iRhythm (IRTC) 10-Q 14 Nov 17 2017 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2017	Oct. 31, 2017
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	Q3
Trading Symbol	IRTC
Entity Registrant Name	iRhythm Technologies, Inc.
Entity Central Index Key	1,388,658
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding		22,981,467

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 20,429	$ 51,643
Investments, short-term	87,017	54,407
Accounts receivable, net	12,039	9,406
Inventory	1,314	1,390
Prepaid expenses and other current assets	1,989	1,671
Restricted cash		91
Total current assets	122,788	118,608
Investments, long-term		10,981
Property and equipment, net	6,207	4,653
Goodwill	862	862
Other assets	3,798	3,052
Total assets	133,655	138,156
Current liabilities:
Accounts payable	2,076	2,103
Accrued liabilities	11,436	10,165
Deferred revenue	904	947
Accrued interest, current portion	149
Debt, current portion	1,479
Total current liabilities	16,044	13,215
Debt	32,053	32,227
Deferred rent, noncurrent portion	169	26
Accrued interest, net of current portion		126
Total liabilities	48,266	45,594
Commitments and contingencies (Note 7)
Stockholders’ equity:
Preferred stock, $0.001 par value – 5,000,000 authorized at September 30, 2017 and December 31, 2016, respectively; and none issued and outstanding at September 30, 2017 and December 31, 2016, respectively
Common stock, $0.001 par value – 100,000,000 shares authorized at September 30, 2017 and December 31, 2016, respectively; 22,978,954 and 22,139,346 shares issued and outstanding at September 30, 2017 and December 31, 2016, respectively	28	22
Additional paid-in capital	230,831	219,718
Accumulated other comprehensive loss	(30)	(9)
Accumulated deficit	(145,440)	(127,169)
Total stockholders’ equity	85,389	92,562
Total liabilities and stockholders’ equity	$ 133,655	$ 138,156

Condensed Consolidated Balance3

Condensed Consolidated Balance Sheets (Parenthetical) (Unaudited) - $ / shares	Sep. 30, 2017	Dec. 31, 2016
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares issued	22,978,954	22,139,346
Common stock, shares outstanding	22,978,954	22,139,346

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Income Statement [Abstract]
Revenue	$ 25,035	$ 16,780	$ 70,327	$ 45,368
Cost of revenue	6,920	5,282	20,002	15,097
Gross profit	18,115	11,498	50,325	30,271
Operating expenses:
Research and development	3,790	1,635	9,187	4,847
Selling, general and administrative	20,308	12,529	57,787	36,658
Total operating expenses	24,098	14,164	66,974	41,505
Loss from operations	(5,983)	(2,666)	(16,649)	(11,234)
Interest expense	(862)	(807)	(2,522)	(2,388)
Other income (expense), net	321	(602)	900	(1,015)
Net loss	$ (6,524)	$ (4,075)	$ (18,271)	$ (14,637)
Net loss per common share, basic and diluted	$ (0.29)	$ (2.80)	$ (0.81)	$ (10.20)
Weighted-average shares used to compute net loss per common share, basic and diluted	22,811,907	1,454,307	22,446,399	1,434,583

Condensed Consolidated Stateme5

Condensed Consolidated Statements of Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Statement Of Income And Comprehensive Income [Abstract]
Net Loss	$ (6,524)	$ (4,075)	$ (18,271)	$ (14,637)
Other comprehensive loss:
Change in unrealized loss on available-for-sale securities	21		(19)
Comprehensive loss	$ (6,503)	$ (4,075)	$ (18,290)	$ (14,637)

Condensed Consolidated Stateme6

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Cash flows from operating activities
Net Loss	$ (18,271)	$ (14,637)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	1,103	646
Stock-based compensation	7,024	1,251
Amortization of debt discount and issuance costs	197	284
Amortization of premiums (accretion of discounts) on investments, net	(207)
Non-cash interest expense	1,152	1,099
Provision for bad debt and contractual allowance	5,927	3,384
Change in fair value of preferred stock warrant liabilities		996
Changes in operating assets and liabilities:
Accounts receivable	(8,560)	(7,115)
Inventory	76	(527)
Prepaid expenses and other current assets	(197)	(301)
Other assets	(793)	(842)
Accounts payable	(33)	69
Accrued liabilities	1,294	(363)
Deferred revenue	(43)	344
Deferred rent	143	(1)
Net cash used in operating activities	(11,188)	(15,713)
Cash flows from investing activities
Change in restricted cash	91
Purchases of property and equipment	(2,651)	(1,821)
Purchases of available-for-sale investments	(90,243)
Maturities of available-for-sale investments	68,682
Net cash used in investing activities	(24,121)	(1,821)
Cash flows from financing activities
Net proceeds from employee stock transactions	4,095	82
Payments of deferred issuance costs		(1,995)
Net cash provided by (used in) financing activities	4,095	(1,913)
Net decrease in cash and cash equivalents	(31,214)	(19,447)
Cash and cash equivalents, beginning of period	51,643	25,208
Cash and cash equivalents, end of period	20,429	5,761
Supplemental disclosures of cash flow information
Interest paid	1,152	1,213
Non-cash investing and financing activities
Deferred offering costs included in accounts payable and accrued liabilities		637
Property, plant and equipment costs included in accounts payable	$ 6	$ 152

Organization and Description of

Organization and Description of Business	9 Months Ended
	Sep. 30, 2017
Accounting Policies [Abstract]
Organization and Description of Business	1. Organization and Description of Business iRhythm Technologies, Inc. (the “Company”) was incorporated in the state of Delaware in September 2006. The Company is a digital healthcare company redefining the way cardiac arrhythmias are clinically diagnosed by combining wearable biosensing technology with cloud-based data analytics and machine-learning capabilities. The Company commenced commercial introduction of its products in the United States in 2009 following clearance by the U.S. Food and Drug Administration. The Company’s headquarters are based in San Francisco, California, and the Company has manufacturing facilities in Cypress, California, and clinical centers in Lincolnshire, Illinois and Houston, Texas. In March 2016, the Company formed a wholly-owned subsidiary in the United Kingdom. The Company manages its operations as a single operating segment. Substantially all of the Company’s assets are maintained in the United States. The Company derives substantially all of its revenue from sales to customers in the United States, based upon the billing address of the customer.

