Natera (NTRA) 10-K 26 Feb 21 2020 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Feb. 19, 2021	Jun. 30, 2020
Document and Entity Information
Document Type	10-K
Document Annual Report	true
Document Transition Report	false
Document Period End Date	Dec. 31, 2020
Entity File Number	001-37478
Entity Registrant Name	NATERA, INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	01-0894487
Entity Address, Address Line One	13011 McCallen Pass
Entity Address, Address Line Two	Building A Suite 100
Entity Address, City or Town	Austin
Entity Address, State or Province	TX
Entity Address, Postal Zip Code	78753
City Area Code	650
Local Phone Number	249-9090
Title of 12(b) Security	Common Stock, par value $0.0001 per share
Trading Symbol	NTRA
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Public Float			$ 3,510
Entity Common Stock, Shares Outstanding		86,574,688
Entity Central Index Key	0001604821
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Amendment Flag	false

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 48,668	$ 61,926
Restricted cash	187	55
Short-term investments	688,606	379,065
Accounts receivable, net of allowance of $3,080 in 2020 and $2,919 in 2019	78,565	53,351
Inventory	20,031	12,394
Prepaid expenses and other current assets, net	26,606	16,376
Total current assets	862,663	523,167
Property and equipment, net	33,348	23,283
Operating lease right-of-use assets	21,399	23,730
Other assets	14,743	12,476
Total assets	932,153	582,656
Current liabilities:
Accounts payable	8,096	8,604
Accrued compensation	30,371	16,088
Other accrued liabilities	60,407	49,043
Deferred revenue, current portion	50,125	56,016
Short-term debt financing	50,054	50,123
Total current liabilities	199,053	179,874
Long-term debt financing	202,493	73,656
Deferred revenue, long-term portion	22,805	23,808
Operating lease liabilities, long-term portion	21,246	26,297
Other long-term liabilities	320	310
Total liabilities	445,917	303,945
Commitments and contingencies (Note 8)
Stockholders' equity:
Common stock, $0.0001 par value: 750,000 shares authorized at December 31, 2020 and 2019, respectively; 86,223 and 78,005 shares issued and outstanding at December 31, 2020 and 2019, respectively	9	8
Additional paid in capital	1,411,286	976,955
Accumulated deficit	(929,318)	(699,171)
Accumulated other comprehensive gain	4,259	919
Total stockholders' equity	486,236	278,711
Total liabilities and stockholders' equity	$ 932,153	$ 582,656

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Consolidated Balance Sheets
Allowances on accounts receivable	$ 3,080	$ 2,919
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Common stock, shares authorized	750,000,000	750,000,000
Common stock, shares issued	86,223,000	78,005,000
Common stock, shares outstanding	86,223,000	78,005,000

Consolidated Statements of Oper

Consolidated Statements of Operations and Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenues
Total revenues	$ 391,005	$ 302,328	$ 257,654
Cost and expenses
Research and development	100,035	51,357	51,355
Selling, general and administrative	303,627	206,176	154,872
Gain from disposal of business		(14,388)
Total cost and expenses	607,282	418,615	372,282
Loss from operations	(216,277)	(116,287)	(114,628)
Interest expense	(15,082)	(10,693)	(10,476)
Interest and other (expense) income, net	7,562	4,152	(2,729)
Loss on debt extinguishment	(5,848)
Loss before income taxes	(229,645)	(122,828)	(127,833)
Income tax expense	(98)	(1,999)	(321)
Net loss	(229,743)	(124,827)	(128,154)
Unrealized gain on available-for-sale securities, net of tax	3,340	1,471	214
Comprehensive loss	$ (226,403)	$ (123,356)	$ (127,940)
Net loss per share (Note 14):
Basic and diluted (in dollars per share)	$ (2.84)	$ (1.79)	$ (2.22)
Weighted-average number of shares used in computing basic and diluted net loss per share:
Basic and diluted (in shares)	81,011	69,555	57,848
Product
Revenues
Total revenues	$ 367,211	$ 269,881	$ 240,366
Cost and expenses
Cost of revenues	185,865	162,604	158,081
Licensing and other
Revenues
Total revenues	23,794	32,447	17,288
Cost and expenses
Cost of revenues	$ 17,755	$ 12,866	$ 7,974

