, the Company considers the accounting of the deferred tax remeasurement and other items to be reasonable estimates. These effects have been included in the consolidated financial statements for the year ended December 31, 2017 as provisional amounts, which had no effect on the benefit from taxes on income due to the valuation allowance. During the measurement period, the Company might need to reflect adjustments to the provisional amounts upon obtaining, preparing, or analyzing additional information about facts and circumstances that existed as of the enactment date that, if known, would have affected the income tax effects initially reported as provisional amounts. The measurement period will end when the Company obtains, prepares, and analyzes the information needed in order to complete the accounting requirements under ASC Topic 740 or on December 22, 2018, whichever is earlier. The Company expects to complete its analysis within the measurement period in accordance with SAB 118. Our effective tax rate substantially differed from the federal statutory tax rate of 34% primarily due to the change in the valuation allowance for our deferred tax assets. The reconciliation between income taxes computed at the federal statutory income tax rate and the provision for income taxes is as follows: Year Ended December 31, 2017 2016 2015 U.S. federal statutory income tax at 34% $ (6,046 ) $ (7,306 ) $ (7,973 ) Research tax credits (75 ) (99 ) (82 ) Stock-based compensation 85 102 125 Adjustment of deferred tax balances following changes in tax rates 20,748 — — Other 303 117 599 Change in valuation allowance (14,955 ) 7,206 7,352 Total current tax provision 60 20 21 Total deferred tax benefit (4 ) (20 ) (21 ) Total provision for income taxes $ 56 $ — $ — The components of the deferred tax assets are as follows: December 31, 2017 2016 Deferred tax assets: Net operating loss carryforwards $ 37,173 $ 51,104 Research and development credits 2,823 2,456 Accrual and reserves 1,251 1,575 Total deferred tax assets 41,247 55,135 Less: valuation allowance (41,247 ) (55,135 ) Total net deferred tax assets $ — $ — As of December 31, 2017, the Company has federal and state net operating loss (“NOL) carryforwards of approximately $154,250 and $96,696. The use of these NOL carryforwards might be subject to limitation under the rules regarding a change in stock ownership as determined by the IRC and similar state provisions (the “Code”); however, a complete analysis of the limitation of the NOL carryforwards will not be complete until the time the Company projects it will be able to utilize such NOLs. The NOL carryforwards expire between 2018 and 2037, and valuation allowances have been reserved, where necessary. In addition, as of December 31, 2017, the Company also had NOL carryforwards in South Korea of approximately $1,102 which begin to expire in 2025. The Company also had federal and state research and development credit carryforwards of approximately $1,490 and $1,687, as of December 31, 2017. The federal credit will expire starting in 2025 if not utilized. The state credits have no expiration date. Utilization of the research and development credit carryforwards may be subject to an annual limitation due to the ownership percentage change limitations provided by the Code. However, the Company has not conducted a formal study to determine the extent of the limitations, which could impact the realizability of these credit carryforwards in future periods. The annual limitations may result in the expiration of the net operating losses and research and development credits before utilization. The Company has not provided for U.S. income taxes on undistributed earnings of its foreign subsidiaries because it intends to permanently re-invest these earnings outside the U.S. The cumulative amount of such undistributed earnings upon which no U.S. income taxes have been provided was $122 as of December 31, 2017. It is not practicable to determine the income tax liability that might be incurred if these earnings were to be repatriated to the U.S. Uncertain Tax Positions The activity related to the gross amount of unrecognized tax benefits is as follows: Year Ended December 31, 2017 2016 Balance as of the beginning of the year $ 1,283 $ 1,186 Increases related to tax positions in prior period 5 16 Increases related to tax positions taken during the current period 74 81 Balance at the end of the year $ 1,362 $ 1,283 These amounts are related to certain deferred tax assets with a corresponding valuation allowance. If recognized, the impact on the Company’s effective tax rate would not be material due to the full valuation allowance. Management believes that there will not be any significant changes in our unrecognized tax benefits in the next 12 months. The Company recognizes interest and penalties related to unrecognized tax benefits in the provision for income taxes in the accompanying consolidated statement of operations. Accrued interest and penalties, if applicable, are included in accrued liabilities in the consolidated balance sheet. For the years ended December 31, 2017, 2016 and 2015, the Company did not recognize any accrued interest and penalties. The Company files income tax returns in the United States and in various state jurisdictions with varying statutes of limitations. Tax years 2002 through 2017 remain open to examination by the United States and various state jurisdictions. The Company is not currently under examination by the Internal Revenue Service or any other jurisdiction for any year.

Geographic Information

Geographic Information	12 Months Ended
	Dec. 31, 2017
Segment Reporting [Abstract]
Geographic Information	13. GEOGRAPHIC INFORMATION The following Year Ended December 31, 2017 2016 2015 United States $ 8,919 $ 6,736 $ 8,252 Europe and Middle East 5,784 3,112 2,940 Asia Pacific 4,353 3,552 2,989 Rest of World 2,241 2,200 3,049 Total revenue $ 21,297 $ 15,600 $ 17,230 As of December 31, 2017 and 2016, all long-term assets were located within the United States.

Selected Quarterly Financial Da

Selected Quarterly Financial Data	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Data [Abstract]
Selected Quarterly Financial Data	14. SELECTED QUARTERLY FINANCIAL DATA The following tables present certain selected unaudited consolidated quarterly financial information for each of the eight quarters ended December 31, 2017. This consolidated quarterly information has been prepared on the same basis as the consolidated financial statements and includes all adjustments necessary to state fairly the information for the periods presented. The selected consolidated quarterly financial results from operations for the years ended December 31, 2017 and 2016 are set forth therein. Net loss per share for all periods presented has been retroactively adjusted to reflect the 1-for-10 reverse stock split effected on September 15, 2017. Fiscal 2017 Quarter Ended, March 31, 2017 Unaudited June 30, 2017 Unaudited September 30, 2017 Unaudited December 31, 2017 Unaudited Revenue, net $ 5,475 $ 5,789 $ 4,177 $ 5,856 Gross profit $ 2,383 $ 2,302 $ 1,703 $ 2,759 Net loss $ (5,175 ) $ (5,007 ) $ (6,596 ) $ (1,064 ) Basic and diluted net loss per share $ (3.20 ) $ (3.09 ) $ (4.07 ) $ (0.04 ) Fiscal 2016 Quarter Ended, March 31, 2016 Unaudited June 30, 2016 Unaudited September 30, 2016 Unaudited December 31, 2016 Unaudited Revenue, net $ 3,187 $ 3,559 $ 3,676 $ 5,178 Gross profit $ 779 $ 1,104 $ 1,272 $ 2,014 Net loss $ (5,814 ) $ (5,172 ) $ (5,928 ) $ (4,932 ) Basic and diluted net loss per share $ (3.61 ) $ (3.21 ) $ (3.67 ) $ (3.06 )

Related Party Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2017
Related Party Transactions [Abstract]
Related Party Transactions	15. RELATED PARTY TRANSACTIONS During the years ended December 31, 2017 and 2016, the Company has engaged in a commercial transaction with a then-member of the Company’s board of directors. The aggregate revenue for this transaction was $83 and $240 for the years ended December 31, 2017 and 2016. There were no accounts receivable due from this then-member of the board of directors as of December 31, 2017 and 2016. In January 2017, that member of the Company’s board of directors resigned.