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2017
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation The accompanying financial statements have been prepared in accordance with generally accepted accounting principles in the United States of America, or U.S. GAAP, and applicable rules and regulations of the Securities and Exchange Commission, or SEC, regarding interim financial reporting. As permitted under those rules, certain footnotes or other financial information that are normally required by GAAP have been condensed or omitted, and accordingly the balance sheet as of December 31, 2016 has been derived from the audited consolidated financial statements at that date but does not include all of the information required by GAAP for complete consolidated financial statements. These unaudited condensed consolidated financial statements have been prepared on the same basis as the Company’s annual consolidated financial statements and, in the opinion of management, reflect all adjustments (consisting only of normal recurring adjustments) that are necessary for the fair statement of the Company’s condensed consolidated financial information. The results of operations for the three and nine months ended September 30, 2017 are not necessarily indicative of the results to be expected for the year ending December 31, 2017 or for any other interim period or for any other future year. The accompanying interim unaudited condensed consolidated financial statements and related financial information should be read in conjunction with the audited financial statements and the related notes thereto for the year ended December 31, 2016 included in the Company’s Form 10-K, filed with the SEC on March 31, 2017. Principles of Consolidation The accompanying interim unaudited condensed consolidated financial statements are consolidated for the nine months ended September 30, 2017 and 2016 and include the accounts of iRhythm Technologies, Inc. and its wholly-owned subsidiary, iRhythm Technologies Ltd., established in March 2016. The financial statements of iRhythm Technologies Ltd. use the U.S. dollar as the functional currency . For all non-functional currency balances, the remeasurement of such balances to functional currency results in a foreign exchange transaction gain or loss, which is recorded in the consolidated statements of operations. Use of Estimates The preparation of the condensed 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 financial statements and the reported amounts of revenues and expenses during the reporting period. On an ongoing basis, management evaluates its estimates, including those related to revenue recognition, contractual allowances for revenue, allowance for doubtful accounts, the useful lives of property and equipment, the recoverability of long-lived assets including the estimated usage of the printed circuit board assemblies (“PCBAs”), the valuation of deferred tax assets, the fair value of the Company’s preferred and common stock and stock-based compensation. The Company bases these estimates on historical and anticipated results, trends, and various other assumptions that the Company believes are reasonable under the circumstances, including assumptions as to future events. Actual results may differ from those estimates. Fair Value of Financial Instruments The carrying amounts of certain of the Company’s financial instruments, which include cash equivalents, short-term investments, accounts receivable, accounts payable and accrued liabilities, approximate fair value due to their short maturities. Cash Equivalents Cash equivalents consist of short-term, highly liquid investments with original maturities of three months or less from the date of purchase. Investments Short-term investments consist of debt securities classified as available-for-sale and have maturities greater than 90 days, but less than 365 days from the date of acquisition. Long-term investments have maturities greater than 365 days as of the balance sheet date. All investments are carried at fair value based upon quoted market prices. Unrealized gains and losses on available-for-sale securities are excluded from earnings and are reported as a component of accumulated other comprehensive loss. The cost of available-for-sale securities sold is based on the specific-identification method. Realized gains and losses are included in earnings, and are derived for specific-identification method for determining the costs of investments sold. Restricted Cash Restricted cash consists of certificates of deposit held with a financial institution as security deposits for building leases and is included in short-term assets on the Company's condensed consolidated balance sheets. Accounts Receivable, Allowance for Doubtful Accounts and Contractual Allowance Accounts receivable consists of amounts due to the Company from institutions, government payors and third-party commercial payors as a result of the Company's normal business activities. Accounts receivable is reported on the condensed consolidated balance sheets net of an estimated allowance for doubtful accounts and contractual allowance. The Company establishes an allowance for doubtful accounts for estimated uncollectible receivables based on its historical experience, and recognizes the provision as a component of selling, general and administrative expenses. The Company establishes a contractual allowance, which is a reduction in revenue, for estimated uncollectible amounts from Centers for Medicare & Medicaid Services (“CMS”) and contracted third-party commercial payors. The following table presents the changes in the allowance for doubtful accounts: September 30, December 31, 2017 2016 Balance, beginning of period $ 1,792 $ 1,125 Add: provision for doubtful accounts 1,855 1,960 Less: write-offs, net of recoveries and other adjustments (852 ) (1,293 ) Balance, end of period $ 2,795 $ 1,792 The following table presents the changes in the contractual allowance: September 30, December 31, 2017 2016 Balance, beginning of period $ 2,340 $ 338 Add: contractual allowances 4,072 2,726 Less: write-offs, net of recoveries and other adjustments (678 ) (724 ) Balance, end of period $ 5,734 $ 2,340 Management reviews and updates its estimates for the allowances for doubtful accounts and contractual allowance periodically to reflect its experience regarding historical collections. If management were to make different judgments or utilize different estimates in the allowances for doubtful accounts and contractual allowance, differences in the amount of reported selling, general and administrative expenses and revenue could result, respectively. Concentrations of Risk Credit Risk Financial instruments that potentially subject the Company to a concentration of credit risk consist primarily of cash and cash equivalents, investments and accounts receivable. Cash, cash equivalents, and investments are deposited in financial institutions which, at times, may be in excess of federally insured limits. Cash equivalents are invested in highly rated money market funds. The Company invests in a variety of financial instruments, such as, but not limited to, United States Government securities, corporate notes, commercial paper and, by policy, limits the amount of credit exposure with any one financial institution or commercial issuer. The Company has not experienced any material losses on its deposits of cash and cash equivalents or investments. Concentrations of credit risk with respect to accounts receivable are limited due to the large number of customers comprising the Company’s customer base and their dispersion across many geographies. The Company does not require collateral. The Company records an allowance for doubtful accounts when it becomes probable that a receivable will not be collected. Government agencies, including CMS and the Veterans Administration, accounted for approximately 39%, 38%, 38% and 40% of the Company’s revenue for the three and nine months ended September 30, 2017 and 2016 respectively. Accounts receivable related to government agencies accounted for 26% and 27% at September 30, 2017 and December 31, 2016, respectively. Supply Risk While the Company has not experienced manufacturing supply disruptions to date, the Company relies on single-source vendors for the supply of its disposable housings, instruments and other materials used to manufacture the ZIO Patch and the adhesive that binds the ZIO Patch to a patient’s body. These components and materials are critical, and there could be a considerable delay in finding alternative sources of supply. Inventory Inventory is stated at the lower of cost or net realizable value, cost being determined on a standard cost basis for material costs and on actual cost basis for labor and overhead, which approximates actual cost on a first in, first out (“FIFO)” basis, and market being determined as the lower of cost or net realizable value. The Company records write-downs of inventory that is obsolete or in excess of anticipated demand or market value based on consideration of product lifecycle stage, technology trends, product development plans and assumptions about future demand and market conditions. Actual demand may differ from forecasted demand and such differences may have a material effect on recorded inventory values. Inventory write-downs are charged to cost of revenue and establish a new cost basis for the inventory. Property and Equipment Property and equipment are stated at cost less accumulated depreciation and amortization. Depreciation and amortization is computed using the straight-line method over the estimated useful lives of the assets, ranging from three to five years. Leasehold improvements are amortized over the shorter of the lease term or the estimated useful lives of the assets. Maintenance and repairs are charged to expense as incurred and improvements and betterments are capitalized. Internal-Use Software The Company capitalizes costs related to internal-use software during the application development stage. Costs related to planning and post implementation activities are expensed as incurred. Capitalized internal-use software is amortized, and recognized as cost of revenue, on a straight-line basis over the estimated useful life, which is up to five years. The Company evaluates the useful lives of these assets on an annual basis and tests for impairment whenever events or changes in circumstances occur that could impact the recoverability of these assets. Capitalized internal-use software costs are classified as a component of property and equipment. Goodwill Goodwill represents the excess of the purchase price paid over the fair value of tangible and identifiable intangible net assets acquired in business combinations. Goodwill is tested for impairment on an annual basis and at any other time if events occur or circumstances indicate that the carrying amount of goodwill may not be recoverable. Such events or circumstances may include significant adverse changes in the general business climate, among other things. The impairment test is performed by determining the enterprise fair value of the Company, which is primarily based on the Company’s market capitalization. If the Company’s carrying value, as a one reporting unit entity, is less than its fair value, then the fair value is allocated to all of its assets and liabilities (including any unrecognized intangible assets) as if the fair value was the purchase price to acquire the Company. The excess of the fair value over the amounts assigned to the Company’s assets and liabilities is the implied fair value of the goodwill. If the carrying amount of goodwill exceeds the implied fair value of that goodwill, an impairment loss is recognized in an amount equal to that excess. The Company performs its annual evaluation of goodwill during the fourth quarter of each fiscal year. The Company did not record any charges related to goodwill impairment in any of the periods presented in these condensed consolidated financial statements. Impairment of Long-Lived Assets The Company annually reviews long-lived assets 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 cash flows which the assets are expected to generate. If such assets are considered to be impaired, the impairment to be recognized is measured as the amount by which the carrying amount of the assets exceeds the projected discounted future net cash flows arising from the asset. To date there have been no such impairments of long-lived assets. Other Assets Included in the other assets are PCBAs totaling $3.5 million and $2.8 million as of September 30, 2017 and December 31, 2016, respectively. The Company uses a PCBA in each wearable device and it is used numerous times and has a useful life beyond one year. Each time the PCBA is used in a wearable device, a portion of the cost of the PCBA is recorded as a cost of revenue. The Company has based its estimates of how many times a PCBA can be used on testing in research and development, loss rates, product obsolescence, and the amount of time it takes the device to go through the manufacturing, shipping, customer shelf and patient wear time and upload process. The Company periodically evaluates the use estimate. Comprehensive Loss Comprehensive loss represents all changes in stockholders' equity except those resulting from and distributions to stockholders. The Company’s unrealized gains and losses on available-for-sale securities represent the only component of other comprehensive loss that are excluded from the reported net loss and that are presented in the condensed consolidated statements of comprehensive loss. Revenue Recognition The Company’s devices, cardiac rhythm monitors, have a wear period for up to 14 days for the ZIO Service or 30 days for the ZIO Event Card. The Company's services, consisting of the delivery of reports containing analysis of data captured by the physical device to the prescribing physician, are generally billable at the start of the wear period or when reports are issued to physicians, depending on the service provided. For the ZIO Event Card, the Company recognizes revenue on a straight-line basis over the applicable wear period, as the event monitoring results are delivered to physicians. For the ZIO Service, the Company recognizes the revenue at the time that a report is delivered to a physician. For all services performed, the Company considers whether or not the following revenue recognition criteria are met: persuasive evidence of an arrangement exists and delivery has occurred or services have been rendered. For services performed for customers the Company invoices directly, additional revenue recognition criteria include that the price is fixed and determinable and collectability is reasonably assured; for customers in which the Company submits claims to third-party commercial and governmental payors for reimbursement, it recognizes revenue only when a reasonable estimate of reimbursement can be made. The assessment of whether a reasonable estimate of reimbursement can be made requires significant judgment by management. Where management's judgment indicates a reasonable estimate of reimbursement can be made, revenue is recognized upon delivery of the patient report for the ZIO Service and straight-line for the ZIO Event Card. Some patients have out-of-pocket costs for amounts not covered by their insurance carrier, and the Company may bill the patient directly for these amounts in the form of co-payments and co-insurance in accordance with their insurance carrier and health plans. Some payors may not cover the Company's service as ordered by the prescribing physician under their reimbursement policies. In the absence of an agreement with the patient or other clearly enforceable legal right to demand payment from the patient, the related revenue is recognized upon the earlier of notification of the payor benefits allowed or when payment is received, until the Company has the ability to make a reasonable estimate. Once a reasonable estimate can be made, revenue is recognized upon delivery of the service. During 2017, the Company recognized revenue from certain non-contracted payors as a reasonable estimate was able to be made, primarily based on the consistency of historical payments. The Company recognizes revenue related to billings for CMS and commercial payors on an accrual basis, net of contractual allowances, when a reasonable estimate of reimbursement can be made. These contractual allowances represent the difference between the list price (the billing rate) and the reimbursement rate for each payor. Upon ultimate collection from CMS and commercial payors, the amount is compared to the previous estimates and the contractual allowance is adjusted accordingly. Until a contract has been negotiated with a commercial payor, the Company’s services may or may not be covered by these entities' existing reimbursement policies. In addition, patients do not enter into direct agreements with the Company that commit them to pay any portion of the cost of the service in the event that their insurance declines to reimburse the Company. In the absence of an agreement with the patient or other clearly enforceable legal right to demand payment from the patient, the related revenue is recognized upon the earlier of notification of the payor benefits allowed or when payment is received, until the Company has the ability to make a reasonable estimate. Contracted revenue recognized on an accrual basis was $22.5 million, $13.3 million, $62.1 million and $37.6 million for the three and nine months ended September 30, 2017 and 2016, respectively. Revenue related to non-contracted claims was $2.5 million, $3.5 million, $8.2 million and $7.8 million for the three and nine months ended September 30, 2017 and 2016, respectively. Certain of the Company’s customers pay the Company directly for the ZIO Service upon shipment of devices. Such advance payments are recorded as deferred revenue on the condensed consolidated balance sheets and revenue is recognized when reports are delivered to physicians. Cost of Revenue Cost of revenue is expensed as incurred and includes direct labor, material costs, equipment and infrastructure expenses, amortization of internal-use software, allocated overhead, and shipping and handling. Material costs include both the disposable costs of the device and amortization of the PCBAs. Each time the PCBA is used in a wearable device, a portion of the cost of the PCBA is recorded as a cost of revenue. Research and Development The Company’s research and development costs are expensed as incurred. Research and development costs include, but are not limited to, payroll and personnel-related expenses, laboratory supplies, consulting costs and overhead charges. Income Taxes The Company uses the asset and liability method to account for income taxes in accordance with the authoritative guidance for income taxes. Under this method, deferred tax assets and liabilities are determined based on future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases, and tax loss and credit carryforwards. Deferred tax assets and liabilities are measured using enacted tax rates applied to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in income in the period that includes the enactment date. A valuation allowance is established when necessary to reduce deferred tax assets to the amount expected to be realized. The Company recognizes the effect of income tax positions only if those positions are more likely than not of being sustained. Recognized income tax positions are measured at the largest amount that is greater than 50% likely of being realized. Changes in recognition or measurement are reflected in the period in which the change in judgment occurs. The Company records interest and penalties related to unrecognized tax benefits in income tax expense. To date, there have been no interest or penalties charged in relation to the unrecognized tax benefits. Stock-based Compensation The Company measures its stock-based awards made to employees based on the estimated fair values of the awards as of the grant date. The fair value of stock options are determined using the Black-Scholes option pricing model. Stock-based compensation expense is recognized over the requisite service period using the straight-line method and is based on the value of the portion of stock-based payment awards that is ultimately expected to vest. As such, the Company’s stock-based compensation is reduced for the estimated forfeitures at the date of grant and revised, if necessary, in subsequent periods if actual forfeitures differ from those estimates. For restricted stock, the compensation cost for these awards is based on the closing price of the Company’s common stock on the date of grant, and recognized as compensation expense on a straight-line basis over the requisite service period. The Company recognizes compensation expense related to the Employee Stock Purchase Program (“ESPP”) based on the estimated fair value of the options on the date of grant, net of estimated forfeitures. The Company estimates the grant date fair value, and the resulting stock-based compensation expense, using the Black-Scholes option pricing model for each purchase period. The grant date fair value is expensed on a straight-line basis over the offering period. Net Loss per Common Share Basic net loss per common share is calculated by dividing the net loss by the weighted average number of shares of common stock outstanding during the period, without consideration of potentially dilutive securities. Diluted net loss per common share is the same as basic net loss per common share for all periods presented since the effect of potentially dilutive securities are anti-dilutive. Reclassification of Prior Year Presentation Certain prior year amounts have been reclassified for consistency with the current period presentation. These reclassifications had no effect on the Company’s results of operations, net loss or cash flows. Recent Accounting Pronouncements In May 2014, the Financial Accounting Standards Board (“FASB”), issued Accounting Standards Update (“ASU”) Revenue from Contracts with Customers (Topic 606) In addition, Topic 606 requires more detailed disclosures to enable users of financial statements to understand the nature, timing and uncertainty of revenue and cash flows arising from a review of historical accounting policies and practices to identify potential differences in applying Topic 606. The Company plans to adopt this standard on January 1, 2018 and will use the modified retrospective approach recognizing the cumulative effect of adopting this guidance as an adjustment to its opening accumulated deficit balance, which will have no effect on the Company’s consolidated statements of operations or cash flows for the quarter or year ended December 31, 2017. Prior periods will not be retrospectively adjusted. While the evaluation of the new standard is ongoing, the Company believes the adoption will result in a change to net revenue primarily due to the recognition of bad debt expense related to the patient responsibility of both contracted and non-contracted claims, which was $1.7 million for the nine months ended September 30, 2017, as a reduction of gross revenue rather than as a component of selling, general and administrative and, to a lesser extent, due to timing differences in its recognition of revenue related to non-contracted third-party payor claims as a result of changing from recognition based on the earlier of notification of the payor benefits allowed or when payment is received to the accrual basis based on historical experience. In March 2016, the FASB issued ASU No. 2016-09, Compensation—Stock Compensation (Topic 718) On May 10, 2017, the FASB issued ASU 2017-09, Scope of Modification Accounting The Company is currently evaluating the impact of this new guidance.

Cash Equivalents and Investment

Cash Equivalents and Investments	9 Months Ended
	Sep. 30, 2017
Cash And Cash Equivalents [Abstract]
Cash Equivalents and Investments	3. Cash Equivalents and Investments The fair value of securities, not including cash at September 30, 2017 and December 31, 2016, were as follows (in thousands): September 30, 2017 Amortized Gross Unrealized Estimated Cost Gains Losses Fair Value Money market funds $ 5,722 $ — $ — $ 5,722 U.S. government securities 35,942 1 (26 ) 35,917 Corporate notes 15,669 1 (4 ) 15,666 Commercial paper 48,130 — — 48,130 Total available-for-sale securities $ 105,463 $ 2 $ (30 ) $ 105,435 Classified as: Cash equivalents $ 18,418 Short-term investments 87,017 Total cash equivalents and investments $ 105,435 December 31, 2016 Amortized Gross Unrealized Estimated Cost Gains Losses Fair Value Money market funds $ 45,937 $ — $ — $ 45,937 U.S. government securities 16,479 11 — 16,490 Corporate notes 23,947 — (20 ) 23,927 Commercial paper 24,971 — — 24,971 Total available-for-sale securities $ 111,334 $ 11 $ (20 ) $ 111,325 Classified as: Cash equivalents $ 45,937 Short-term investments 54,407 Long-term investments 10,981 Total cash equivalents and investments $ 111,325 Available-for-sale securities held as of September 30, 2017 had a weighted average days to maturity of 122 days. There have been no material realized gains or realized losses on available-for-sale securities for the periods presented. As the carrying value approximates the fair value for the Company’s cash equivalents, short-term and long-term investments shown in the tables above, the following table summarizes the fair value of the Company’s cash equivalents, short-term and long-term investments classified by maturity (in thousands): September 30, December 31, 2017 2016 Due within one year $ 105,435 $ 100,344 Due after one year through three years — 10,981 Total available-for-sale marketable debt securities $ 105,435 $ 111,325

Fair Value Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2017
Fair Value Disclosures [Abstract]
Fair Value Measurements	4. Fair Value Measurements The Company discloses and recognizes the fair value of its assets and liabilities using a hierarchy that prioritizes the inputs to valuation techniques used to measure fair value. Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability (an exit price) in an orderly transaction between market participants at the reporting date. The hierarchy gives the highest priority to valuations based upon unadjusted quoted prices in active markets for identical assets or liabilities (Level 1 measurements) and the lowest priority to valuations based upon unobservable inputs that are significant to the valuation (Level 3 measurements). The guidance establishes three levels of the fair value hierarchy as follows: Level 1 - Inputs are unadjusted quoted prices in active markets for identical assets or liabilities at the measurement date. Level 2 - Inputs (other than quoted market prices included in Level 1) are either directly or indirectly observable for the asset or liability through correlation with market data at the measurement date and for the duration of the instrument’s anticipated life. Level 3 - Inputs reflect management’s best estimate of what market participants would use in pricing the asset or liability at the measurement date. Consideration is given to the risk inherent in the valuation technique and the risk inherent in the inputs to the model. Assets and liabilities measured at fair value are classified in their entirety based on the lowest level of input that is significant to the fair value measurement. The Company’s assessment of the significance of a particular input to the fair value measurement in its entirety requires management to make judgments and consider factors specific to the asset or liability. The corporate notes, commercial paper and government bonds are classified as Level 2 as they were valued based upon quoted market prices for similar instruments in active markets, quoted prices for identical or similar instruments in markets that are not active and model-based valuation techniques for which all significant inputs are observable in the market or can be corroborated by observable market data for substantially the full term of the assets. Based on Level 2 inputs and the borrowing rates currently available to the Company for loans with similar terms and maturities, the carrying value of the Company’s debt approximates its fair value. The following table presents the fair value of the Company’s financial assets and liabilities determined using the inputs defined above (amounts in thousands). September 30, 2017 Level 1 Level 2 Level 3 Total Assets Money market funds $ 5,722 $ — $ — $ 5,722 U.S. government securities — 35,917 — 35,917 Corporate notes — 15,666 — 15,666 Commercial paper — 48,130 — 48,130 Total $ 5,722 $ 99,713 $ — $ 105,435 December 31, 2016 Level 1 Level 2 Level 3 Total Assets Money market funds $ 45,937 $ — $ — $ 45,937 U.S. government securities — 16,490 — 16,490 Corporate notes — 23,927 — 23,927 Commercial paper — 24,971 — 24,971 Total $ 45,937 $ 65,388 $ — $ 111,325 The following table sets forth a summary of the changes in the fair value of the preferred stock warrants which is classified as Level 3 in the fair value hierarchy. There were no transfers into or out of Level 3 during the periods (in thousands): Nine Months Ended September 30, 2017 Nine Months Ended September 30, 2016 Beginning balance $ — $ 2,949 Total change in fair value recorded as other expense, net — 996 Ending balance $ — $ 3,945 The valuation of the preferred stock warrant liabilities is discussed in Note 11.

Balance Sheet Components

Balance Sheet Components	9 Months Ended
	Sep. 30, 2017
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Balance Sheet Components	5. Balance Sheet Components Inventory and PCBAs Inventory and PCBAs consisted of the following (in thousands): September 30, 2017 December 31, 2016 Raw materials $ 737 $ 839 Finished goods 4,119 3,324 Total $ 4,856 $ 4,163 Reported on the consolidated balance sheet as: Inventory $ 1,314 $ 1,390 Other assets 3,542 2,773 Total $ 4,856 $ 4,163 Amounts reported as other assets are comprised of the PCBA costs that are included in both raw materials and finished goods totals above. Property and Equipment, Net Property and equipment, net consisted of the following (in thousands): September 30, December 31, 2017 2016 Laboratory and manufacturing equipment $ 2,028 $ 1,509 Computer equipment and software 916 736 Furniture and fixtures 928 657 Leasehold improvements 703 502 Internal-use software 4,387 2,900 Total property and equipment, gross 8,962 6,304 Less: accumulated depreciation and amortization (2,755 ) (1,651 ) Total property and equipment, net $ 6,207 $ 4,653 Depreciation and amortization expense for the three and nine months ended September 30, 2017 and 2016 was $0.5 million, $0.2 million, $1.1 million and $0.6 million, Accrued Liabilities Accrued liabilities consisted of the following (in thousands): September 30, December 31, 2017 2016 Accrued vacation $ 1,923 $ 1,642 Accrued payroll and related expenses 5,627 6,179 Accrued ESPP contributions 1,029 417 Accrued professional services fees 555 636 Other 2,302 1,291 Total accrued liabilities $ 11,436 $ 10,165

Related-Party Transactions

Related-Party Transactions	9 Months Ended
	Sep. 30, 2017
Related Party Transactions [Abstract]
Related-Party Transactions	6. Related-Party Transactions Kaiser Permanente (“Kaiser”) is a common stockholder of the Company, representing 6.1% ownership of the total outstanding shares of the Company as of December 31, 2016. For the three and nine months ended September 30, 2017 and 2016, the Company recognized revenue of $1.0 million, $0.4 million, $2.8 million and $1.8 million, respectively, for transactions with Kaiser. The amounts receivable from transactions with Kaiser were $0.7 million and $0.4 million as of September 30, 2017 and December 31, 2016, respectively. Kaiser performs services related to clinical trials and the Company utilizes Kaiser for employee healthcare and the total expense recorded was $0.3 million, $0.1 million, $0.5 million, and $0.5 million as of the three and nine months ended September 30, 2017 and 2016, respectively. The amounts outstanding and included in accounts payable and accrued liabilities were $0.3 million and $0.2 million as of September 30, 2017, and December 31, 2016 respectively.

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2017
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	7. Commitments and Contingencies Lease Arrangements The Company leases office and manufacturing space under non-cancelable operating leases which expire on various dates through 2027. These leases generally contain scheduled rent increases or escalation clauses and renewal options. The Company recognizes rent expense on a straight-line basis over the lease period. I n May 2017, the Company entered into a commercial building lease agreement for its clinical center in Houston, Texas which expires in September 2027. The following table summarizes the Company’s future minimum lease payments as of September 30, 2017 (in thousands): Period Ending December 31: 2017 (remainder of year) $ 1,263 2018 5,089 2019 5,108 2020 1,178 2021 406 Thereafter 2,541 Total $ 15,585 The Company’s rent expense was $1.3 million, $0.6 million, $3.8 million and $1.6 million for the three and nine months ended September 30, 2017 and 2016, respectively. Legal Proceedings From time to time, the Company may become involved in legal proceedings arising from the ordinary course of its business. Management is currently not aware of any matters that could have a material adverse effect on the financial position, results of operations or cash flows of the Company. Indemnifications In the ordinary course of business, the Company enters into agreements that may include indemnification provisions. Pursuant to such agreements, the Company may indemnify, hold harmless and defend an indemnified party for losses suffered or incurred by the indemnified party. Some of the provisions will limit losses to those arising from third-party actions. In some cases, the indemnification will continue after the termination of the agreement. The maximum potential amount of future payments the Company could be required to make under these provisions is not determinable. The Company has also entered into indemnification agreements with its directors and officers that may require the Company to indemnify its directors and officers against liabilities that may arise by reason of their status or service as directors or officers to the fullest extent permitted by California corporate law. The Company currently has directors’ and officers’ insurance. The Company has never incurred material costs to defend lawsuits or settle claims related to these indemnification provisions, and believes that the estimated fair value of these indemnification obligations is not material and it has not accrued any amounts for these obligations.

Debt

Debt	9 Months Ended
	Sep. 30, 2017
Debt Disclosure [Abstract]
Debt	8. Debt Pharmakon Loan Agreement In December 2015, the Company entered into the Loan Agreement with Biopharma Secured Investments III Holdings Cayman LP, or Pharmakon (the “Pharmakon Loan Agreement”). The Pharmakon Loan Agreement provides for up to $55.0 million in term loans split into two tranches as follows: (i) the Tranche A Loans are $30.0 million in term loans, and (ii) the Tranche B Loans are up to $25.0 million in term loans. The Tranche A Loans were drawn on December 4, 2015. The Tranche B Loans were available to be drawn prior to December 4, 2016. No additional draw was made. During the first full eight quarters, payments are interest only and for the first two years, 50% of the interest will be “paid-in-kind.” The Company is subject to a financial covenant related to minimum trailing revenue targets that begins in June 2017, and is tested on a semi-annual basis. The minimum net revenue covenant ranges from $44.7 million for the period ended June 30, 2017 to $102.6 million for the period ended December 31, 2021. To date all minimum revenue targets have been achieved. The minimum net revenues financial covenant has a 45-day equity cure period following required delivery date of the financial statements. Pursuant to this equity cure provision, the Company may cure a revenue covenant default by raising additional funds from the sale of equity. The Company was in compliance with loan covenants as of September 30, 2017. The loan matures December 2021. The Tranche A Loans bear interest at a fixed rate equal to 9.50% per annum that is due and payable quarterly in arrears. During the first eight calendar quarters, 50% of the interest due and payable shall be added to the then outstanding principal. The Pharmakon Loan Agreement requires the Company to maintain a minimum consolidated liquidity and minimum net revenue during the term of the loan facility and contains customary affirmative and negative covenants and event of default provisions that could result in the acceleration of the repayment obligations under the loan facility. Upon a change in control of the Company, Pharmakon has the option to demand payment in full of the outstanding loans together with any prepayment premium. The obligations under the Pharmakon Loan Agreement are secured by a security interest in substantially all of the Company’s assets pursuant to the Pharmakon Guaranty and Security Agreement and this security interest is governed by an intercreditor agreement between Pharmakon and Silicon Valley Bank (“SVB”). In December 2015, the Company used the proceeds from the Pharmakon Loan Agreement to repay $4.9 million of bank debt to SVB. The issuance costs and debt discount have been netted against the borrowed funds on the balance sheet. The debt balance as of September 30, 2017 and December 31, 2016 was $32.1 million and $30.8 million, respectively. Bank Debt In June 2014, the Company refinanced its debt with SVB by entering into the Second Amendment to the Amended and Restated Loan Security Agreement (“Second Amendment”). Under this amendment, the Company borrowed $4.9 million with an additional advance of $5.0 million available. All the borrowings under the Second Amended Loan Agreement were collateralized by all of the Company’s assets, excluding intellectual property. In connection with entering into the Amended Loan Agreement, the Company issued warrants to purchase 20,136 shares of Series D at $7.31 per share that expire in June 2024 (See Note 11). In December 2015, the Company used the proceeds from the Pharmakon Loan Agreement to repay $4.9 million of bank debt to SVB and entered into a Second Amended and Restated Loan and Security Agreement with SVB, or the SVB Loan Agreement. Under the SVB Loan Agreement the Company may borrow, repay and reborrow under a revolving credit line, but not in excess of the maximum loan amount of $15.0 million, until December 4, 2018, when all outstanding principal and accrued interest becomes due and payable. Any principal amount outstanding under the SVB revolving credit line shall bear interest at a floating rate per annum equal to the rate published by The Wall Street Journal as the “Prime Rate” plus 0.25%, are tied to the Company’s trailing six-month revenue and subject to certain revenue targets. The Company may borrow up to 80% of its eligible accounts receivable, up to the maximum of $15.0 million. In August 2016, the Company obtained a $3.1 million standby letter of credit pursuant to the SVB revolving credit facility in connection with a lease for the San Francisco office. As of September 30, 2017 and December 31, 2016, the Company was eligible to borrow up to $7.7 million and $2.5 million, respectively, under the SVB revolving credit line. The SVB Loan Agreement requires the Company to maintain a minimum consolidated liquidity and minimum net sales during the term of the loan facility. In addition, the SVB Loan Agreement contains customary affirmative and negative covenants and events of default. The Company was in compliance with loan covenants as of September 30, 2017. The obligations under the SVB Loan Agreement are collaterialized by substantially all assets of the Company and this security interest is governed by an intercreditor agreement between Pharmakon and SVB. California HealthCare Foundation Note In November 2012, the Company entered into a Note Purchase Agreement and Promissory Note with the California HealthCare Foundation, or the CHCF Note, through which the Company borrowed $1.5 million. The CHCF Note accrues simple interest of 2.0%. The accrued interest and the principal was to mature in November 2016. In partial consideration for the issuance of the CHCF Note, the Company issued warrants to purchase 22,807 shares of the Company’s Series D convertible preferred stock. In June 2015, the Company amended the CHCF Note to extend the maturity date to May 2018. In partial consideration for the amendment, the Company issued 8,552 warrants at $6.58 exercise price per share of the Company’s Series D convertible preferred stock. The CHCF note is subordinate to other debt. The debt balance, net of debt discount, as of September 30, 2017 and December 31, 2016 was $1.6 million and $1.5 million, respectively.

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2017
Income Tax Disclosure [Abstract]
Income Taxes	9. Income Taxes The Company did not record a provision or benefit for income taxes during the three and nine months ended September 30, 2017 and 2016, respectively, as it reported losses in each period which are not more likely than not to be realized. Due to the uncertainties surrounding the realization of deferred tax assets through future taxable income, the Company has provided a full valuation allowance and, therefore, no benefit has been recognized for the net operating loss carryforwards and other deferred tax assets. At December 31, 2016, the Company had $0.6 million of unrecognized tax benefit, none of which, if recognized, would affect the effective tax rate as most of the unrecognized tax benefit is deferred tax assets currently offset by a valuation allowance. A number of years may elapse before an uncertain tax position is audited and finally resolved. While it is often difficult to predict the final outcome or the timing of resolution of any particular uncertain tax position, the Company believes that its reserves for income taxes reflect the most likely outcome. The Company adjusts these reserves in light of changing facts and circumstances. Settlement of any particular position could require the use of cash. As of September 30, 2017, changes to the Company’s uncertain tax positions in the next twelve months that are reasonably probable are not expected to have a material impact on the Company’s financial position or results of operations.