Summary of Significant Accoun24

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Liquidity	Liquidity These consolidated financial statements are prepared on a going concern basis that contemplates the realization of assets and extinguishment of liabilities in the normal course of business. The Company has incurred net operating losses and negative cash flows from operations since inception. As of December 31, 2017 and 2016, the Company has an accumulated deficit of $164,487 and $146,645 and, as of such dates, did not have sufficient capital to fund its planned operations. As a result of the Company’s recurring losses from operations and negative cash flows, the Company’s independent registered public accounting firm included an explanatory paragraph in its current report on the Company’s consolidated financial statements that such factors raise substantial doubt about the Company’s ability to continue as a going concern. Management plans to manage expenses and obtain additional funds through a combination of equity and debt financing. The Company will need to raise further capital in the future to service its debt or fund its operations until the time it can sustain positive cash flows. There can be no assurance that the Company will be successful in raising additional capital or that such capital, if available, will be on terms that are acceptable to the Company. If the Company is unable to raise sufficient additional capital, it may be compelled to reduce the scope of its operations and planned capital expenditures or sell certain assets, including intellectual property assets. The accompanying consolidated financial statements have been prepared on a going concern basis, which contemplates the realization of assets and the satisfaction of liabilities in the normal course of business, and, as such, the consolidated financial statements do not include any adjustments relating to the recoverability and classification of recorded asset amounts or amounts and classification of liabilities that might be necessary should the Company be unable to continue in existence.
Basis of Presentation	Basis of Presentation The accompanying consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United States of America (U.S. GAAP). The accompanying consolidated financial statements include the accounts of Restoration Robotics, Inc. and its wholly owned subsidiaries.
Principles of Consolidation	Principles of Consolidation The accompanying consolidated financial statements include the accounts of Restoration Robotics, Inc. and its wholly owned subsidiaries, which are located in the United States, United Kingdom, Spain, Hong Kong and South Korea. All significant intercompany accounts and transactions have been eliminated in consolidation.
Use of Estimates	Use of Estimates The preparation of the consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the date of the consolidated financial statements and the reported amounts of revenue and expenses during the reporting period. Significant estimates and assumptions made in the accompanying consolidated financial statements include, but are not limited to revenue recognition, the fair value of common stock, the fair value of preferred stock warrant liabilities, and the recoverability of the Company’s net deferred tax assets, and related valuation allowance. The Company evaluates its estimates and assumptions on an ongoing basis using historical experience and other factors and adjusts those estimates and assumptions when facts and circumstances dictate. Actual results could materially differ from those estimates.
Segments	Segments Operating segments are defined as components of an entity for which separate financial information is available and that is regularly reviewed by the Chief Operating Decision Maker (CODM) in deciding how to allocate resources to an individual segment and in assessing performance. The Company's CODM is its Chief Executive Officer. The Company has determined it operates in a single operating segment and has one reportable segment, as the CODM reviews financial information presented on a consolidated basis for purposes of making operating decisions, allocating resources, and evaluating financial performance.
Foreign Currency	Foreign Currency The functional currency of the Company’s non-U.S. subsidiaries is the local currency. Asset and liability balances denominated in non-U.S. dollar currencies are translated into U.S. dollars using period-end exchange rates, while revenue and expenses are based upon the exchange rate at the time of the transaction, if known, or at the average rate for the period. Differences are included in stockholders’ equity (deficit) as a component of accumulated other comprehensive loss. Financial assets and liabilities denominated in currencies other than the functional currency are recorded at the exchange rate at the time of the transaction and subsequent gains and losses related to changes in the foreign currency are included in other income (expense), net in the accompanying consolidated statements of operations. The net foreign transaction gain or losses were insignificant for all periods presented.
Cash and Cash Equivalents	Cash and Cash Equivalents The Company considers all highly liquid investments with an original maturity of three months or less from the date of purchase to be cash equivalents. Cash and cash equivalents consists primarily of funds invested in readily available checking and savings accounts, investments in money market funds and short-term time deposits. The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the balance sheets that sum to the total of the same amounts shown in the statements of cash flows. December 31, 2017 2016 Cash and cash equivalents $ 23,545 $ 11,906 Restricted cash 100 100 Total cash, cash equivalents and restricted cash in the consolidated statements of cash flows $ 23,645 $ 12,006
Restricted Cash	Restricted Cash As of December 31, 2017 and 2016, the Company was required to hold $100 in a separate money market account as collateral for credit cards. These amounts are recorded in other assets in the accompanying consolidated balance sheets.
Concentration of Credit Risk	Concentration of Credit Risk Financial instruments that potentially subject the Company to a concentration of credit risk consist of cash and cash equivalents, restricted cash and accounts receivable. Substantially all of the Company’s cash and cash equivalents and restricted cash are held with two financial institutions, and the account balances exceed the Federal Deposit Insurance Corporation (FDIC) insurance limit. Accounts are insured by the FDIC up to $250 per financial institution. The Company has not experienced any losses in such accounts with these financial institutions.
Concentration of Customers	Concentration of Customers For the year ended December 31, 2017, 2016 and 2015, there were no customers accounting for more than 10% of the Company’s revenue. As of December 31, 2017, two customers each accounted for 10% and 11% of the Company’s accounts receivable. As of December 31, 2016, six customers accounted for 10%, 11%, 11%, 11%, 12%, and 13% of the Company’s accounts receivable.
Allowance for Doubtful Accounts	Allowance for Doubtful Accounts Accounts receivable do not bear interest and are typically not collateralized. The Company performs ongoing credit evaluations of its customers and maintains reserves for potential credit losses. Accounts receivable are deemed past due in accordance with the contractual terms of the agreement. Accounts are charged against the allowance for doubtful accounts once collection efforts are unsuccessful. Historically, such losses have been within management's expectations. The allowance for doubtful accounts is $229 and $0 at December 31, 2017 and 2016.
Investments	Investments The Company determines the appropriate designation of its investments as “trading”, “available-for-sale” or “held-to-maturity” based on management’s intent at the time of purchase and reevaluates such designated at each reporting date. For all reporting periods presented, the Company’s investments are designated as available-for-sale. The Company determines any realized gains or losses on the sale of any investments on a specific identification method and records such gains and losses in the accompanying consolidated statements of operations. The Company evaluates its investments periodically for possible other-than-temporary impairment. A decline in fair value below the amortized cost of the investment is considered other-than-temporary impairment if the Company has the intent to sell the investment or it is more likely than not that the Company will be required to sell the investment before recovery of the entire amortized cost basis. In those instances, an impairment charge equal to the difference between the fair value and the amortized cost.
Inventory	Inventory Inventory is stated at the lower of cost or net realizable value and cost is principally determined using the first-in, first-out method. Costs include material, labor and overhead. Inventory that is obsolete or in excess of forecasted usage is written down to its estimated net realizable value based on assumptions about future demand and market conditions. Inventory write-downs are charged to cost of goods sold and a new cost basis for the inventory is established.
Concentration of Supplier	Concentration of Supplier The Company has a single source supplier manufacturing its system. If the supplier is not able to supply the requested orders, the Company would be unable to continue to derive revenue from the sale of systems until an alternative source is found, which could take a considerable length of time.
Property and Equipment	Property and Equipment Property and equipment are stated at cost, net of accumulated depreciation and amortization. Depreciation and amortization are computed using the straight-line method over the estimated useful lives of the assets, which is between three and five years. Leasehold improvements are amortized over the lesser of the life of the lease or the useful life of the improvements. Maintenance and repairs are charged to expense as incurred. When assets are retired or otherwise disposed of, the cost and accumulated depreciation are removed from the consolidated balance sheet, and any resulting gain or loss is reflected in operations.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets Long-lived assets are reviewed annually for impairment or whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. Recoverability is measured by comparison of the carrying amount to the future net undiscounted cash flows that the assets are expected to generate. If the carrying amount of an asset group exceeds its estimated future cash flows, an impairment charge is recognized in the amount by which the carrying amount of the asset group exceeds the fair value of the asset group. If such assets are considered to be impaired, the impairment to be recognized is measured by the amount by which the carrying amount of the assets exceeds the projected discounted future net cash flows arising from the asset. There has been no impairment of long-lived assets for any of the periods presented.
Preferred Stock Warrants Liabilities	Preferred Stock Warrants Liabilities The Company accounted for its freestanding warrants to purchase shares of convertible preferred stock that are contingently redeemable as liabilities in the consolidated balance sheets at their estimated fair value because these warrants may have obligated the Company to redeem them at some point in the future. At the end of each reporting period, changes in the estimated fair value of the warrants to purchase shares of convertible preferred stock were recorded as other income (expense), net in the consolidated statements of operations. Upon the closing of the IPO (as discussed in Note 1), all outstanding preferred stock warrants were converted into common stock warrants and the liability on the preferred stock warrants was reclassified to additional paid-in capital in stockholders’ equity (deficit) and was no longer subject to remeasurement.
Debt Issuance Costs	Debt Issuance Costs Costs related to the issuance of debt are presented as a direct deduction to the carrying value of the debt and are amortized to interest expense using the effective interest rate method over the term of the related debt.
Gain on Sale of Stock Investment	Gain on Sale of Stock Investment In the fourth quarter of 2017, the Company recognized a gain of $1,851 on the sale of stock held in a privately-held company that had been impaired and written-down to nil prior to fiscal year 2014.
Revenue Recognition	Revenue Recognition The Company generates revenue from sales of robotic systems and related procedures, and related support and maintenance. The Company derives revenue primarily from two sources: (i) Product revenue, which includes robotic systems sales, installation, software, procedure key and disposable kits; and (ii) Support and maintenance revenue, which includes support, training, and service contracts. Revenue is recognized when all of the following criteria are met: (l) persuasive evidence of an arrangement exists; (2) the product or service has been delivered; (3) the sales price is fixed or determinable; and (4) collection is reasonably assured. The Company defines each of the four criteria above as follows: • Persuasive Evidence of Arrangement Exists . The Company uses purchase orders pursuant to the terms and conditions of a master agreement to support the evidence of an arrangement with distributors and uses purchase agreements as evidence of arrangement with direct customers. • Delivery has Occurred . Provided that all other revenue recognition criteria have been met, for direct sales the Company typically recognizes system revenue upon customer acceptance, or upon shipment for systems sold to distributors, as title and risk of loss are transferred at that time, and there are no further obligations and no rights of return. Procedure revenue is recognized upon shipment of disposable kits and delivery of the ARTAS key. Support and maintenance revenue is recognized over time as the services are delivered. • The Sales Price is Fixed or Determinable . The Company assesses whether the fee is fixed or determinable based on the payment terms associated with the transaction. If the terms are extended beyond the Company’s normal payment terms, the Company will recognize revenue as the payments become due. Payments from distributors are not contingent on the distributors’ receiving payment from the end-users. • Collection is Reasonably Assured . The Company assesses probability of collection on an individual basis based on a number of factors, including the credit-worthiness of the customer and past transaction history with the customer. The Company generally obtains a significant cash deposit from its customers prior to shipment. The Company records its revenue net of sales tax and shipping and handling costs. Incremental direct costs incurred related to the acquisition or origination of a customer contract are expensed as incurred. Multiple Element Arrangements The Company’s offering includes robotic systems containing software components that function together to provide the essential functionality of the product. Therefore, the Company’s hardware products (inclusive of the core software) are considered non-software deliverables and are not