Stockholders' Equity

Stockholders' Equity	9 Months Ended
	Sep. 30, 2017
Equity [Abstract]
Stockholders' Equity	10. Stockholders’ Equity Common stock As of September 30, 2017, the Company’s amended and restated certificate of incorporation dated October 2016, authorized the Company to issue 100,000,000 shares of common stock with a par value of $0.001 per share and 5,000,000 shares of preferred stock with a par value of $0.001 per share. The holders of common stock are entitled to receive dividends whenever funds and assets are legally available and when declared by the board of directors. No dividends were declared through September 30, 2017. The Company had reserved shares of common stock for issuance as follows: September 30, December 31, 2017 2016 Options issued and outstanding 2,765,902 2,977,218 Unvested restricted stock units 453,063 105,529 Common stock warrants issued and outstanding 127,918 217,245 Shares available for grant under future stock plans 4,774,565 4,226,068 8,121,448 7,526,060

Preferred Stock Warrant Liabili

Preferred Stock Warrant Liabilities	9 Months Ended
	Sep. 30, 2017
Preferred Stock Warrant Liabilities [Abstract]
Preferred Stock Warrant Liabilities	11. Preferred Stock Warrant Liabilities In November 2012, in connection with borrowings under a convertible note, the Company issued warrants to purchase shares of Series C or New Preferred. The warrants were only exercisable if the Convertible Notes were converted into Series C or New Preferred. The warrants’ exercise price is $0.001 per share and they have a seven year term. On March 27, 2013 the Company closed the Series D financing. The warrants were converted into warrants to purchase 207,177 shares of Series D convertible preferred stock. The Company recognized a charge of $0.5 million and $0.7 million related to the change in the fair value of the warrants for the three and nine months ended September 30, 2016. Upon the IPO, the Series D preferred stock warrants converted into common stock warrants and were reclassified to additional paid-in-capital in the Company's balance sheet. As a result, the warrants are no longer subject to fair value remeasurement. As of September 30, 2017, 127,918 warrants were outstanding. In June 2014, in connection with borrowings under the Second Amendment (Note 8), the Company issued warrants to purchase 20,136 shares of Series D Preferred Stock at $7.31 per share that expire June 2024. The fair value of the warrants was determined by using an option pricing model prepared by a third-party based on an allocation of the Company’s aggregate value to the outstanding equity instruments, applying a 30% discount to the warrant value for lack of marketability. The fair value of the warrant, $0.1 million, was recorded as a debt discount and is being amortized over the loan repayment period to interest expense. The Company recognized a charge of $15,000 and income of $41,000 related to change in the fair value of the warrants for the three and nine months ended September 30, 2016. The warrants were converted into warrants to purchase common stock upon the completion of the IPO in 2016, and were reclassified to additional paid-in-capital in the Company's balance sheet. One of the warrants for 10,068 shares was exercised through a cashless exercise on October 26, 2016 resulting in the issuance of a net 7,310 shares of the Company's common stock, and the other warrant for 10,068 was exercised through a cashless exercise on May 2, 2017 resulting in the issuance of a net 8,077 shares.

Stock Incentive Plans

Stock Incentive Plans	9 Months Ended
	Sep. 30, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock Incentive Plans	12. Stock Incentive Plans 2006 Plan In October 2006, the Company adopted the 2006 Equity Incentive Plan, as amended, (the “2006 Plan”). The Plan provided for the granting of stock options to employees and non-employees of the Company. Options granted under the Plan were either incentive stock options or nonqualified stock options. Incentive stock options (“ISO”) were granted only to employees (including officers and directors who are also employees). Nonqualified stock options (“NSO”) were granted to employees and non-employees. The board of directors had the authority to determine to whom options will be granted, the number of options, the term and the exercise price. Options under the Plan were granted for periods of up to ten years and at the fair value of the shares on the date of grant as determined by the board of directors. In general, options were exercisable at a rate of 25% after the first anniversary of the grant and then monthly vesting for an additional three years from date of grant. The term for options is no longer than five years for ISOs for which the grantee owns greater than 10% of the voting power of all classes of stock and no longer than ten years for all other options. The Company issues new shares upon the exercise of options. 2016 Plan In October 2016, the Company adopted the 2016 Equity Incentive Plan, (the “2016 Plan”). The 2016 Plan was subsequently approved by the Company’s stockholders and became effective on October 19, 2016, immediately before the effective date of the IPO. Following the effectiveness of the 2016 Plan, no additional options were granted under the 2006 Plan. In addition, to the extent that any awards outstanding or subject to vesting restrictions under the 2006 Plan are subsequently forfeited or terminated for any reason before being exercised or settled, the shares of common stock reserved for issuance pursuant to such awards as of the closing of the IPO will become available for issuance under the 2016 Plan. The remaining shares available for grant under the 2006 Plan became available for issuance under the 2016 Plan upon the closing of the IPO. On the first day of each year beginning with 2017, the 2016 Plan authorizes an annual increase of the least of 3,865,000 shares, 5% of outstanding common stock on the last day of the immediately preceding fiscal ye ar or an amount as determined by the Company's Board of Directors. As of September 30, 2017, the Company has reserved 4,971,966 shares of common stock for issuance under the 2016 Stock Incentive Plan. Pursuant to the 2016 Plan, stock options, restricted shares, stock units, including restricted stock units and stock appreciation rights, may be granted to employees, consultants, and outside directors of the Company. Options granted may be either ISOs or NSOs. Stock options are governed by stock option agreements between the Company and recipients of stock options. ISOs and NSOs may be granted under the 2016 Plan at an exercise price of not less than 100% of the fair market value of the common stock on the date of grant, determined by the Compensation Committee of the Board of Directors. Options become exercisable and expire as determined by the Compensation Committee, provided that the term of ISOs may not exceed ten years from the date of grant. Employee Stock Purchase Program (“ESPP”) In October 2016, the Company’s Board of Directors and stockholders approved the Employee Stock Purchase Plan (the “ESPP”). Under the ESPP, the Company initially reserved 483,031 shares of common stock for issuance as of its effective date of October 19, 2016. On the first day of each calendar year, beginning in 2017, the number of shares in the reserve will increase by the lesser of 966,062 shares, 1.5% of the shares of the Company’s common stock outstanding on the last day of the immediately preceding fiscal year, or an amount as determined by the Company’s Board of Directors. The ESPP allows eligible employees to purchase shares of the Company’s common stock at a discount through payroll deductions of up to 15% of their eligible compensation, subject to any plan limitations. The ESPP provides for twelve-month offering periods that each contain two six-month purchase periods. At the end of each purchase period, employees are able to purchase shares at 85% of the lower of the fair market value of the Company’s common stock on the first trading day of the offering period or on the last day of the purchase period. As of September 30, 2017, 105,128 Equity Incentive Plan Activity A summary of share-based awards available for grant under the 2016 Plan is as follows: Options Available for Grant Balance at December 31, 2015 331,938 Additional options authorized 3,865,000 Options granted (466,914 ) Options forfeited 13,013 Balance at December 31, 2016 3,743,037 Additional options authorized 1,106,966 Options granted (800,846 ) Options forfeited 15,415 Balance at September 30, 2017 4,064,572 The following table summarizes stock option activity under the 2006 and 2016 Plans, including grants to non-employees: Options Outstanding Options Outstanding Weighted- Average Exercise Price Per Share Weighted- Average Remaining Contractual Life (years) Aggregate Intrinsic Value (in thousands) Balances at December 31, 2015 2,685,913 $ 4.81 7.63 $ 11,589 Options granted 361,385 15.65 Options exercised (57,067 ) 2.33 Options forfeited (13,013 ) 6.92 Balances at December 31, 2016 2,977,218 6.16 6.93 $ 70,979 Options granted 449,556 36.24 Options exercised (649,213 ) 3.97 Options forfeited (11,659 ) 15.72 Balances at September 30, 2017 2,765,902 $ 11.52 7.29 $ 111,634 Options exercisable – September 30, 2017 1,656,418 $ 5.43 6.36 $ 76,940 Options vested and expected to vest – September 30, 2017 2,698,510 $ 11.21 7.25 $ 109,750 The aggregate intrinsic values of options outstanding, exercisable, vested and expected to vest were calculated as the difference between the exercise price of the options and the closing price of the Company’s common stock. During the nine months ended September 30, 2017 and 2016, the estimated weighted-average grant-date fair value of common stock underlying options granted was $18.50 and $5.78 per share, respectively.

Stock-Based Compensation

Stock-Based Compensation	9 Months Ended
	Sep. 30, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-Based Compensation	13. Stock-Based Compensation Employee Stock Options Valuation The fair value of employee and director stock options was estimated at the date of grant using a Black-Scholes option valuation model with the weighted average assumptions below. Three Months Ended September 30 Nine Months Ended September 30 2017 2016 2017 2016 Expected term (in years) 6.1 6.1 6.1 6.1 Expected volatility 46.9 % 60.0 % 52.1 % 60.0 % Risk-free interest rate 1.94 % 1.28 % 2.07 % 1.45 % Dividend yield 0.0 % 0.0 % 0.0 % 0.0 % Stock-Based Compensation The following table summarizes the total stock-based compensation expense included in the statements of operations and comprehensive loss for all periods presented (in thousands): Three Months Ended September 30 Nine Months Ended September 30 2017 2016 2017 2016 Cost of revenue $ 36 $ 3 $ 112 $ 8 Research and development 446 34 1,198 103 Selling, general and administrative 2,249 364 5,714 1,140 Total stock-based compensation expense $ 2,731 $ 401 $ 7,024 $ 1,251 As September 30, 2017, there was total unamortized compensation costs of $10.1 million, net of estimated forfeitures, related to unvested stock options which the Company expects to recognize over a period of approximately 2.5 years, $12.4 million, net of estimated forfeitures, related to unrecognized restricted stock unit (“RSU”) expense, which the Company expects to recognize over a period of 2.7 years, and $0.4 million unrecognized ESPP expense, which the Company will recognize over years. Non-Employee Stock-Based Compensation Stock-based compensation expense related to stock options granted to non-employees is recognized as the stock options are earned. The measurement of stock-based compensation for non-employees is subject to periodic adjustment as the underlying equity instruments vest, and the related compensation expense is based on the estimated fair value of the equity instruments using the Black-Scholes option pricing model. The Company believes that the estimated fair value of the stock options is more readily measurable than the fair value of the services received. Such expense was not material for the three and nine months ended September 30, 2017 and 2016.

Net Loss Per Common Share

Net Loss Per Common Share	9 Months Ended
	Sep. 30, 2017
Earnings Per Share [Abstract]
Net Loss Per Common Share	14. Net Loss Per Common Share As the Company had net losses for the three and nine months ended September 30, 2017 and 2016, all potential common shares were determined to be anti-dilutive. The following table sets forth the computation of the basic and diluted net loss per share attributable to common stockholders (in thousands, except share and per share data): Three Months Ended September 30, Nine Months Ended September 30, 2017 2016 2017 2016 Numerator: Net loss $ (6,524 ) $ (4,075 ) $ (18,271 ) $ (14,637 ) Denominator: Weighted-average shares used to compute net loss per common share, basic and diluted 22,811,907 1,454,307 22,446,399 1,434,583 Net loss per common share, basic and diluted $ (0.29 ) $ (2.80 ) $ (0.81 ) $ (10.20 ) The following outstanding shares of potentially dilutive securities have been excluded from diluted net loss per common share for the three and nine months ended September 30, 2017 and 2016, because their inclusion would be anti-dilutive: As of September 30, 2017 2016 Convertible preferred stock on an as-if converted basis — 13,343,981 Options to purchase common stock 2,765,902 2,732,538 RSUs issued and unvested 453,063 — Warrants to purchase convertible preferred stock on an as-if converted basis — 328,114 Warrants to purchase common stock 127,918 — Total 3,346,883 16,404,633