subject to industry-specific software revenue recognition guidance. The Company’s typical multiple element arrangement includes robotic systems (including the essential software), procedure key, installation (for direct sales to end-users), product training and service contracts. The Company considers each of these deliverables to be separate units of accounting based on whether the delivered items have stand-alone value. The Company has determined that each unit of accounting has stand-alone value because they are sold separately by the Company or, for hardware products, because the customers can resell them to others on a stand-alone basis. For the arrangements with multiple deliverables, the Company allocates the arrangement fee to each element based upon the relative selling price of such element. When applying the relative selling price method, the Company determines the selling price for each element using vendor-specific objective evidence (VSOE) of selling price, if it exists, or if not, third-party evidence (TPE) of selling price, if it exists. If neither VSOE nor TPE of selling price exist for an element, the Company uses its best estimated selling price (BESP) for that element. The revenue allocated to each element is then recognized when the basic revenue recognition criteria are met for that element. The Company is not able to establish a selling price of its deliverables using VSOE or to determine TPE for its products and services. TPE is determined based on competitor prices for similar deliverables when sold separately. Generally, the Company’s go-to-market strategy differs from that of its peers and its offerings contain a significant level of differentiation such that the comparable pricing of products with similar functionality cannot be obtained. When the Company is unable to establish the selling price of its deliverables using VSOE or TPE, the Company uses BESP in its allocation of arrangement consideration. The objective of BESP is to determine the price at which the Company would transact a sale if the product or service were sold on a stand-alone basis. The Company determines BESP for a product or service by considering multiple factors including, but not limited to, industry and market conditions, competitive landscape, standard pricing practices and internal cost models. Additionally, the Company considers historical transactions, including transactions whereby the deliverable was sold on a stand-alone basis. Deferred revenue primarily relates to support and maintenance and pertains to billings or payments received in advance where all of the revenue recognition criteria have not been met. The current portion of deferred revenue represents the amounts that are expected to be recognized as revenue within one year of the consolidated balance sheet date.
Cost of Revenue	Cost of Revenue Cost of revenue consists of product and fulfillment costs. Product costs include the cost of systems and disposable kits manufacture, related labor and personnel costs and allocated shared costs. Fulfillment costs consist of costs incurred in the shipping and handling of inventory including the shipping costs to the Company's customers, labor and related personnel costs related to receiving, inspecting, warehousing, and preparing systems and reusable kits for shipment. Cost of revenue for customer service is expensed as incurred and primarily consists of personnel costs such as salaries, bonuses and benefits and stock‑based compensation for employees associated with service contracts, travel costs and allocated shared costs (including rent and information technology).
Research and Development	Research and Development Research and development costs are charged to operations as incurred.
Warranty	Warranty The Company provides a one-year warranty on the ARTAS System and accrues for the estimated future costs of repair or replacement upon customer acceptance or shipment. The warranty expense is accrued as a liability and recorded to cost of goods sold and is based upon historical information for the cost to repair or replace the system.
Sales Taxes	Sales Taxes Revenue is recorded net of taxes collected from customers that are remitted to governmental authorities with the collected taxes recorded as current liabilities in accrued and other liabilities in the accompanying consolidated balance sheets until remitted to the relevant government authority.
Income Taxes	Income Taxes Income taxes are accounted for under the asset and liability method. Deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the tax and financial reporting bases of the Company’s assets and liabilities. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in future years in which those temporary differences are expected to be recovered or settled. Deferred tax assets are reduced through the establishment of a valuation allowance, if, based upon available evidence, it is determined that it is more likely than not that the deferred tax assets will not be realized. All deferred tax assets and liabilities are classified as non-current in the consolidated financial statements. Uncertain Tax Positions The Company recognizes the effect of income tax positions only if those positions are more likely than not of being sustained on examination based on the technical merit of the position. The first step is to evaluate the tax position for recognition by determining if the weight of available evidence indicates it is more likely than not that the position will be sustained on examination, including resolution of related appeals or litigation processes, if any. The second step is to measure the tax benefit as the largest amount, which is more than 50% likely of being realized upon ultimate settlement. The Company considers many factors when evaluating and estimating its tax positions and tax benefits, which may require periodic adjustments. The Company recognizes interest charges and penalties related to unrecognized tax benefits as a component of the tax provision.
Stock-Based Compensation	Stock-Based Compensation U.S. GAAP requires the measurement and recognition of compensation expense for all share-based payment awards, including stock options, using a fair-value based method. The Company estimates the fair value of share-based payment awards on the date of grant using a Black-Scholes-Merton option-pricing model. Stock-based compensation is recognized on a straight-line basis over the requisite service period based on awards ultimately expected to vest. Forfeitures are estimated at the time of grant and revised, if necessary, in subsequent periods if actual forfeitures differ from those estimates. Stock-based awards granted to non-employees are accounted for at fair value. The associated expense is recognized by the Company over the period the services are performed by non-employees. The fair value of stock-based awards granted to non-employees was nominal for the years ended December 31, 2017, 2016 and 2015.
Net Loss Per Share Attributable to Common Stockholders	Net Loss Per Share Prior to the convervsion of all the preferred stock in connection with the IPO, the Company followed a two‑class method when computing net loss per common share as we issue shares that meet the definition of participating securities. The two‑class method determines net income (loss) per common share for each class of common stock and participating securities according to dividends declared or accumulated and participation rights in undistributed earnings. The two‑class method requires income for the period to be allocated between common stock and participating securities based upon their respective rights to receive dividends as if all income for the period had been distributed. Our convertible preferred stock contractually entitles the holders of such shares to participate in dividends, but does not contractually require the holders of such shares to participate in our losses. For periods in which the Company has reported net losses, diluted net loss per common share attributable to common stockholders is the same as basic net loss per common share attributable to common stockholders, because potentially dilutive common shares are not assumed to have been issued if their effect is anti‑dilutive.
Defined Contribution Plan	Defined Contribution Plan In 2006, the Company adopted a defined contribution retirement savings plan under Section 401(k) of the Internal Revenue Code (IRC). This plan covers employees who meet minimum age and service requirements and allows participants to defer a portion of their annual compensation on a pre-tax basis. Company contributions to the plan may be made at the discretion of the Board of Directors. There were no contributions by the Company during the years ended December 31, 2017, 2016 and 2015.
Jobs Act Accounting Election	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 is (i) no longer an emerging growth company or (ii) affirmatively and irrevocably opt out of the extended transition period provided in the JOBS Act. As a result, these consolidated financial statements may not be comparable to companies that comply with the new or revised accounting pronouncements as of public company effective dates.
Recently Issued Accounting Standards	Recently Issued Accounting Standards In May 2014, the FASB issued ASU No. 2014‑09, Revenue from Contracts with Customers The Company’s preliminary assessment of areas to be impacted by the new standard identified possible impact to the deferral of costs to obtain a contract, which are primarily commission expense directly incurred as a result of sales of products and related support, and the allocation of revenue between products and support and maintenance for certain arrangements. While the Company continues to assess the potential impact of the new standard, including the areas described above, it has not yet quantified the impact the new standard may have on its consolidated financial statements. In February 2016, the FASB issued ASU No. 2016‑02, Leases (Topic 842), or ASU 2016‑02, which requires lessees to record most leases on their balance sheets but recognize the expenses on their income statements in a manner similar to current practice. Under ASU 2016‑02, a lessee would recognize a lease liability for the obligation to make lease payments and a right‑to‑use asset for the right to use the underlying asset for the lease term. For public entities, this standard is effective for annual reporting periods beginning after December 15, 2018, including interim periods within that reporting period. For all other entities, this standard is 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 impact and materiality that this standard will have on its consolidated financial statements. However, the Company does expect an increase in its consolidated assets and liabilities upon adoption of this standard. Recently Adopted Accounting Standards In May 2017, the FASB issued ASU No. 2017-09 (Topic 718) Compensation—Stock Compensation: Scope of Modification Accounting, which provides guidance on the types of changes to the terms or conditions of share-based payment awards to which an entity would be required to apply modification accounting. The new standard is effective on a prospective basis for interim and annual periods beginning after December 15, 2017, with early adoption permitted. The Company early adopted this ASU on a prospective basis in the fourth quarter of fiscal 2017. Prior periods were not retrospectively adjusted. The adoption of the ASU did not have a material impact on the consolidated financial statements. In November 2016, the FASB issued ASU No. 2016-18 (Topic 230) Statement of Cash Flow: Restricted Cash, which provides guidance on the classification of restricted cash to be included with cash and cash equivalents when reconciling the beginning of period and end of period total amounts on the statement of cash flows. The amendments of this ASU are effective for interim and annual periods beginning after December 15, 2017, with early adoption permitted. The standard must be applied retrospectively to all periods presented. The Company has early adopted this standard in the fourth quarter of fiscal 2017 and the adoption did not have a material impact on its consolidated financial statements. In August 2016, the FASB issued ASU No. 2016‑15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments, or ASU 2016‑15. ASU 2016-15 identifies how certain cash receipts and cash payments are presented and classified in the Statement of Cash Flows. For public entities, this standard is effective for annual reporting periods beginning after December 15, 2017, including interim periods within that reporting period. For all other entities, this standard is effective for annual reporting periods beginning after December 15, 2018, and interim periods within annual periods beginning after December 15, 2019. This standard should be applied retrospectively and early adoption is permitted, including adoption in an interim period. The Company has early adopted this standard in the fourth quarter of fiscal 2017 and the adoption did not have a material impact on its consolidated financial statements. In March 2016, the FASB issued ASU No. 2016‑09, Compensation – Stock Compensation (Topic 718): Improvements to Employee Share‑Based Payment Accounting, or ASU 2016‑09. ASU 2016-09 simplifies the accounting and reporting of share‑based payment transactions, including adjustments to how excess tax benefits and payments for tax withholdings should be classified and provides the election to eliminate the estimate for forfeitures. For public entities, this standard is effective for annual reporting periods beginning after December 15, 2016, including interim periods within that reporting period. For all other entities, this standard is effective for annual reporting periods beginning after December 15, 2017, and interim periods within annual periods beginning after December 15, 2018. Early adoption is permitted for any entity in any interim or annual period for which financial statements have not been issued or made available for issuance. The Company early adopted this ASU on a prospective basis in the fourth quarter of fiscal 2017. Prior periods were not retrospectively adjusted. The adoption of the ASU did not have a material impact on the consolidated financial statements. In July 2015, the FASB issued ASU No. 2015-11, Inventory, Simplifying the Measurement of Inventory (Topic 330), or ASU 2015-11. Under ASU 2015-11, the measurement principle for inventory will change from lower of cost or market value to lower of cost and net realizable value. Net realizable value is the estimated selling price in the ordinary course of business, less reasonably predictable costs of completion, disposal and transportation. For public entities, this standard is effective for annual reporting periods beginning after December 15, 2016, including interim periods within that reporting period. For all other entities, this standard is effective for annual reporting periods beginning after December 15, 2016, and interim periods within annual periods beginning after December 15, 2017. This standard should be applied prospectively and early adoption is permitted. The Company adopted this ASU on a prospective basis in the fourth quarter of fiscal 2017. Prior periods were not retrospectively adjusted. The adoption of the ASU did not have a material impact on the consolidated financial statements.

Summary of Significant Accoun25

Summary of Significant Accounting Policies (Policies) (Tables)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Reconciliation of Cash, Cash Equivalents and Restricted Cash Reported	The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the balance sheets that sum to the total of the same amounts shown in the statements of cash flows. December 31, 2017 2016 Cash and cash equivalents $ 23,545 $ 11,906 Restricted cash 100 100 Total cash, cash equivalents and restricted cash in the consolidated statements of cash flows $ 23,645 $ 12,006

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	12 Months Ended
	Dec. 31, 2017
Earnings Per Share [Abstract]
Outstanding Shares of Common Stock Equivalents Excluded from Calculation of Diluted Net Loss per Share Attributable to Common Stockholders	Due to the net loss, all the outstanding shares of common stock equivalents were excluded from the calculation of diluted net loss per share attributable to common stockholders for the periods presented because including them would have been antidilutive: As of December 31, 2017 2016 2015 Options to purchase common stock 1,930,752 1,831,757 1,410,708 Convertible preferred stock — 21,142,295 19,336,777 Warrants for preferred stock — 385,126 385,126 Warrants for common stock 306,456 — — Total potential dilutive shares 2,237,208 23,359,178 21,132,611

Fair Value Measurements - (Tabl

Fair Value Measurements - (Tables)	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Schedule for Levels of Fair Value Measurements of Cash Equivalents, Investments and Preferred Stock Warrants Liabilities	The following tables summarize the levels of fair value measurements of the Company’s cash equivalents, investments and preferred stock warrants liabilities: Fair Value Measurements as of December 31, 2017 Quoted Prices in Active Markets using Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total Assets Cash Equivalents: Money market accounts $ 23,545 $ — $ — $ 23,545 Restricted cash 100 — — 100 Total assets $ 23,645 $ — $ — $ 23,645 Fair Value Measurements as of December 31, 2016 Quoted Prices in Active Markets using Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total Assets Cash Equivalents: Money market accounts $ 11,906 $ — $ — $ 11,906 Restricted cash 100 — — 100 Total assets $ 12,006 $ — $ — $ 12,006 Liabilities Preferred stock warrant liabilities $ — $ — $ 693 $ 693
Schedule of Preferred Stock Warrant Liabilities Activity Subject to Level 3 Inputs Measured on Recurring Basis	The following table summarizes the preferred stock warrant liabilities activity subject to Level 3 inputs which are measured on a recurring basis until their exercises: Fair value measurements of warrants using significant unobservable inputs (Level 3) Balance as of January 1, 2015 $ 659 Change in fair value of preferred stock warrants (578 ) Fair value of preferred stock warrants issued 266 Balance as of December 31, 2015 347 Change in fair value of preferred stock warrants 346 Balance as of December 31, 2016 693 Change in fair value of preferred stock warrants 387 Fair value of preferred stock warrants converted to common stock warrants (1,080 ) Balance as of December 31, 2017 $ —

Balance Sheet Components (Table

Balance Sheet Components (Tables)	12 Months Ended
	Dec. 31, 2017
Balance Sheet Components [Abstract]
Schedule of Inventory	Inventory December 31, 2017 2016 Finished goods $ 2,761 $ 2,580 Raw materials — 162 Total inventory $ 2,761 $ 2,742
Schedule of Property and Equipment, Net	Property December 31, 2017 2016 Computer hardware and software $ 721 $ 647 Equipment 2,929 2,818 Leasehold improvements 869 1,094 Furniture and fixtures 270 82 Total property and equipment 4,789 4,641 Less: Accumulated depreciation and amortization (3,651 ) (3,182 ) Total property and equipment, net $ 1,138 $ 1,459
Schedule of Accrued and Other Liabilities	Accrued December 31, 2017 2016 Payroll and related expense $ 1,630 $ 1,647 Other* 1,125 791 Total accrued and other liabilities $ 2,755 $ 2,438 * Other consists of items that are individually less than 5% of total current liabilities.

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2017
Commitments And Contingencies Disclosure [Abstract]
Summary of Aggregate Future Minimum Lease Payments under Operating Leases	Aggregate future minimum lease payments required under the Company’s operating leases as of December 31, 2017 are as follows: Years ending December 31, 2018 $ 503 2019 518 2020 534 2021 550 Thereafter 188 Total future minimum lease payments $ 2,293

Long-Term Debt (Tables)

Long-Term Debt (Tables)	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Schedule Principal Payments on Outstanding Borrowings	The scheduled principal payments on the outstanding borrowings as of December 31, 2017 are as follows: As of December 31, 2017 2018 $ 8,000 2019 5,300 Total 13,300 Less debt discount (299 ) Less current portion (7,730 ) Non-current portion $ 5,271

Preferred Stock (Tables)

Preferred Stock (Tables)	12 Months Ended
	Dec. 31, 2017
Temporary Equity Disclosure [Abstract]
Schedule of Convertible Preferred Stock	The convertible preferred stock as of December 31, 2016 consisted of the following: December 31, 2016 Convertible Preferred Stock: Shares Authorized Shares Outstanding Net Carrying Value Liquidation Preference Series A 25,092,906 2,509,232 $ 11,140 $ 11,292 Series B 38,461,538 3,846,132 24,926 25,000 Series C 170,100,000 14,536,931 97,693 103,939 Series AA 2,500,000 250,000 1,976 2,000 Total convertible preferred stock 236,154,444 21,142,295 $ 135,735 $ 142,231

Preferred and Common Stock Wa32

Preferred and Common Stock Warrants (Tables)	12 Months Ended
	Dec. 31, 2017
Summary of Preferred Stock Warrants	As of December 31, 2016, the preferred stock warrants consisted of the following: Warrants Outstanding December 31, 2016 Exercise Price Expiration Series C preferred stock warrants 274,640 $ 7.15 Various dates in 2023 - 2024 Series C preferred stock warrants 110,486 7.15 May 19, 2025 Total preferred stock warrants 385,126
Assumptions of Fair Value Preferred Stock Warrants	The estimated Year Ended December 31, 2017 2016 2015 Expected term (in years) 4.95-7.50 5.53–6.11 5.00 – 6.07 Risk-free interest rate 1.77-2.13% 1.30–1.84% 1.47– 1.82% Expected volatility 51.62-55.38% 52.71–56.58% 51.93-58.21% Expected dividend rate 0% 0% 0%
Preferred Stock Warrants
Assumptions of Fair Value Preferred Stock Warrants	The fair value of preferred stock warrants was determined using the following assumptions: Year Ended December 31 2016 Expected term (years) 2.00 Risk-free interest rate 1.20 % Expected volatility 70.90 % The Company estimated the fair value of the preferred stock warrant liability using the Black-Scholes-Merton Expected term (years) 1.00-7.61 Risk-free interest rate 1.31-2.16% Expected volatility 72%