Summary of Significant Accoun21

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2017
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying financial statements have been prepared in accordance with generally accepted accounting principles in the United States of America, or U.S. GAAP, and applicable rules and regulations of the Securities and Exchange Commission, or SEC, regarding interim financial reporting. As permitted under those rules, certain footnotes or other financial information that are normally required by GAAP have been condensed or omitted, and accordingly the balance sheet as of December 31, 2016 has been derived from the audited consolidated financial statements at that date but does not include all of the information required by GAAP for complete consolidated financial statements. These unaudited condensed consolidated financial statements have been prepared on the same basis as the Company’s annual consolidated financial statements and, in the opinion of management, reflect all adjustments (consisting only of normal recurring adjustments) that are necessary for the fair statement of the Company’s condensed consolidated financial information. The results of operations for the three and nine months ended September 30, 2017 are not necessarily indicative of the results to be expected for the year ending December 31, 2017 or for any other interim period or for any other future year. The accompanying interim unaudited condensed consolidated financial statements and related financial information should be read in conjunction with the audited financial statements and the related notes thereto for the year ended December 31, 2016 included in the Company’s Form 10-K, filed with the SEC on March 31, 2017.
Principals of Consolidation	Principles of Consolidation The accompanying interim unaudited condensed consolidated financial statements are consolidated for the nine months ended September 30, 2017 and 2016 and include the accounts of iRhythm Technologies, Inc. and its wholly-owned subsidiary, iRhythm Technologies Ltd., established in March 2016. The financial statements of iRhythm Technologies Ltd. use the U.S. dollar as the functional currency . For all non-functional currency balances, the remeasurement of such balances to functional currency results in a foreign exchange transaction gain or loss, which is recorded in the consolidated statements of operations.
Use of Estimates	Use of Estimates The preparation of the condensed 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 financial statements and the reported amounts of revenues and expenses during the reporting period. On an ongoing basis, management evaluates its estimates, including those related to revenue recognition, contractual allowances for revenue, allowance for doubtful accounts, the useful lives of property and equipment, the recoverability of long-lived assets including the estimated usage of the printed circuit board assemblies (“PCBAs”), the valuation of deferred tax assets, the fair value of the Company’s preferred and common stock and stock-based compensation. The Company bases these estimates on historical and anticipated results, trends, and various other assumptions that the Company believes are reasonable under the circumstances, including assumptions as to future events. Actual results may differ from those estimates.
Fair Value of Financial Instruments	Fair Value of Financial Instruments The carrying amounts of certain of the Company’s financial instruments, which include cash equivalents, short-term investments, accounts receivable, accounts payable and accrued liabilities, approximate fair value due to their short maturities.
Cash Equivalents	Cash Equivalents Cash equivalents consist of short-term, highly liquid investments with original maturities of three months or less from the date of purchase.
Investments	Investments Short-term investments consist of debt securities classified as available-for-sale and have maturities greater than 90 days, but less than 365 days from the date of acquisition. Long-term investments have maturities greater than 365 days as of the balance sheet date. All investments are carried at fair value based upon quoted market prices. Unrealized gains and losses on available-for-sale securities are excluded from earnings and are reported as a component of accumulated other comprehensive loss. The cost of available-for-sale securities sold is based on the specific-identification method. Realized gains and losses are included in earnings, and are derived for specific-identification method for determining the costs of investments sold.
Restricted Cash	Restricted Cash Restricted cash consists of certificates of deposit held with a financial institution as security deposits for building leases and is included in short-term assets on the Company's condensed consolidated balance sheets.
Accounts Receivable, Allowance for Doubtful Accounts and Contractual Allowance	Accounts Receivable, Allowance for Doubtful Accounts and Contractual Allowance Accounts receivable consists of amounts due to the Company from institutions, government payors and third-party commercial payors as a result of the Company's normal business activities. Accounts receivable is reported on the condensed consolidated balance sheets net of an estimated allowance for doubtful accounts and contractual allowance. The Company establishes an allowance for doubtful accounts for estimated uncollectible receivables based on its historical experience, and recognizes the provision as a component of selling, general and administrative expenses. The Company establishes a contractual allowance, which is a reduction in revenue, for estimated uncollectible amounts from Centers for Medicare & Medicaid Services (“CMS”) and contracted third-party commercial payors. The following table presents the changes in the allowance for doubtful accounts: September 30, December 31, 2017 2016 Balance, beginning of period $ 1,792 $ 1,125 Add: provision for doubtful accounts 1,855 1,960 Less: write-offs, net of recoveries and other adjustments (852 ) (1,293 ) Balance, end of period $ 2,795 $ 1,792 The following table presents the changes in the contractual allowance: September 30, December 31, 2017 2016 Balance, beginning of period $ 2,340 $ 338 Add: contractual allowances 4,072 2,726 Less: write-offs, net of recoveries and other adjustments (678 ) (724 ) Balance, end of period $ 5,734 $ 2,340 Management reviews and updates its estimates for the allowances for doubtful accounts and contractual allowance periodically to reflect its experience regarding historical collections. If management were to make different judgments or utilize different estimates in the allowances for doubtful accounts and contractual allowance, differences in the amount of reported selling, general and administrative expenses and revenue could result, respectively.
Concentration of Credit Risk	Concentrations of Risk Credit Risk Financial instruments that potentially subject the Company to a concentration of credit risk consist primarily of cash and cash equivalents, investments and accounts receivable. Cash, cash equivalents, and investments are deposited in financial institutions which, at times, may be in excess of federally insured limits. Cash equivalents are invested in highly rated money market funds. The Company invests in a variety of financial instruments, such as, but not limited to, United States Government securities, corporate notes, commercial paper and, by policy, limits the amount of credit exposure with any one financial institution or commercial issuer. The Company has not experienced any material losses on its deposits of cash and cash equivalents or investments. Concentrations of credit risk with respect to accounts receivable are limited due to the large number of customers comprising the Company’s customer base and their dispersion across many geographies. The Company does not require collateral. The Company records an allowance for doubtful accounts when it becomes probable that a receivable will not be collected. Government agencies, including CMS and the Veterans Administration, accounted for approximately 39%, 38%, 38% and 40% of the Company’s revenue for the three and nine months ended September 30, 2017 and 2016 respectively. Accounts receivable related to government agencies accounted for 26% and 27% at September 30, 2017 and December 31, 2016, respectively.
Concentration of Supply Risk	Supply Risk While the Company has not experienced manufacturing supply disruptions to date, the Company relies on single-source vendors for the supply of its disposable housings, instruments and other materials used to manufacture the ZIO Patch and the adhesive that binds the ZIO Patch to a patient’s body. These components and materials are critical, and there could be a considerable delay in finding alternative sources of supply.
Inventory	Inventory Inventory is stated at the lower of cost or net realizable value, cost being determined on a standard cost basis for material costs and on actual cost basis for labor and overhead, which approximates actual cost on a first in, first out (“FIFO)” basis, and market being determined as the lower of cost or net realizable value. The Company records write-downs of inventory that is obsolete or in excess of anticipated demand or market value based on consideration of product lifecycle stage, technology trends, product development plans and assumptions about future demand and market conditions. Actual demand may differ from forecasted demand and such differences may have a material effect on recorded inventory values. Inventory write-downs are charged to cost of revenue and establish a new cost basis for the inventory.
Property and Equipment	Property and Equipment Property and equipment are stated at cost less accumulated depreciation and amortization. Depreciation and amortization is computed using the straight-line method over the estimated useful lives of the assets, ranging from three to five years. Leasehold improvements are amortized over the shorter of the lease term or the estimated useful lives of the assets. Maintenance and repairs are charged to expense as incurred and improvements and betterments are capitalized.
Internal-Use Software	Internal-Use Software The Company capitalizes costs related to internal-use software during the application development stage. Costs related to planning and post implementation activities are expensed as incurred. Capitalized internal-use software is amortized, and recognized as cost of revenue, on a straight-line basis over the estimated useful life, which is up to five years. The Company evaluates the useful lives of these assets on an annual basis and tests for impairment whenever events or changes in circumstances occur that could impact the recoverability of these assets. Capitalized internal-use software costs are classified as a component of property and equipment.
Goodwill	Goodwill Goodwill represents the excess of the purchase price paid over the fair value of tangible and identifiable intangible net assets acquired in business combinations. Goodwill is tested for impairment on an annual basis and at any other time if events occur or circumstances indicate that the carrying amount of goodwill may not be recoverable. Such events or circumstances may include significant adverse changes in the general business climate, among other things. The impairment test is performed by determining the enterprise fair value of the Company, which is primarily based on the Company’s market capitalization. If the Company’s carrying value, as a one reporting unit entity, is less than its fair value, then the fair value is allocated to all of its assets and liabilities (including any unrecognized intangible assets) as if the fair value was the purchase price to acquire the Company. The excess of the fair value over the amounts assigned to the Company’s assets and liabilities is the implied fair value of the goodwill. If the carrying amount of goodwill exceeds the implied fair value of that goodwill, an impairment loss is recognized in an amount equal to that excess. The Company performs its annual evaluation of goodwill during the fourth quarter of each fiscal year. The Company did not record any charges related to goodwill impairment in any of the periods presented in these condensed consolidated financial statements.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets The Company annually reviews long-lived assets 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 cash flows which the assets are expected to generate. If such assets are considered to be impaired, the impairment to be recognized is measured as the amount by which the carrying amount of the assets exceeds the projected discounted future net cash flows arising from the asset. To date there have been no such impairments of long-lived assets.
Other Assets	Other Assets Included in the other assets are PCBAs totaling $3.5 million and $2.8 million as of September 30, 2017 and December 31, 2016, respectively. The Company uses a PCBA in each wearable device and it is used numerous times and has a useful life beyond one year. Each time the PCBA is used in a wearable device, a portion of the cost of the PCBA is recorded as a cost of revenue. The Company has based its estimates of how many times a PCBA can be used on testing in research and development, loss rates, product obsolescence, and the amount of time it takes the device to go through the manufacturing, shipping, customer shelf and patient wear time and upload process. The Company periodically evaluates the use estimate.
Comprehensive Loss	Comprehensive Loss Comprehensive loss represents all changes in stockholders' equity except those resulting from and distributions to stockholders. The Company’s unrealized gains and losses on available-for-sale securities represent the only component of other comprehensive loss that are excluded from the reported net loss and that are presented in the condensed consolidated statements of comprehensive loss.
Revenue Recognition	Revenue Recognition The Company’s devices, cardiac rhythm monitors, have a wear period for up to 14 days for the ZIO Service or 30 days for the ZIO Event Card. The Company's services, consisting of the delivery of reports containing analysis of data captured by the physical device to the prescribing physician, are generally billable at the start of the wear period or when reports are issued to physicians, depending on the service provided. For the ZIO Event Card, the Company recognizes revenue on a straight-line basis over the applicable wear period, as the event monitoring results are delivered to physicians. For the ZIO Service, the Company recognizes the revenue at the time that a report is delivered to a physician. For all services performed, the Company considers whether or not the following revenue recognition criteria are met: persuasive evidence of an arrangement exists and delivery has occurred or services have been rendered. For services performed for customers the Company invoices directly, additional revenue recognition criteria include that the price is fixed and determinable and collectability is reasonably assured; for customers in which the Company submits claims to third-party commercial and governmental payors for reimbursement, it recognizes revenue only when a reasonable estimate of reimbursement can be made. The assessment of whether a reasonable estimate of reimbursement can be made requires significant judgment by management. Where management's judgment indicates a reasonable estimate of reimbursement can be made, revenue is recognized upon delivery of the patient report for the ZIO Service and straight-line for the ZIO Event Card. Some patients have out-of-pocket costs for amounts not covered by their insurance carrier, and the Company may bill the patient directly for these amounts in the form of co-payments and co-insurance in accordance with their insurance carrier and health plans. Some payors may not cover the Company's service as ordered by the prescribing physician under their reimbursement policies. In the absence of an agreement with the patient or other clearly enforceable legal right to demand payment from the patient, the related revenue is recognized upon the earlier of notification of the payor benefits allowed or when payment is received, until the Company has the ability to make a reasonable estimate. Once a reasonable estimate can be made, revenue is recognized upon delivery of the service. During 2017, the Company recognized revenue from certain non-contracted payors as a reasonable estimate was able to be made, primarily based on the consistency of historical payments. The Company recognizes revenue related to billings for CMS and commercial payors on an accrual basis, net of contractual allowances, when a reasonable estimate of reimbursement can be made. These contractual allowances represent the difference between the list price (the billing rate) and the reimbursement rate for each payor. Upon ultimate collection from CMS and commercial payors, the amount is compared to the previous estimates and the contractual allowance is adjusted accordingly. Until a contract has been negotiated with a commercial payor, the Company’s services may or may not be covered by these entities' existing reimbursement policies. In addition, patients do not enter into direct agreements with the Company that commit them to pay any portion of the cost of the service in the event that their insurance declines to reimburse the Company. In the absence of an agreement with the patient or other clearly enforceable legal right to demand payment from the patient, the related revenue is recognized upon the earlier of notification of the payor benefits allowed or when payment is received, until the Company has the ability to make a reasonable estimate. Contracted revenue recognized on an accrual basis was $22.5 million, $13.3 million, $62.1 million and $37.6 million for the three and nine months ended September 30, 2017 and 2016, respectively. Revenue related to non-contracted claims was $2.5 million, $3.5 million, $8.2 million and $7.8 million for the three and nine months ended September 30, 2017 and 2016, respectively. Certain of the Company’s customers pay the Company directly for the ZIO Service upon shipment of devices. Such advance payments are recorded as deferred revenue on the condensed consolidated balance sheets and revenue is recognized when reports are delivered to physicians.
Cost of Revenue	Cost of Revenue Cost of revenue is expensed as incurred and includes direct labor, material costs, equipment and infrastructure expenses, amortization of internal-use software, allocated overhead, and shipping and handling. Material costs include both the disposable costs of the device and amortization of the PCBAs. Each time the PCBA is used in a wearable device, a portion of the cost of the PCBA is recorded as a cost of revenue.
Research and Development	Research and Development The Company’s research and development costs are expensed as incurred. Research and development costs include, but are not limited to, payroll and personnel-related expenses, laboratory supplies, consulting costs and overhead charges.
Income Taxes	Income Taxes The Company uses the asset and liability method to account for income taxes in accordance with the authoritative guidance for income taxes. Under this method, deferred tax assets and liabilities are determined based on future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases, and tax loss and credit carryforwards. Deferred tax assets and liabilities are measured using enacted tax rates applied to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in income in the period that includes the enactment date. A valuation allowance is established when necessary to reduce deferred tax assets to the amount expected to be realized. The Company recognizes the effect of income tax positions only if those positions are more likely than not of being sustained. Recognized income tax positions are measured at the largest amount that is greater than 50% likely of being realized. Changes in recognition or measurement are reflected in the period in which the change in judgment occurs. The Company records interest and penalties related to unrecognized tax benefits in income tax expense. To date, there have been no interest or penalties charged in relation to the unrecognized tax benefits.
Stock-based Compensation	Stock-based Compensation The Company measures its stock-based awards made to employees based on the estimated fair values of the awards as of the grant date. The fair value of stock options are determined using the Black-Scholes option pricing model. Stock-based compensation expense is recognized over the requisite service period using the straight-line method and is based on the value of the portion of stock-based payment awards that is ultimately expected to vest. As such, the Company’s stock-based compensation is reduced for the estimated forfeitures at the date of grant and revised, if necessary, in subsequent periods if actual forfeitures differ from those estimates. For restricted stock, the compensation cost for these awards is based on the closing price of the Company’s common stock on the date of grant, and recognized as compensation expense on a straight-line basis over the requisite service period. The Company recognizes compensation expense related to the Employee Stock Purchase Program (“ESPP”) based on the estimated fair value of the options on the date of grant, net of estimated forfeitures. The Company estimates the grant date fair value, and the resulting stock-based compensation expense, using the Black-Scholes option pricing model for each purchase period. The grant date fair value is expensed on a straight-line basis over the offering period.
Net Loss per Common Share	Net Loss per Common Share Basic net loss per common share is calculated by dividing the net loss by the weighted average number of shares of common stock outstanding during the period, without consideration of potentially dilutive securities. Diluted net loss per common share is the same as basic net loss per common share for all periods presented since the effect of potentially dilutive securities are anti-dilutive.
Reclassification of Prior Year Presentation	Reclassification of Prior Year Presentation Certain prior year amounts have been reclassified for consistency with the current period presentation. These reclassifications had no effect on the Company’s results of operations, net loss or cash flows.
Recent Accounting Pronouncements	Recent Accounting Pronouncements In May 2014, the Financial Accounting Standards Board (“FASB”), issued Accounting Standards Update (“ASU”) Revenue from Contracts with Customers (Topic 606) In addition, Topic 606 requires more detailed disclosures to enable users of financial statements to understand the nature, timing and uncertainty of revenue and cash flows arising from a review of historical accounting policies and practices to identify potential differences in applying Topic 606. The Company plans to adopt this standard on January 1, 2018 and will use the modified retrospective approach recognizing the cumulative effect of adopting this guidance as an adjustment to its opening accumulated deficit balance, which will have no effect on the Company’s consolidated statements of operations or cash flows for the quarter or year ended December 31, 2017. Prior periods will not be retrospectively adjusted. While the evaluation of the new standard is ongoing, the Company believes the adoption will result in a change to net revenue primarily due to the recognition of bad debt expense related to the patient responsibility of both contracted and non-contracted claims, which was $1.7 million for the nine months ended September 30, 2017, as a reduction of gross revenue rather than as a component of selling, general and administrative and, to a lesser extent, due to timing differences in its recognition of revenue related to non-contracted third-party payor claims as a result of changing from recognition based on the earlier of notification of the payor benefits allowed or when payment is received to the accrual basis based on historical experience. In March 2016, the FASB issued ASU No. 2016-09, Compensation—Stock Compensation (Topic 718) On May 10, 2017, the FASB issued ASU 2017-09, Scope of Modification Accounting The Company is currently evaluating the impact of this new guidance.