Common Stock Reserved For Iss33

Common Stock Reserved For Issuance (Tables)	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Schedule of Effect the Conversion of All Outstanding Shares of Convertible Preferred Stock Under the Incentive Plans	The Company is 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 of all outstanding shares of convertible preferred stock (and preferred stock warrants), plus options granted and available for grant under the incentive plans. December 31, 2017 December 31, 2016 Conversion of outstanding Series A convertible preferred stock — 2,509,232 Conversion of outstanding Series B convertible preferred stock — 3,846,132 Conversion of outstanding Series C convertible preferred stock — 14,536,931 Conversion of outstanding Series AA convertible preferred stock — 250,000 Outstanding preferred stock warrants — 385,126 Outstanding common stock warrants 306,456 — Outstanding and issued stock options 1,930,752 1,831,757 Shares reserved for future option grants 271,490 392,306 Total common stock reserved for issuance 2,508,698 23,751,484

Stock Option Plan (Tables)

Stock Option Plan (Tables)	12 Months Ended
	Dec. 31, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Summary of Recognized Stock-based Compensation Expense for Employees and Non-employees	The Company recognized stock-based compensation for its employees and non-employees in the accompanying consolidated statements of operations as follows: Year Ended December 31, 2017 2016 2015 Cost of revenue $ 10 $ 12 $ 12 Research and development 101 102 116 Sales and marketing 74 85 140 General and administrative 280 267 161 Total stock-based compensation $ 465 $ 466 $ 429
Assumptions of Fair Value Preferred Stock Warrants	The estimated Year Ended December 31, 2017 2016 2015 Expected term (in years) 4.95-7.50 5.53–6.11 5.00 – 6.07 Risk-free interest rate 1.77-2.13% 1.30–1.84% 1.47– 1.82% Expected volatility 51.62-55.38% 52.71–56.58% 51.93-58.21% Expected dividend rate 0% 0% 0%
Summary of Stock Option Activity	The following table summarizes stock option activity under the Company’s stock option plan: Number of Shares Weighted- Average Exercise Price per Share Weighted- Average Remaining Contractual Term Aggregate Intrinsic Value Outstanding – January 1, 2015 1,258,429 $ 1.80 Options granted 532,930 1.80 Options exercised (79,893 ) 1.40 Options cancelled (294,654 ) 1.40 Options expired (6,104 ) 2.30 Outstanding – December 31, 2015 1,410,708 1.90 7.9 $ — Options granted 1,179,644 1.70 Options exercised (20,218 ) 2.00 Options cancelled (737,377 ) 2.00 Options expired (1,000 ) 0.50 Outstanding – December 31, 2016 1,831,757 1.80 8.7 $ 14 Options granted 192,420 3.12 Options exercised (21,843 ) 2.01 Options cancelled (71,582 ) 1.81 Outstanding – December 31, 2017 1,930,752 $ 1.90 7.9 $ 5,322 Vested and expected to vest – December 31, 2017 1,667,332 $ 1.90 7.8 $ 4,590 Exercisable – December 31, 2017 960,933 $ 1.80 7.2 $ 3,257

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Schedule of Geographical Breakdown of Loss Before Provision for Income Taxes	The geographical breakdown of loss before provision for income taxes is as follows: Year Ended December 31, 2017 2016 2015 Domestic $ (17,732 ) $ (21,696 ) $ (22,535 ) Foreign (54 ) (150 ) (436 ) Net loss before provision for income taxes $ (17,786 ) $ (21,846 ) $ (22,971 )
Schedule of Components of Provision for Income Taxes	The components of the provision for income taxes are as follows: Year Ended December 31, 2017 2016 2015 Current tax provision: Federal $ — $ — $ — State 4 4 4 Foreign 56 16 17 Total current tax provision 60 20 21 Deferred tax provision (benefit): State (4 ) (4 ) (4 ) Foreign — (16 ) (17 ) Total deferred tax provision (benefit) $ (4 ) $ (20 ) $ (21 ) Total provision for income taxes $ 56 $ — $ —
Reconciliation between Income Taxes Computed at Federal Statutory Income Tax Rate and Provision for Income Taxes	The reconciliation between income taxes computed at the federal statutory income tax rate and the provision for income taxes is as follows Year Ended December 31, 2017 2016 2015 U.S. federal statutory income tax at 34% $ (6,046 ) $ (7,306 ) $ (7,973 ) Research tax credits (75 ) (99 ) (82 ) Stock-based compensation 85 102 125 Adjustment of deferred tax balances following changes in tax rates 20,748 — — Other 303 117 599 Change in valuation allowance (14,955 ) 7,206 7,352 Total current tax provision 60 20 21 Total deferred tax benefit (4 ) (20 ) (21 ) Total provision for income taxes $ 56 $ — $ —
Schedule of Components of Deferred Tax Assets	The components of the deferred tax assets are as follows: December 31, 2017 2016 Deferred tax assets: Net operating loss carryforwards $ 37,173 $ 51,104 Research and development credits 2,823 2,456 Accrual and reserves 1,251 1,575 Total deferred tax assets 41,247 55,135 Less: valuation allowance (41,247 ) (55,135 ) Total net deferred tax assets $ — $ —
Schedule of Reconciliation of Uncertain Tax Position	The activity related to the gross amount of unrecognized tax benefits is as follows: Year Ended December 31, 2017 2016 Balance as of the beginning of the year $ 1,283 $ 1,186 Increases related to tax positions in prior period 5 16 Increases related to tax positions taken during the current period 74 81 Balance at the end of the year $ 1,362 $ 1,283

Geographic Information (Tables)

Geographic Information (Tables)	12 Months Ended
	Dec. 31, 2017
Segment Reporting [Abstract]
Schedule of Revenue by Geographic Area	The following Year Ended December 31, 2017 2016 2015 United States $ 8,919 $ 6,736 $ 8,252 Europe and Middle East 5,784 3,112 2,940 Asia Pacific 4,353 3,552 2,989 Rest of World 2,241 2,200 3,049 Total revenue $ 21,297 $ 15,600 $ 17,230

Selected Quarterly Financial 37

Selected Quarterly Financial Data (Tables)	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Data [Abstract]
Schedule of Selected Quarterly Financial Data	The following tables present certain selected unaudited consolidated quarterly financial information for each of the eight quarters ended December 31, 2017. This consolidated quarterly information has been prepared on the same basis as the consolidated financial statements and includes all adjustments necessary to state fairly the information for the periods presented. The selected consolidated quarterly financial results from operations for the years ended December 31, 2017 and 2016 are set forth therein. Net loss per share for all periods presented has been retroactively adjusted to reflect the 1-for-10 reverse stock split effected on September 15, 2017. Fiscal 2017 Quarter Ended, March 31, 2017 Unaudited June 30, 2017 Unaudited September 30, 2017 Unaudited December 31, 2017 Unaudited Revenue, net $ 5,475 $ 5,789 $ 4,177 $ 5,856 Gross profit $ 2,383 $ 2,302 $ 1,703 $ 2,759 Net loss $ (5,175 ) $ (5,007 ) $ (6,596 ) $ (1,064 ) Basic and diluted net loss per share $ (3.20 ) $ (3.09 ) $ (4.07 ) $ (0.04 ) Fiscal 2016 Quarter Ended, March 31, 2016 Unaudited June 30, 2016 Unaudited September 30, 2016 Unaudited December 31, 2016 Unaudited Revenue, net $ 3,187 $ 3,559 $ 3,676 $ 5,178 Gross profit $ 779 $ 1,104 $ 1,272 $ 2,014 Net loss $ (5,814 ) $ (5,172 ) $ (5,928 ) $ (4,932 ) Basic and diluted net loss per share $ (3.61 ) $ (3.21 ) $ (3.67 ) $ (3.06 )

Nature of Operations - Addition

Nature of Operations - Additional Information (Details) $ / shares in Units, $ in Thousands	Oct. 16, 2017USD ($)$ / sharesshares	Sep. 15, 2017	Dec. 31, 2017USD ($)$ / sharesshares	Dec. 31, 2016$ / sharesshares
Nature of Operations [Line Items]
Aggregate proceeds from initial public offering, after deducting underwriter discounts and commission | $			$ 22,114
Capital stock, authorized	310,000,000
Common stock, shares authorized	300,000,000		300,000,000	350,490,000
Preferred stock, shares authorized	10,000,000		10,000,000	0
Preferred stock, par value | $ / shares	$ 0.0001		$ 0.0001	$ 0.0001
Common stock, par value | $ / shares	$ 0.0001		$ 0.0001	$ 0.0001
Reverse stock split of common stock, description		1-for-10 reverse stock split
Reverse stock split of common stock, ratio		0.1
IPO
Nature of Operations [Line Items]
Number of common stock shares issued	3,897,910
Shares issued price per share | $ / shares	$ 7
Aggregate proceeds from initial public offering, after deducting underwriter discounts and commission | $	$ 22,114
Offering costs | $	$ 5,171
Outstanding shares of convertible preferred stock converted into common stock	22,671,601
IPO | Subordinated Convertible Notes
Nature of Operations [Line Items]
Outstanding convertible notes converted into common stock	718,184
Over-Allotment Option
Nature of Operations [Line Items]
Number of common stock shares issued	322,910

Summary of Significant Accoun39

Summary of Significant Accounting Policies - Additional Information (Details)	3 Months Ended	12 Months Ended
	Dec. 31, 2017USD ($)Institution	Dec. 31, 2017USD ($)SegmentInstitutionCustomer	Dec. 31, 2016USD ($)Customer	Dec. 31, 2015USD ($)Customer
Summary Of Significant Accounting Policies [Line Items]
Accumulated deficit	$ (164,487,000)	$ (164,487,000)	$ (146,645,000)
Number of operating segments | Segment		1
Number of reportable segments | Segment		1
Impairment of long-lived assets		$ 0
Gain on sale of stock investment	$ 1,851,000	$ 1,851,000
Deferred revenue expected recognized period		1 year
Warrant period on ARTAS system accrues estimated future costs of repair		1 year
Effective tax benefit realized upon ultimate settlement		50.00%
Board of Directors
Summary Of Significant Accounting Policies [Line Items]
Defined contribution plan employer contribution amount		$ 0	$ 0	$ 0
Minimum | Property and Equipment
Summary Of Significant Accounting Policies [Line Items]
Depreciation and amortization, estimated useful lives of assets		3 years
Maximum | Property and Equipment
Summary Of Significant Accounting Policies [Line Items]
Depreciation and amortization, estimated useful lives of assets		5 years
Credit Concentration Risk
Summary Of Significant Accounting Policies [Line Items]
Number of financial institution | Institution	2	2
Credit Concentration Risk | Maximum
Summary Of Significant Accounting Policies [Line Items]
FDIC insured amount	$ 250,000	$ 250,000
Customer Concentration Risk | Revenue
Summary Of Significant Accounting Policies [Line Items]
Number of major customers | Customer		0	0	0
Customer Concentration Risk | Accounts Receivable
Summary Of Significant Accounting Policies [Line Items]
Number of major customers | Customer		2	6
Allowance for doubtful accounts	229,000	$ 229,000	$ 0
Customer Concentration Risk | Customer One | Accounts Receivable
Summary Of Significant Accounting Policies [Line Items]
Concentration risk, percentage		10.00%	10.00%
Customer Concentration Risk | Customer Two | Accounts Receivable
Summary Of Significant Accounting Policies [Line Items]
Concentration risk, percentage		11.00%	11.00%
Customer Concentration Risk | Customer Three | Accounts Receivable
Summary Of Significant Accounting Policies [Line Items]
Concentration risk, percentage			11.00%
Customer Concentration Risk | Customer Four | Accounts Receivable
Summary Of Significant Accounting Policies [Line Items]
Concentration risk, percentage			11.00%
Customer Concentration Risk | Customer Five | Accounts Receivable
Summary Of Significant Accounting Policies [Line Items]
Concentration risk, percentage			12.00%
Customer Concentration Risk | Customer Six | Accounts Receivable
Summary Of Significant Accounting Policies [Line Items]
Concentration risk, percentage			13.00%
Collateral for Credit Cards | Other Assets
Summary Of Significant Accounting Policies [Line Items]
Restricted cash	$ 100,000	$ 100,000	$ 100,000

Summary of Significant Accoun40

Summary of Significant Accounting Policies - Reconciliation of Cash, Cash Equivalents and Restricted Cash Reported (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accounting Policies [Abstract]
Cash and cash equivalents	$ 23,545	$ 11,906
Restricted cash	100	100
Total cash, cash equivalents and restricted cash in the consolidated statements of cash flows	$ 23,645	$ 12,006	$ 17,227	$ 32,900

Net Loss Per Share - Outstandin

Net Loss Per Share - Outstanding Shares of Common Stock Equivalents Excluded from Calculation of Diluted Net Loss per Share Attributable to Common Stockholders (Details) - shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Total potential dilutive shares	2,237,208	23,359,178	21,132,611
Options to Purchase Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Total potential dilutive shares	1,930,752	1,831,757	1,410,708
Warrants for Preferred Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Total potential dilutive shares		385,126	385,126
Warrants for Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Total potential dilutive shares	306,456
Convertible Preferred Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Total potential dilutive shares		21,142,295	19,336,777

Fair Value Measurements - Sched

Fair Value Measurements - Schedule for Levels of Fair Value Measurements of Cash Equivalents, Investments and Preferred Stock Warrants Liabilities - (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total assets	$ 23,645	$ 12,006
Preferred Stock Warrant Liabilities
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Liabilities		693
Quoted Prices in Active Markets using Identical Assets (Level 1)
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total assets	23,645	12,006
Significant Unobservable Inputs (Level 3) | Preferred Stock Warrant Liabilities
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Liabilities		693
Money Market Accounts
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash Equivalents	23,545	11,906
Money Market Accounts | Quoted Prices in Active Markets using Identical Assets (Level 1)
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash Equivalents	23,545	11,906
Restricted Cash
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash Equivalents	100	100
Restricted Cash | Quoted Prices in Active Markets using Identical Assets (Level 1)
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash Equivalents	$ 100	$ 100

Fair Value Measurements - Sch43

Fair Value Measurements - Schedule of Preferred Stock Warrant Liabilities Activity Subject to Level 3 Inputs Measured on Recurring Basis - (Details) - Preferred Stock Warrant Liabilities - Significant Unobservable Inputs (Level 3) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning balance	$ 693	$ 347	$ 659
Change in fair value of preferred stock warrants	387	346	(578)
Fair value of preferred stock warrants issued			266
Fair value of preferred stock warrants converted to common stock warrants	$ (1,080)
Ending balance		$ 693	$ 347

Balance Sheet Components - Sche

Balance Sheet Components - Schedule of Inventory (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Inventory Disclosure [Abstract]
Finished goods	$ 2,761	$ 2,580
Raw materials		162
Total inventory	$ 2,761	$ 2,742

Balance Sheet Components - Sc45

Balance Sheet Components - Schedule of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Property Plant And Equipment [Abstract]
Computer hardware and software	$ 721	$ 647
Equipment	2,929	2,818
Leasehold improvements	869	1,094
Furniture and fixtures	270	82
Total property and equipment	4,789	4,641
Less: Accumulated depreciation and amortization	(3,651)	(3,182)
Total property and equipment, net	$ 1,138	$ 1,459

Balance Sheet Components - Addi

Balance Sheet Components - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property Plant And Equipment [Abstract]
Depreciation and amortization	$ 574	$ 654	$ 860

Balance Sheet Components - Sc47

Balance Sheet Components - Schedule of Accrued and Other Liabilities (Details) - USD ($) $ in Thousands		Dec. 31, 2017	Dec. 31, 2016
Payables And Accruals [Abstract]
Payroll and related expense		$ 1,630	$ 1,647
Other	[1]	1,125	791
Total accrued and other liabilities		$ 2,755	$ 2,438
[1]	Other consists of items that are individually less than 5% of total current liabilities.