Summary of Significant Accoun22

Summary of Significant Accounting Policies (Tables)	9 Months Ended
	Sep. 30, 2017
Accounting Policies [Abstract]
Schedule of Changes in Allowance for Doubtful Accounts	The following table presents the changes in the allowance for doubtful accounts: September 30, December 31, 2017 2016 Balance, beginning of period $ 1,792 $ 1,125 Add: provision for doubtful accounts 1,855 1,960 Less: write-offs, net of recoveries and other adjustments (852 ) (1,293 ) Balance, end of period $ 2,795 $ 1,792
Schedule of Changes in Contractual Allowance	The following table presents the changes in the contractual allowance: September 30, December 31, 2017 2016 Balance, beginning of period $ 2,340 $ 338 Add: contractual allowances 4,072 2,726 Less: write-offs, net of recoveries and other adjustments (678 ) (724 ) Balance, end of period $ 5,734 $ 2,340

Cash Equivalents and Investme23

Cash Equivalents and Investments (Tables)	9 Months Ended
	Sep. 30, 2017
Cash And Cash Equivalents [Abstract]
Schedule of Fair Value of Securities, not Including Cash	The fair value of securities, not including cash at September 30, 2017 and December 31, 2016, were as follows (in thousands): September 30, 2017 Amortized Gross Unrealized Estimated Cost Gains Losses Fair Value Money market funds $ 5,722 $ — $ — $ 5,722 U.S. government securities 35,942 1 (26 ) 35,917 Corporate notes 15,669 1 (4 ) 15,666 Commercial paper 48,130 — — 48,130 Total available-for-sale securities $ 105,463 $ 2 $ (30 ) $ 105,435 Classified as: Cash equivalents $ 18,418 Short-term investments 87,017 Total cash equivalents and investments $ 105,435 December 31, 2016 Amortized Gross Unrealized Estimated Cost Gains Losses Fair Value Money market funds $ 45,937 $ — $ — $ 45,937 U.S. government securities 16,479 11 — 16,490 Corporate notes 23,947 — (20 ) 23,927 Commercial paper 24,971 — — 24,971 Total available-for-sale securities $ 111,334 $ 11 $ (20 ) $ 111,325 Classified as: Cash equivalents $ 45,937 Short-term investments 54,407 Long-term investments 10,981 Total cash equivalents and investments $ 111,325
Schedule of Fair Value of Short-term and Long-term Marketable Securities Classified by Maturity	As the carrying value approximates the fair value for the Company’s cash equivalents, short-term and long-term investments shown in the tables above, the following table summarizes the fair value of the Company’s cash equivalents, short-term and long-term investments classified by maturity (in thousands): September 30, December 31, 2017 2016 Due within one year $ 105,435 $ 100,344 Due after one year through three years — 10,981 Total available-for-sale marketable debt securities $ 105,435 $ 111,325

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2017
Fair Value Disclosures [Abstract]
Schedule of Fair Value of Company's Financial Assets and Liabilities	The following table presents the fair value of the Company’s financial assets and liabilities determined using the inputs defined above (amounts in thousands). September 30, 2017 Level 1 Level 2 Level 3 Total Assets Money market funds $ 5,722 $ — $ — $ 5,722 U.S. government securities — 35,917 — 35,917 Corporate notes — 15,666 — 15,666 Commercial paper — 48,130 — 48,130 Total $ 5,722 $ 99,713 $ — $ 105,435 December 31, 2016 Level 1 Level 2 Level 3 Total Assets Money market funds $ 45,937 $ — $ — $ 45,937 U.S. government securities — 16,490 — 16,490 Corporate notes — 23,927 — 23,927 Commercial paper — 24,971 — 24,971 Total $ 45,937 $ 65,388 $ — $ 111,325
Summary of Changes in Fair Value of Preferred Stock Warrants Classified as Level 3	The following table sets forth a summary of the changes in the fair value of the preferred stock warrants which is classified as Level 3 in the fair value hierarchy. Nine Months Ended September 30, 2017 Nine Months Ended September 30, 2016 Beginning balance $ — $ 2,949 Total change in fair value recorded as other expense, net — 996 Ending balance $ — $ 3,945

Balance Sheet Components (Table

Balance Sheet Components (Tables)	9 Months Ended
	Sep. 30, 2017
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Components of Inventory and PCBAs	Inventory and PCBAs consisted of the following (in thousands): September 30, 2017 December 31, 2016 Raw materials $ 737 $ 839 Finished goods 4,119 3,324 Total $ 4,856 $ 4,163 Reported on the consolidated balance sheet as: Inventory $ 1,314 $ 1,390 Other assets 3,542 2,773 Total $ 4,856 $ 4,163
Components of Property and Equipment, Net	Property and equipment, net consisted of the following (in thousands): September 30, December 31, 2017 2016 Laboratory and manufacturing equipment $ 2,028 $ 1,509 Computer equipment and software 916 736 Furniture and fixtures 928 657 Leasehold improvements 703 502 Internal-use software 4,387 2,900 Total property and equipment, gross 8,962 6,304 Less: accumulated depreciation and amortization (2,755 ) (1,651 ) Total property and equipment, net $ 6,207 $ 4,653
Components of Accrued Liabilities	Accrued liabilities consisted of the following (in thousands): September 30, December 31, 2017 2016 Accrued vacation $ 1,923 $ 1,642 Accrued payroll and related expenses 5,627 6,179 Accrued ESPP contributions 1,029 417 Accrued professional services fees 555 636 Other 2,302 1,291 Total accrued liabilities $ 11,436 $ 10,165

Commitments and Contingencies (

Commitments and Contingencies (Tables)	9 Months Ended
	Sep. 30, 2017
Commitments And Contingencies Disclosure [Abstract]
Schedule of Future Minimum Lease Payments Under Non-cancelable Operating Leases	The following table summarizes the Company’s future minimum lease payments as of September 30, 2017 (in thousands): Period Ending December 31: 2017 (remainder of year) $ 1,263 2018 5,089 2019 5,108 2020 1,178 2021 406 Thereafter 2,541 Total $ 15,585

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	9 Months Ended
	Sep. 30, 2017
Equity [Abstract]
Schedule of Common Stock Shares Reserved for Future Issuance	The Company had reserved shares of common stock for issuance as follows: September 30, December 31, 2017 2016 Options issued and outstanding 2,765,902 2,977,218 Unvested restricted stock units 453,063 105,529 Common stock warrants issued and outstanding 127,918 217,245 Shares available for grant under future stock plans 4,774,565 4,226,068 8,121,448 7,526,060

Stock Incentive Plans (Tables)

Stock Incentive Plans (Tables)	9 Months Ended
	Sep. 30, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Summary of Share-based Awards Available for Grant under 2016 Plan	A summary of share-based awards available for grant under the 2016 Plan is as follows: Options Available for Grant Balance at December 31, 2015 331,938 Additional options authorized 3,865,000 Options granted (466,914 ) Options forfeited 13,013 Balance at December 31, 2016 3,743,037 Additional options authorized 1,106,966 Options granted (800,846 ) Options forfeited 15,415 Balance at September 30, 2017 4,064,572
Summary of Stock Option Activity Under 2006 and 2016 Plans, Including Grants to Non-employees	The following table summarizes stock option activity under the 2006 and 2016 Plans, including grants to non-employees: Options Outstanding Options Outstanding Weighted- Average Exercise Price Per Share Weighted- Average Remaining Contractual Life (years) Aggregate Intrinsic Value (in thousands) Balances at December 31, 2015 2,685,913 $ 4.81 7.63 $ 11,589 Options granted 361,385 15.65 Options exercised (57,067 ) 2.33 Options forfeited (13,013 ) 6.92 Balances at December 31, 2016 2,977,218 6.16 6.93 $ 70,979 Options granted 449,556 36.24 Options exercised (649,213 ) 3.97 Options forfeited (11,659 ) 15.72 Balances at September 30, 2017 2,765,902 $ 11.52 7.29 $ 111,634 Options exercisable – September 30, 2017 1,656,418 $ 5.43 6.36 $ 76,940 Options vested and expected to vest – September 30, 2017 2,698,510 $ 11.21 7.25 $ 109,750

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	9 Months Ended
	Sep. 30, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Schedule of Fair Value of Employee and Director Stock Options Estimated Using Weighted Average Assumptions	The fair value of employee and director stock options was estimated at the date of grant using a Black-Scholes option valuation model with the weighted average assumptions below. Three Months Ended September 30 Nine Months Ended September 30 2017 2016 2017 2016 Expected term (in years) 6.1 6.1 6.1 6.1 Expected volatility 46.9 % 60.0 % 52.1 % 60.0 % Risk-free interest rate 1.94 % 1.28 % 2.07 % 1.45 % Dividend yield 0.0 % 0.0 % 0.0 % 0.0 %
Summary of Total Stock-Based Compensation Expense Included in Statements of Operations and Comprehensive Loss	The following table summarizes the total stock-based compensation expense included in the statements of operations and comprehensive loss for all periods presented (in thousands): Three Months Ended September 30 Nine Months Ended September 30 2017 2016 2017 2016 Cost of revenue $ 36 $ 3 $ 112 $ 8 Research and development 446 34 1,198 103 Selling, general and administrative 2,249 364 5,714 1,140 Total stock-based compensation expense $ 2,731 $ 401 $ 7,024 $ 1,251

Net Loss Per Common Share (Tabl

Net Loss Per Common Share (Tables)	9 Months Ended
	Sep. 30, 2017
Earnings Per Share [Abstract]
Computation of Basic and Diluted Net Loss per Share Attributable to Common Stockholders	The following table sets forth the computation of the basic and diluted net loss per share attributable to common stockholders (in thousands, except share and per share data): Three Months Ended September 30, Nine Months Ended September 30, 2017 2016 2017 2016 Numerator: Net loss $ (6,524 ) $ (4,075 ) $ (18,271 ) $ (14,637 ) Denominator: Weighted-average shares used to compute net loss per common share, basic and diluted 22,811,907 1,454,307 22,446,399 1,434,583 Net loss per common share, basic and diluted $ (0.29 ) $ (2.80 ) $ (0.81 ) $ (10.20 )
Schedule of Anti-dilutive Securities Excluded from Diluted Net Loss per Common Share	The following outstanding shares of potentially dilutive securities have been excluded from diluted net loss per common share for the three and nine months ended September 30, 2017 and 2016, because their inclusion would be anti-dilutive: As of September 30, 2017 2016 Convertible preferred stock on an as-if converted basis — 13,343,981 Options to purchase common stock 2,765,902 2,732,538 RSUs issued and unvested 453,063 — Warrants to purchase convertible preferred stock on an as-if converted basis — 328,114 Warrants to purchase common stock 127,918 — Total 3,346,883 16,404,633

Summary of Significant Accoun31

Summary of Significant Accounting Policies - Schedule of Changes in Allowance for Doubtful Accounts (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Receivables [Abstract]
Balance, beginning of period	$ 1,792	$ 1,125
Add: provision for doubtful accounts	1,855	1,960
Less: write-offs, net of recoveries and other adjustments	(852)	(1,293)
Balance, end of period	$ 2,795	$ 1,792

Summary of Significant Accoun32

Summary of Significant Accounting Policies - Schedule of Changes in Contractual Allowance (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Receivables [Abstract]
Balance, beginning of period	$ 2,340	$ 338
Add: contractual allowances	4,072	2,726
Less: write-offs, net of recoveries and other adjustments	(678)	(724)
Balance, end of period	$ 5,734	$ 2,340

Summary of Significant Accoun33

Summary of Significant Accounting Policies - Additional Information (Details) - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Summary Of Significant Accounting Policies [Line Items]
Impairment long-lived assets			$ 0
Income tax position likely of being realized upon ultimate settlement			greater than 50%
Unrecognized tax benefits, income tax interest or penalties charge			$ 0
ASU 2014-09 | Bad Debt Expense | Contracted and Non-Contracted Claims
Summary Of Significant Accounting Policies [Line Items]
Change in net revenue due to adoption of new standard			1,700,000
ASU No. 2016-09
Summary Of Significant Accounting Policies [Line Items]
Increase in NOL related to deferred tax assets			$ 100,000
ZIO Event Card
Summary Of Significant Accounting Policies [Line Items]
Equipment wear period			30 days
Internal-Use Software
Summary Of Significant Accounting Policies [Line Items]
Estimated useful life			5 years
Printed Circuit Board Assemblies
Summary Of Significant Accounting Policies [Line Items]
Total other assets	$ 3,500,000		$ 3,500,000		$ 2,800,000
Minimum
Summary Of Significant Accounting Policies [Line Items]
Property and equipment, estimated useful life			3 years
Maximum
Summary Of Significant Accounting Policies [Line Items]
Property and equipment, estimated useful life			5 years
Maximum | ZIO Patch Service
Summary Of Significant Accounting Policies [Line Items]
Equipment wear period			14 days
Revenue | Customer Concentration Risk | Government Agencies
Summary Of Significant Accounting Policies [Line Items]
Concentration of credit risk	39.00%	38.00%	38.00%	40.00%
Accounts Receivable | Accounts Receivable Concentration Risk | Government Agencies
Summary Of Significant Accounting Policies [Line Items]
Concentration of credit risk			26.00%		27.00%
Revenue Related to Non-contracted Claims
Summary Of Significant Accounting Policies [Line Items]
Revenue recognized	$ 2,500,000	$ 3,500,000	$ 8,200,000	$ 7,800,000
Contracted Revenue Recognized on Accrual Basis
Summary Of Significant Accounting Policies [Line Items]
Revenue recognized	$ 22,500,000	$ 13,300,000	$ 62,100,000	$ 37,600,000

Cash Equivalents and Investme34

Cash Equivalents and Investments - Schedule of Fair Value of Securities, not Including Cash (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Cash And Cash Equivalents [Line Items]
Amortized Cost	$ 105,463	$ 111,334
Gross Unrealized Gains	2	11
Gross Unrealized Losses	(30)	(20)
Estimated Fair Value	105,435	111,325
Cash equivalents	18,418	45,937
Short-term investments	87,017	54,407
Long-term investments		10,981
Total cash equivalents and investments	105,435	111,325
Money Market Funds
Cash And Cash Equivalents [Line Items]
Amortized Cost	5,722	45,937
Estimated Fair Value	5,722	45,937
U.S. Government Securities
Cash And Cash Equivalents [Line Items]
Amortized Cost	35,942	16,479
Gross Unrealized Gains	1	11
Gross Unrealized Losses	(26)
Estimated Fair Value	35,917	16,490
Commercial Paper
Cash And Cash Equivalents [Line Items]
Amortized Cost	48,130	24,971
Estimated Fair Value	48,130	24,971
Corporate Notes
Cash And Cash Equivalents [Line Items]
Amortized Cost	15,669	23,947
Gross Unrealized Gains	1
Gross Unrealized Losses	(4)	(20)
Estimated Fair Value	$ 15,666	$ 23,927

Cash Equivalents and Investme35

Cash Equivalents and Investments - Additional Information (Details)	9 Months Ended
	Sep. 30, 2017
Cash And Cash Equivalents [Abstract]
Available-for-sale securities, weighted average days to maturity	122 days

Cash Equivalents and Investme36

Cash Equivalents and Investments - Schedule of Fair Value of Short-term and Long-term Investments Classified by Maturity (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Marketable Securities [Abstract]
Due within one year	$ 105,435	$ 100,344
Due after one year through three years		10,981
Total available-for-sale marketable debt securities	$ 105,435	$ 111,325

Fair Value Measurements - Sched

Fair Value Measurements - Schedule of Fair Value of Company's Financial Assets and Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Assets
Total financial assets	$ 105,435	$ 111,325
Level 1
Assets
Total financial assets	5,722	45,937
Level 2
Assets
Total financial assets	99,713	65,388
Money Market Funds
Assets
Total financial assets	5,722	45,937
Money Market Funds | Level 1
Assets
Total financial assets	5,722	45,937
U.S. Government Securities
Assets
Total financial assets	35,917	16,490
U.S. Government Securities | Level 2
Assets
Total financial assets	35,917	16,490
Corporate Notes
Assets
Total financial assets	15,666	23,927
Corporate Notes | Level 2
Assets
Total financial assets	15,666	23,927
Commercial Paper
Assets
Total financial assets	48,130	24,971
Commercial Paper | Level 2
Assets
Total financial assets	$ 48,130	$ 24,971

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Details)	9 Months Ended
	Sep. 30, 2017USD ($)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Abstract]
Fair value measurement, liability transfers into level 3, amount	$ 0
Fair value measurement, liability transfers out of level 3, amount	$ 0

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Changes in Fair Value of Preferred Stock Warrants Classified as Level 3 (Details) - Level 3 - Preferred Stock Warrant Liabilities $ in Thousands	9 Months Ended
	Sep. 30, 2016USD ($)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Beginning balance	$ 2,949
Total change in fair value recorded as other expense, net	996
Ending balance	$ 3,945

Balance Sheet Components - Comp

Balance Sheet Components - Components of Inventory and PCBAs (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Inventory [Line Items]
Total inventory and printed circuit board assemblies	$ 4,856	$ 4,163
Inventory	1,314	1,390
Other assets	3,798	3,052
PCBA
Inventory [Line Items]
Other assets	3,542	2,773
Raw Materials
Inventory [Line Items]
Total inventory and printed circuit board assemblies	737	839
Finished Goods
Inventory [Line Items]
Total inventory and printed circuit board assemblies	$ 4,119	$ 3,324

Balance Sheet Components - Co41

Balance Sheet Components - Components of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Property Plant And Equipment [Line Items]
Total property and equipment, gross	$ 8,962	$ 6,304
Less: accumulated depreciation and amortization	(2,755)	(1,651)
Total property and equipment, net	6,207	4,653
Laboratory and Manufacturing Equipment
Property Plant And Equipment [Line Items]
Total property and equipment, gross	2,028	1,509
Computer Equipment and Software
Property Plant And Equipment [Line Items]
Total property and equipment, gross	916	736
Furniture and Fixtures
Property Plant And Equipment [Line Items]
Total property and equipment, gross	928	657
Leasehold Improvements
Property Plant And Equipment [Line Items]
Total property and equipment, gross	703	502
Internal-Use Software
Property Plant And Equipment [Line Items]
Total property and equipment, gross	$ 4,387	$ 2,900

Balance Sheet Components - Addi

Balance Sheet Components - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Property Plant And Equipment [Abstract]
Depreciation and amortization expense	$ 500	$ 200	$ 1,103	$ 646

Balance Sheet Components - Co43

Balance Sheet Components - Components of Accrued Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Payables And Accruals [Abstract]
Accrued vacation	$ 1,923	$ 1,642
Accrued payroll and related expenses	5,627	6,179
Accrued ESPP contributions	1,029	417
Accrued professional services fees	555	636
Other	2,302	1,291
Total accrued liabilities	$ 11,436	$ 10,165

Related-Party Transactions - Ad

Related-Party Transactions - Additional Information (Details) - Kaiser - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Related Party Transaction [Line Items]
Revenue recognized	$ 1	$ 0.4	$ 2.8	$ 1.8
Amounts receivable from transaction	0.7		0.7		$ 0.4
Service related expenses	0.3	$ 0.1	0.5	$ 0.5
Accounts payable and accrued liabilities	$ 0.3		$ 0.3		$ 0.2
Convertible Preferred Stock
Related Party Transaction [Line Items]
Convertible preferred stock, ownership percentage					6.10%

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Commitments And Contingencies Disclosure [Abstract]
Commercial building lease agreement entered date			2017-05
Commercial building lease agreement expiration date			2027-09
Rent Expense	$ 1.3	$ 0.6	$ 3.8	$ 1.6

Commitments and Contingencies46

Commitments and Contingencies - Future Minimum Lease Payments Under Non-cancelable Operating Leases (Details) $ in Thousands	Sep. 30, 2017USD ($)
Operating Leases Future Minimum Payments Due [Abstract]
2017 (remainder of year)	$ 1,263
2,018	5,089
2,019	5,108
2,020	1,178
2,021	406
Thereafter	2,541
Total	$ 15,585