Balance Sheet Components - Sc48

Balance Sheet Components - Schedule of Accrued and Other Liabilities (Parenthetical) (Details)	Dec. 31, 2017	Dec. 31, 2016
Maximum
Accrued Expenses And Other Liabilities [Line Items]
Percentage on other accrued liabilities of current liabilities	5.00%	5.00%

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details) $ in Thousands	1 Months Ended		12 Months Ended
	Feb. 29, 2012USD ($)	Jul. 31, 2006USD ($)shares	Dec. 31, 2017USD ($)ft²	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Commitment And Contingencies [Line Items]
Rent expense in operating leases			$ 413	$ 315	$ 322
Rassman Licensing, LLC
Commitment And Contingencies [Line Items]
License agreement termination date		May 9, 2020
Rassman Licensing, LLC | License Agreement
Commitment And Contingencies [Line Items]
One time payment of royalty related to license	$ 400	$ 1,000
Royalty expense			$ 0	$ 0	$ 0
HSC Development, LLC
Commitment And Contingencies [Line Items]
License agreement termination date		Jul. 27, 2024
HSC Development, LLC | License Agreement
Commitment And Contingencies [Line Items]
One time payment of royalty related to license		$ 25
Number of common stock shares issued | shares		2,500
San Jose, California
Commitment And Contingencies [Line Items]
Operating lease office space area | ft²			23,000
Operating lease expiration date			2022-04

Commitments and Contingencies50

Commitments and Contingencies - Summary of Aggregate Future Minimum Lease Payments under Operating Leases (Details) $ in Thousands	Dec. 31, 2017USD ($)
Commitments And Contingencies Disclosure [Abstract]
2,018	$ 503
2,019	518
2,020	534
2,021	550
Thereafter	188
Total future minimum lease payments	$ 2,293

Long-Term Debt - Additional Inf

Long-Term Debt - Additional Information (Details) - USD ($)	Oct. 16, 2017	May 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Sep. 06, 2017	Jan. 31, 2015
Debt Instrument [Line Items]
Net deferred debt costs			$ 299,000
Repayments of long-term debt			8,000,000	$ 0	$ 15,000,000
IPO
Debt Instrument [Line Items]
Shares issued price per share	$ 7
Loan and Security Agreement | Oxford Finance, LLC
Debt Instrument [Line Items]
Debt instrument, borrowed amount		$ 20,000,000
Credit facility fees							$ 246,000
Net deferred debt costs							$ 153,000
Debt Instrument, maturity month and year		2019-07
Debt instrument, final payment amount upon maturity		$ 1,300,000
Debt instrument, outstanding principal balance			13,300,000
Debt instrument, accrued interest			$ 85,000
Debt instrument, interest rate			13.00%
Loan and Security Agreement | Oxford Finance, LLC | Series C Convertible Preferred Stock
Debt Instrument [Line Items]
Debt conversion, warrants issued		110,486
Shares issued price per share		$ 7.15
Loan and Security Agreement | Oxford Finance, LLC | Warrants for Preferred Stock
Debt Instrument [Line Items]
Debt instrument, term		10 years
Loan and Security Agreement | Oxford Finance, LLC | Prime Rate
Debt Instrument [Line Items]
Debt instrument, stated Interest rate		8.50%
Subordinated Convertible Notes | Private Placement
Debt Instrument [Line Items]
Debt instrument, borrowed amount						$ 5,000,000
Debt instrument, stated Interest rate						5.00%
Subordinated Convertible Notes | IPO
Debt Instrument [Line Items]
Debt instrument, outstanding principal balance			$ 0
Outstanding convertible notes converted into common stock	718,184

Long-Term Debt - Schedule Princ

Long-Term Debt - Schedule Principal Payments on Outstanding Borrowings (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Debt Disclosure [Abstract]
2,018	$ 8,000
2,019	5,300
Total	13,300
Less debt discount	(299)
Less current portion	(7,730)	$ (7,449)
Non-current portion	$ 5,271	$ 13,001

Preferred Stock - Additional In

Preferred Stock - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Oct. 16, 2017
Temporary Equity [Line Items]
Preferred stock, shares authorized	10,000,000	0		10,000,000
Preferred stock, par value	$ 0.0001	$ 0.0001		$ 0.0001
Preferred stock, shares outstanding	0	0
IPO
Temporary Equity [Line Items]
Outstanding shares of convertible preferred stock converted into common stock				22,671,601
Series C Convertible Preferred Stock
Temporary Equity [Line Items]
Issuance of convertible preferred stock, shares	1,529,306	1,805,518	674,252
Issuance of convertible preferred stock for net cash proceeds	$ 10,209	$ 12,073	$ 4,175
Issuance of convertible preferred stock, net of issuance cost	$ 726	$ 837	$ 646

Preferred Stock - Schedule of C

Preferred Stock - Schedule of Convertible Preferred Stock (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Temporary Equity [Line Items]
Shares Authorized	0	236,154,444
Shares Outstanding	0	21,142,295
Net Carrying Value		$ 135,735
Aggregate liquidation preference	$ 0	$ 142,231
Series A Convertible Preferred Stock
Temporary Equity [Line Items]
Shares Authorized		25,092,906
Shares Outstanding		2,509,232
Net Carrying Value		$ 11,140
Aggregate liquidation preference		$ 11,292
Series B Convertible Preferred Stock
Temporary Equity [Line Items]
Shares Authorized		38,461,538
Shares Outstanding		3,846,132
Net Carrying Value		$ 24,926
Aggregate liquidation preference		$ 25,000
Series C Convertible Preferred Stock
Temporary Equity [Line Items]
Shares Authorized		170,100,000
Shares Outstanding		14,536,931
Net Carrying Value		$ 97,693
Aggregate liquidation preference		$ 103,939
Series A A Convertible Preferred Stock
Temporary Equity [Line Items]
Shares Authorized		2,500,000
Shares Outstanding		250,000
Net Carrying Value		$ 1,976
Aggregate liquidation preference		$ 2,000

Preferred and Common Stock Wa55

Preferred and Common Stock Warrants - Summary of Preferred Stock Warrants (Details)	12 Months Ended
	Dec. 31, 2016$ / sharesshares
Class Of Warrant Or Right [Line Items]
Warrants outstanding	385,126
Series C Preferred Stock Warrants One
Class Of Warrant Or Right [Line Items]
Warrants outstanding	274,640
Warrants outstanding exercise price | $ / shares	$ 7.15
Warrants outstanding expiration date description	Various dates in 2023 - 2024
Series C Preferred Stock Warrants Two
Class Of Warrant Or Right [Line Items]
Warrants outstanding	110,486
Warrants outstanding exercise price | $ / shares	$ 7.15
Warrants outstanding expiration date	May 19, 2025

Preferred and Common Stock Wa56

Preferred and Common Stock Warrants - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Oct. 16, 2017	Oct. 15, 2017	Dec. 31, 2016
Class Of Warrant Or Right [Line Items]
Warrants balance			$ 0
Warrants outstanding				385,126
Fair value of preferred stock warrant liability		$ 1,080,000
Common Stock
Class Of Warrant Or Right [Line Items]
Warrants exercised net	78,670
Net exercise of common stock warrants shares	15,112
Warrants outstanding	306,456
Warrants outstanding exercise price	$ 7.15
Warrants outstanding expiration date description	2018 to 2025

Preferred and Common Stock Wa57

Preferred and Common Stock Warrants - Assumptions of Fair Value Preferred Stock Warrants (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Minimum
Class Of Warrant Or Right [Line Items]
Expected term (years)	4 years 11 months 12 days	5 years 6 months 10 days	5 years
Maximum
Class Of Warrant Or Right [Line Items]
Expected term (years)	7 years 6 months	6 years 1 month 9 days	6 years 25 days
Preferred Stock Warrants
Class Of Warrant Or Right [Line Items]
Expected term (years)		2 years
Risk-free interest rate		1.20%
Expected volatility	72.00%	70.90%
Preferred Stock Warrants | Minimum
Class Of Warrant Or Right [Line Items]
Expected term (years)	1 year
Risk-free interest rate	1.31%
Preferred Stock Warrants | Maximum
Class Of Warrant Or Right [Line Items]
Expected term (years)	7 years 7 months 9 days
Risk-free interest rate	2.16%

Common Stock Reserved For Iss58

Common Stock Reserved For Issuance - Schedule of Effect the Conversion of All Outstanding Shares of Convertible Preferred Stock Under the Incentive Plans (Details) - shares	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Class Of Stock [Line Items]
Warrants outstanding		385,126
Outstanding and issued stock options	1,930,752	1,831,757	1,410,708	1,258,429
Shares reserved for future option grants	271,490	392,306
Total common stock reserved for issuance	2,508,698	23,751,484
Series A Convertible Preferred Stock
Class Of Stock [Line Items]
Conversion of outstanding preferred stock		2,509,232
Series B Convertible Preferred Stock
Class Of Stock [Line Items]
Conversion of outstanding preferred stock		3,846,132
Series C Convertible Preferred Stock
Class Of Stock [Line Items]
Conversion of outstanding preferred stock		14,536,931
Series A A Convertible Preferred Stock
Class Of Stock [Line Items]
Conversion of outstanding preferred stock		250,000
Preferred Stock
Class Of Stock [Line Items]
Warrants outstanding		385,126
Common Stock
Class Of Stock [Line Items]
Warrants outstanding	306,456

Stock Option Plan - Additional

Stock Option Plan - Additional Information (Details) - USD ($)	Oct. 11, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares reserved for issuance		2,508,698	23,751,484
Expected dividend		$ 0
Weighted-average grant date fair value of options granted		$ 1.73	$ 0.86	$ 1.10
Total intrinsic value of options exercised		$ 1,180	$ 0	$ 47,000
Unamortized stock-based compensation		$ 722,000
Unamortized stock-based compensation, weighted-average period		2 years 7 months 17 days
2015 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares reserved for issuance	306,756
2017 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares reserved for issuance	1,913,831	2,220,587
Effective date of plan	Oct. 11, 2017
Annual increase in shares reserved for issuance beginning year	2,018
Annual increase in shares reserved for issuance ending year	2,027
Percentage threshold of increase in shares reserved for issuance	4.00%