Debt - Additional Information (

Debt - Additional Information (Details)	1 Months Ended				9 Months Ended	12 Months Ended
	Jun. 30, 2017USD ($)	Dec. 31, 2015USD ($)Tranche	Jun. 30, 2014USD ($)$ / sharesshares	Nov. 30, 2012USD ($)shares	Sep. 30, 2017USD ($)	Dec. 31, 2021USD ($)	Dec. 31, 2016USD ($)	Dec. 01, 2016USD ($)	Aug. 31, 2016USD ($)	Dec. 04, 2015USD ($)	Jun. 30, 2015$ / sharesshares
Series D Preferred Stock
Debt Instrument [Line Items]
Warrants issued to purchase shares | shares			20,136
Exercise price of warrants | $ / shares			$ 7.31
CHCF Note
Debt Instrument [Line Items]
Debt instrument maturity date				Nov. 30, 2016
Debt balance					$ 1,600,000		$ 1,500,000
Proceeds from long-term debt, net of issuance costs				$ 1,500,000
Debt instrument accrues simple interest rate				2.00%
Debt instrument extended maturity date					May 31, 2018
CHCF Note | Series D Preferred Stock
Debt Instrument [Line Items]
Warrants issued to purchase shares | shares				22,807							8,552
Exercise price of warrants | $ / shares											$ 6.58
Pharmakon Loan Agreement
Debt Instrument [Line Items]
Maximum borrowing capacity		$ 55,000,000
Number of tranches for loans | Tranche		2
Paid in kind, interest percentage					50.00%
Debt instrument, covenant description					The Company is subject to a financial covenant related to minimum trailing revenue targets that begins in June 2017, and is tested on a semi-annual basis. The minimum net revenue covenant ranges from $44.7 million for the period ended June 30, 2017 to $102.6 million for the period ended December 31, 2021. To date all minimum revenue targets have been achieved. The minimum net revenues financial covenant has a 45-day equity cure period following required delivery date of the financial statements.
Debt instrument, covenant compliance minimum net revenue target next twelve months	$ 44,700,000
Debt instrument, covenant equity cure period					45 days
Debt instrument maturity date					Dec. 31, 2021
Debt balance					$ 32,100,000		30,800,000
Pharmakon Loan Agreement | Silicon Valley Bank
Debt Instrument [Line Items]
Repayment of bank debt		$ 4,900,000
Pharmakon Loan Agreement | Scenario Forecast
Debt Instrument [Line Items]
Debt instrument, covenant compliance minimum net revenue fifth year						$ 102,600,000
Pharmakon Loan Agreement | Tranche A Loans
Debt Instrument [Line Items]
Maximum borrowing capacity										$ 30,000,000
Debt instrument, fixed interest rate					9.50%
Debt instrument, periodic payment					quarterly
Debt instrument, interest due and payable					50.00%
Pharmakon Loan Agreement | Tranche B Loans
Debt Instrument [Line Items]
Maximum borrowing capacity								$ 25,000,000
Loan and Security Agreement
Debt Instrument [Line Items]
Proceeds from long-term debt, net of issuance costs			$ 4,900,000
Debt borrowed additional advance			$ 5,000,000
Repayment of debt		4,900,000
Loan and Security Agreement | Series D Preferred Stock
Debt Instrument [Line Items]
Warrants issued to purchase shares | shares			20,136
Exercise price of warrants | $ / shares			$ 7.31
Warrants expiry period					2024-06
SVB Loan Agreement
Debt Instrument [Line Items]
Maximum borrowing capacity		$ 15,000,000
Credit facility expiration date					Dec. 4, 2018
Debt instrument variable rate basis trailing period of revenue		6 months
Borrowing capacity description					Any principal amount outstanding under the SVB revolving credit line shall bear interest at a floating rate per annum equal to the rate published by The Wall Street Journal as the “Prime Rate” plus 0.25%, are tied to the Company’s trailing six-month revenue and subject to certain revenue targets. The Company may borrow up to 80% of its eligible accounts receivable, up to the maximum of $15.0 million.
SVB Loan Agreement | San Francisco Office | Standby Letters of Credit
Debt Instrument [Line Items]
Letter of credit									$ 3,100,000
SVB Loan Agreement | Maximum
Debt Instrument [Line Items]
Percentage of eligible accounts receivable for borrowings		80.00%
Credit facility borrowing capacity					$ 7,700,000		$ 2,500,000
SVB Loan Agreement | Prime Rate
Debt Instrument [Line Items]
Debt instrument interest rate spread		0.25%

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Provision or benefit for income taxes	$ 0	$ 0	$ 0	$ 0
Benefit recognized for net operating loss carryforwards	0		0
Benefit recognized for other deferred tax assets	$ 0		$ 0
Unrecognized tax benefit					$ 600,000
Unrecognized tax benefit that affects effective tax rate					$ 0

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Details) - USD ($)	9 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Equity [Abstract]
Common stock, shares authorized	100,000,000	100,000,000
Common stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, par value	$ 0.001	$ 0.001
Dividends declared	$ 0

Stockholders' Equity - Schedule

Stockholders' Equity - Schedule Of Common Stock Shares Reserved For Future Issuance (Details) - shares	Sep. 30, 2017	Dec. 31, 2016
Class Of Stock [Line Items]
Total number of shares reserved for future issuance	8,121,448	7,526,060
Common stock warrants issued and outstanding
Class Of Stock [Line Items]
Total number of shares reserved for future issuance	127,918	217,245
Options Issued and Outstanding
Class Of Stock [Line Items]
Total number of shares reserved for future issuance	2,765,902	2,977,218
Unvested restricted stock units
Class Of Stock [Line Items]
Total number of shares reserved for future issuance	453,063	105,529
Shares Available for Grant Under Future Stock Plans
Class Of Stock [Line Items]
Total number of shares reserved for future issuance	4,774,565	4,226,068

Preferred Stock Warrant Liabi51

Preferred Stock Warrant Liabilities - Additional Information (Details) - USD ($)	May 02, 2017	Oct. 26, 2016	Jun. 30, 2014	Nov. 30, 2012	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Mar. 27, 2013
Class Of Warrant Or Right [Line Items]
Change in fair value of preferred stock warrant liabilities							$ 996,000
Series D Preferred Stock
Class Of Warrant Or Right [Line Items]
Warrants issued to purchase shares			20,136
Exercise price of warrants			$ 7.31
Change in fair value of preferred stock warrant liabilities					$ 15,000		(41,000)
Warrants expiry period						2024-06
Warrant exercised	10,068	10,068
Warrant exercise period	May 2, 2017	Oct. 26, 2016
Issuance of common stock upon exercise of warrants, Shares	8,077	7,310
Series D Preferred Stock | Warrant
Class Of Warrant Or Right [Line Items]
Fair value assumptions, discount rate			30.00%
Fair value warrants recorded as debt discount			$ 100,000
2012 Loan Agreement | Series D Preferred Stock
Class Of Warrant Or Right [Line Items]
Warrants issued to purchase shares								207,177
Change in fair value of preferred stock warrant liabilities					$ 500,000		$ 700,000
Warrant outstanding						127,918
2012 Loan Agreement | Series C Preferred Stock
Class Of Warrant Or Right [Line Items]
Exercise price of warrants				$ 0.001
Warrants term				7 years

Stock Incentive Plans - Additio

Stock Incentive Plans - Additional Information (Details)	1 Months Ended	9 Months Ended		12 Months Ended
	Oct. 31, 2016shares	Sep. 30, 2017Period$ / sharesshares	Sep. 30, 2016$ / shares	Dec. 31, 2016shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options granted during the period		449,556		361,385
Shares available for future issuance		8,121,448		7,526,060
Estimated weighted-average grant date fair value of common stock underlying options granted | $ / shares		$ 18.50	$ 5.78
2006 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock option plan, description		Options under the Plan were granted for periods of up to ten years and at the fair value of the shares on the date of grant as determined by the board of directors.
Stock option vesting term		3 years
2006 Equity Incentive Plan | First Anniversary of Grant
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock option exercisable rate, Percentage		25.00%
2006 Equity Incentive Plan | Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock option, period for grant		10 years
2006 Equity Incentive Plan | Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of voting power of all classes of stock		10.00%
2006 Equity Incentive Plan | ISO | Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock option vesting term		5 years
2006 Equity Incentive Plan | Other Options | Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock option vesting term		10 years
2016 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock option plan, description		On the first day of each year beginning with 2017, the 2016 Plan authorizes an annual increase of the least of 3,865,000 shares, 5% of outstanding common stock on the last day of the immediately preceding fiscal year or an amount as determined by the Company's Board of Directors.
Effective date	Oct. 19, 2016
Options granted during the period	0
Shares available for future issuance	3,865,000	4,971,966
Percentage of outstanding common stock increased annually under the plan	5.00%
2016 Plan | Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock option, period for grant		10 years
2016 Plan | Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of stock option exercise price of fair market value of common stock	100.00%
Employee Stock Purchase Program (“ESPP”)
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Effective date	Oct. 19, 2016
Shares available for future issuance	483,031	709,993
Percentage of outstanding common stock increased annually under the plan	1.50%
Increase in shares available for future issuance	966,062
Offering period		12 months
Number of purchase period | Period		2
Purchase period		6 months
Percentage of employee purchase shares of fair market value	85.00%
Common stock issued to employees		105,128
Employee Stock Purchase Program (“ESPP”) | Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of payroll deductions of eligible compensation	15.00%

Stock Incentive Plans - Summary

Stock Incentive Plans - Summary of Share-based Awards Available for Grant under 2016 Plan (Details) - shares	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options Available for Grant, Options forfeited	11,659	13,013
2016 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options Available for Grant, Beginning balance	3,743,037	331,938
Options Available for Grant, Additional options authorized	1,106,966	3,865,000
Options Available for Grant, Options granted	(800,846)	(466,914)
Options Available for Grant, Options forfeited	15,415	13,013
Options Available for Grant, Ending balance	4,064,572	3,743,037

Stock Incentive Plans - Summa54

Stock Incentive Plans - Summary of Stock Option Activity Under 2006 and 2016 Plans, Including Grants to Non-employees (Details) - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016	Dec. 31, 2015
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Options Outstanding, Beginning balance	2,977,218	2,685,913
Options granted	449,556	361,385
Options exercised	(649,213)	(57,067)
Options forfeited	(11,659)	(13,013)
Options Outstanding, Ending balance	2,765,902	2,977,218	2,685,913
Options exercisable	1,656,418
Options vested and expected to vest	2,698,510
Options Outstanding, Weighted Average Exercise Price Per Share, Beginning Balance	$ 6.16	$ 4.81
Options Outstanding, Weighted Average Exercise Price Per Share, Options granted	36.24	15.65
Options Outstanding, Weighted Average Exercise Price Per Share, Options exercised	3.97	2.33
Options Outstanding, Weighted Average Exercise Price Per Share, Options forfeited	15.72	6.92
Options Outstanding, Weighted Average Exercise Price Per Share, Ending Balance	11.52	$ 6.16	$ 4.81
Options Outstanding, Weighted Average Exercise Price Per Share, Exercisable	5.43
Options Outstanding, Weighted Average Exercise Price Per Share, vested and expected to vest	$ 11.21
Options Outstanding, Weighted- Average Remaining Contractual Life (years)	7 years 3 months 15 days	6 years 11 months 5 days	7 years 7 months 17 days
Options exercisable, Weighted- Average Remaining Contractual Life (years)	6 years 4 months 10 days
Options vested and expected to vest, Weighted- Average Remaining Contractual Life (years)	7 years 3 months
Options Outstanding, Aggregate Intrinsic Value	$ 111,634	$ 70,979	$ 11,589
Options exercisable, Aggregate Intrinsic Value	76,940
Options vested and expected to vest, Aggregate Intrinsic Value	$ 109,750

Stock-Based Compensation - Sche

Stock-Based Compensation - Schedule of Fair Value of Employee and Director Stock Options Estimated Using Weighted Average Assumptions (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Expected term (in years)	6 years 1 month 6 days	6 years 1 month 6 days	6 years 1 month 6 days	6 years 1 month 6 days
Expected volatility	46.90%	60.00%	52.10%	60.00%
Risk-free interest rate	1.94%	1.28%	2.07%	1.45%
Dividend yield	0.00%	0.00%	0.00%	0.00%

Stock-Based Compensation - Summ

Stock-Based Compensation - Summary of Total Stock-Based Compensation Expense Included in Statements of Operations and Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 2,731	$ 401	$ 7,024	$ 1,251
Cost of Revenue
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	36	3	112	8
Research and development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	446	34	1,198	103
Selling, general and administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 2,249	$ 364	$ 5,714	$ 1,140

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Details) $ in Millions	9 Months Ended
	Sep. 30, 2017USD ($)
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total unamortized compensation costs, net of estimated forfeitures related to unvested stock options	$ 10.1
Unamortized compensation costs related to unvested stock options, expected period of recognition	2 years 6 months
Restricted Stock Units ("RSUs")
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total unamortized compensation costs, net of estimated forfeitures related to unvested stock options	$ 12.4
Unamortized compensation costs related to unvested stock options, expected period of recognition	2 years 8 months 13 days
ESPP
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total unamortized compensation costs, net of estimated forfeitures related to unvested stock options	$ 0.4
Unamortized compensation costs related to unvested stock options, expected period of recognition	8 months 13 days

Net Loss Per Common Share - Com

Net Loss Per Common Share - Computation of Basic and Diluted Net Loss per Share Attributable to Common Stockholders (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Numerator:
Net Loss	$ (6,524)	$ (4,075)	$ (18,271)	$ (14,637)
Denominator:
Weighted-average shares used to compute net loss per common share, basic and diluted	22,811,907	1,454,307	22,446,399	1,434,583
Net loss per common share, basic and diluted	$ (0.29)	$ (2.80)	$ (0.81)	$ (10.20)

Net Loss Per Common Share - Sch

Net Loss Per Common Share - Schedule of Anti-dilutive Securities Excluded from Diluted Net Loss per Common Share (Details) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from diluted net loss per common share	3,346,883	16,404,633	3,346,883	16,404,633
Convertible Preferred Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from diluted net loss per common share		13,343,981		13,343,981
Options to Purchase Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from diluted net loss per common share	2,765,902	2,732,538	2,765,902	2,732,538
Restricted Stock Units ("RSUs")
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from diluted net loss per common share	453,063		453,063
Warrants to Purchase Convertible Preferred Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from diluted net loss per common share		328,114		328,114
Warrants to Purchase Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from diluted net loss per common share	127,918		127,918