Stock Option Plan - Summary of

Stock Option Plan - Summary of Recognized Stock-based Compensation Expense for Employees and Non-employees (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation	$ 465	$ 466	$ 429
Employees and Non-employees
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation	465	466	429
Cost of Revenue | Employees and Non-employees
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation	10	12	12
Research and Development | Employees and Non-employees
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation	101	102	116
Sales and Marketing | Employees and Non-employees
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation	74	85	140
General and Administrative | Employees and Non-employees
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation	$ 280	$ 267	$ 161

Stock Option Plan - Estimated G

Stock Option Plan - Estimated Grant-Date Fair Value of Stock-Based Awards Calculated Using Black-Scholes-Merton Option Pricing Model (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free interest rate, minimum	1.77%	1.30%	1.47%
Risk-free interest rate, maximum	2.13%	1.84%	1.82%
Expected volatility, minimum	51.62%	52.71%	51.93%
Expected volatility, maximum	55.38%	56.58%	58.21%
Expected dividend rate	0.00%	0.00%	0.00%
Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)	4 years 11 months 12 days	5 years 6 months 10 days	5 years
Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)	7 years 6 months	6 years 1 month 9 days	6 years 25 days

Stock Option Plan - Summary o62

Stock Option Plan - Summary of Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Roll Forward
Number of Shares, Outstanding, Beginning Balance	1,831,757	1,410,708	1,258,429
Number of Shares, Options granted	192,420	1,179,644	532,930
Number of Shares, Options exercised	(21,843)	(20,218)	(79,893)
Number of Shares, Options cancelled	(71,582)	(737,377)	(294,654)
Number of Shares, Options expired		(1,000)	(6,104)
Number of Shares, Outstanding, Ending Balance	1,930,752	1,831,757	1,410,708
Number of Shares, Vested and expected to vest	1,667,332
Number of Shares, Exercisable	960,933
Weighted-Average Exercise Price Per Share, Outstanding, Beginning Balance	$ 1.80	$ 1.90	$ 1.80
Weighted-Average Exercise Price Per Share, Options granted	3.12	1.70	1.80
Weighted-Average Exercise Price Per Share, Options exercised	2.01	2	1.40
Weighted-Average Exercise Price Per Share, Options cancelled	1.81	2	1.40
Weighted-Average Exercise Price Per Share, Options expired		0.50	2.30
Weighted-Average Exercise Price Per Share, Outstanding, Ending Balance	1.90	$ 1.80	$ 1.90
Weighted-Average Exercise Price Per Share, Vested and expected to vest	1.90
Weighted-Average Exercise Price Per Share, Exercisable	$ 1.80
Weighted-Average Remaining Contractual Term, Outstanding	7 years 10 months 24 days	8 years 8 months 12 days	7 years 10 months 24 days
Weighted-Average Remaining Contractual Term, Vested and expected to vest	7 years 9 months 18 days
Weighted-Average Remaining Contractual Term, Exercisable	7 years 2 months 12 days
Aggregate Intrinsic Value, Outstanding	$ 5,322	$ 14
Aggregate Intrinsic Value, Vested and expected to vest	4,590
Aggregate Intrinsic Value, Exercisable	$ 3,257

Income Taxes - Schedule of Geog

Income Taxes - Schedule of Geographical Breakdown of Loss Before Provision for Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Domestic	$ (17,732)	$ (21,696)	$ (22,535)
Foreign	(54)	(150)	(436)
Net loss before provision for income taxes	$ (17,786)	$ (21,846)	$ (22,971)

Income Taxes - Schedule of Comp

Income Taxes - Schedule of Components of Provision for Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current tax provision:
State	$ 4	$ 4	$ 4
Foreign	56	16	17
Total current tax provision	60	20	21
Deferred tax provision (benefit):
State	(4)	(4)	(4)
Foreign		(16)	(17)
Total deferred tax provision (benefit)	(4)	$ (20)	$ (21)
Total provision for income taxes	$ 56

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Taxes [Line Items]
Deferred tax assets, valuation allowance, change in amount		$ (13,888,000)	$ 7,634,000
Federal statutory rate		34.00%	34.00%	34.00%
Maximum measurement period to complete effects of tax reform		12 months
Effect on the benefit from taxes on income due to the valuation allowance		$ 0
Deferred tax assets, federal operating loss carry forwards		154,250,000
Deferred tax assets, state operating loss carry forwards		$ 96,696,000
Operating loss carry forwards, expiry year start		2,018
Operating loss carry forwards, expiry year end		2,037
Federal research and development tax credit carryforwards		$ 1,490,000
State research and development tax credit carryforwards		$ 1,687,000
Federal research and development tax credit carryforwards, expiration starting year		2,025
Cumulative amount undistributed earnings		$ 122,000
Earliest Tax Year
Income Taxes [Line Items]
Tax year		2,002
Latest Tax Year
Income Taxes [Line Items]
Tax year		2,017
South Korea
Income Taxes [Line Items]
Operating loss carry forwards, expiry year end		2,025
Deferred tax assets, foreign operating loss carry forwards		$ 1,102,000
Scenario Plan
Income Taxes [Line Items]
Federal statutory rate	21.00%

Income Taxes - Reconciliation b

Income Taxes - Reconciliation between Income Taxes Computed at Federal Statutory Income Tax Rate and Provision for Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Effective Income Tax Rate Continuing Operations Tax Rate Reconciliation [Abstract]
U.S. federal statutory income tax	$ (6,046)	$ (7,306)	$ (7,973)
Research tax credits	(75)	(99)	(82)
Stock-based compensation	85	102	125
Adjustment of deferred tax balances following changes in tax rates	20,748
Other	303	117	599
Change in valuation allowance	(14,955)	7,206	7,352
Total current tax provision	60	20	21
Total deferred tax benefit	(4)	$ (20)	$ (21)
Total provision for income taxes	$ 56

Income Taxes - Reconciliation67

Income Taxes - Reconciliation between Income Taxes Computed at Federal Statutory Income Tax Rate and Provision for Income Taxes (Parenthetical) (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Effective Income Tax Rate Continuing Operations Tax Rate Reconciliation [Abstract]
Federal statutory rate	34.00%	34.00%	34.00%

Income Taxes - Schedule of Co68

Income Taxes - Schedule of Components of Deferred Tax Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
Net operating loss carryforwards	$ 37,173	$ 51,104
Research and development credits	2,823	2,456
Accrual and reserves	1,251	1,575
Total deferred tax assets	41,247	55,135
Less: valuation allowance	$ (41,247)	$ (55,135)

Income Taxes - Schedule of Reco

Income Taxes - Schedule of Reconciliation of Uncertain Tax Position (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Balance as of the beginning of the year	$ 1,283	$ 1,186
Increases related to tax positions in prior period	5	16
Increases related to tax positions taken during the current period	74	81
Balance at the end of the year	$ 1,362	$ 1,283

Geographic Information - Schedu

Geographic Information - Schedule of Revenue by Geographic Area (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues From External Customers And Long Lived Assets [Line Items]
Total revenue	$ 5,856	$ 4,177	$ 5,789	$ 5,475	$ 5,178	$ 3,676	$ 3,559	$ 3,187	$ 21,297	$ 15,600	$ 17,230
United States
Revenues From External Customers And Long Lived Assets [Line Items]
Total revenue									8,919	6,736	8,252
Europe and Middle East
Revenues From External Customers And Long Lived Assets [Line Items]
Total revenue									5,784	3,112	2,940
Asia Pacific
Revenues From External Customers And Long Lived Assets [Line Items]
Total revenue									4,353	3,552	2,989
Rest of World
Revenues From External Customers And Long Lived Assets [Line Items]
Total revenue									$ 2,241	$ 2,200	$ 3,049

Selected Quarterly Financial 71

Selected Quarterly Financial Data - Additional Information (Details)	Sep. 15, 2017
Quarterly Financial Data [Abstract]
Reverse stock split	1-for-10 reverse stock split
Reverse stock split, ratio	0.1

Selected Quarterly Financial 72

Selected Quarterly Financial Data (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Quarterly Financial Data [Abstract]
Total revenue	$ 5,856	$ 4,177	$ 5,789	$ 5,475	$ 5,178	$ 3,676	$ 3,559	$ 3,187	$ 21,297	$ 15,600	$ 17,230
Gross profit	2,759	1,703	2,302	2,383	2,014	1,272	1,104	779	9,147	5,169	4,717
Net loss	$ (1,064)	$ (6,596)	$ (5,007)	$ (5,175)	$ (4,932)	$ (5,928)	$ (5,172)	$ (5,814)	$ (17,842)	$ (21,846)	$ (22,971)
Basic and diluted net loss per share	$ (0.04)	$ (4.07)	$ (3.09)	$ (3.20)	$ (3.06)	$ (3.67)	$ (3.21)	$ (3.61)	$ (2.42)	$ (13.54)	$ (14.70)

Related Party Transactions - Ad

Related Party Transactions - Additional Information (Details) - Member of Board of Directors - Commercial Transaction - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Related Party Transaction [Line Items]
Aggregate revenue	$ 83,000	$ 240,000
Accounts receivable due from related party	$ 0	$ 0