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Common stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit	Total
Balance at Dec. 31, 2017	$ 6	$ 472,552	$ (766)	$ (446,375)	$ 25,417
Balance (in shares) at Dec. 31, 2017	54,040,000
Issuance of common stock upon exercise of stock options		13,331			13,331
Issuance of common stock upon exercise of stock options (in shares)	1,967,000
Issuance of common stock under employee stock purchase plan ("ESPP")		3,617			3,617
Issuance of common stock under employee stock purchase plan ("ESPP") (in shares)	391,000
Issuance of common stock upon exercise of warrants		6,762			6,762
Issuance of common stock upon exercise of warrants (in shares)	333,000
Issuance of common stock for offering	$ 1	96,776			96,777
Issuance of common stock for offering (in shares)	5,175,000
Vesting of restricted stock (in shares)	177,000
Stock based compensation		14,198			14,198
Unrealized gain on available-for-sale securities			214		214
Net loss				(128,154)	(128,154)
Balance at Dec. 31, 2018	$ 7	607,236	(552)	(574,529)	32,162
Balance (in shares) at Dec. 31, 2018	62,083,000
Issuance of common stock upon exercise of stock options		13,041			13,041
Issuance of common stock upon exercise of stock options (in shares)	2,464,000
Issuance of common stock under employee stock purchase plan ("ESPP")		4,323			4,323
Issuance of common stock under employee stock purchase plan ("ESPP") (in shares)	268,000
Issuance of common stock for offering	$ 1	323,409			323,410
Issuance of common stock for offering (in shares)	12,624,000
Issuance of common stock to Orbimed		507			507
Issuance of common stock to Orbimed (in shares)	25,000
Vesting of restricted stock (in shares)	541,000
Stock based compensation		28,624			28,624
Unrealized gain on available-for-sale securities			1,471		1,471
Cumulative-effect adjustment upon adoption		(185)		185
Net loss				(124,827)	(124,827)
Balance at Dec. 31, 2019	$ 8	976,955	919	(699,171)	$ 278,711
Balance (in shares) at Dec. 31, 2019	78,005,000				78,005,000
Issuance of common stock upon exercise of stock options		23,524			$ 23,524
Issuance of common stock upon exercise of stock options (in shares)	2,092,000
Issuance of common stock under employee stock purchase plan ("ESPP")		7,114			7,114
Issuance of common stock under employee stock purchase plan ("ESPP") (in shares)	234,000
Issuance of common stock for offering	$ 1	270,649			270,650
Issuance of common stock for offering (in shares)	4,792,000
Vesting of restricted stock (in shares)	1,100,000
Stock based compensation		50,171			50,171
Unrealized gain on available-for-sale securities			3,340		3,340
Cumulative-effect adjustment upon adoption				(404)	(404)
Equity component of Convertible Notes, net		82,873			82,873
Net loss				(229,743)	(229,743)
Balance at Dec. 31, 2020	$ 9	$ 1,411,286	$ 4,259	$ (929,318)	$ 486,236
Balance (in shares) at Dec. 31, 2020	86,223,000				86,223,000

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating activities
Net loss	$ (229,743)	$ (124,827)	$ (128,154)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	8,613	7,730	7,501
Non-cash lease expense	7,834	7,748
Impairment of assets		1,671	1,544
Stock-based compensation	50,171	28,624	14,198
Inventory reserve adjustments	(163)	321	265
Premium amortization and discount accretion on investment securities	5,761	945	238
(Gain) loss on investments	(105)	(16)	43
Loss on sale of property and equipment			(12)
Loss from changes in fair value of warrants			4,118
Interest accrued for borrowings and claims related settlement			2,172
Amortization of debt discount and issuance cost	149	457	391
Other non-cash benefits	(149)	(51)
Gain on disposal of business		(14,388)
Provision for credit losses	1,354	1,141	(41)
Loss on Debt Extinguishment	5,848
Accretion of Convertible Note	7,048
Changes in operating assets and liabilities
Accounts receivable	(25,831)	2,418	(18,093)
Inventory	(7,474)	917	(4,900)
Prepaid expenses and other current assets	(23,386)	(13,956)	2,643
Other assets	(60)	(9,099)	335
Accounts payable	(118)	(6,262)	3,781
Accrued compensation	14,284	3,419	3,069
Other accrued liabilities	10,340	8,606	(1,820)
Deferred revenue	(6,895)	40,848	42,769
Deferred rent, net of current portion			(628)
Other long-term liabilities	10	310
Net cash used in operating activities	(182,512)	(63,444)	(70,581)
Investing activities
Purchases of investments	(685,239)	(446,626)	(170,268)
Proceeds from sale of investments	30,067	1,666	37,387
Proceeds from maturity of investments	343,315	173,900	131,600
Net proceeds from disposal of business		9,675
Purchases of property and equipment, net	(19,604)	(4,968)	(3,880)
Net cash used in investing activities	(331,461)	(266,353)	(5,161)
Financing activities
Proceeds from exercise of stock options	23,524	13,041	13,331
Proceeds from issuance of common stock under employee stock purchase plan	7,114	4,323	3,617
Proceeds from Convertible Note, net of issuance costs	278,316
Loan payment	(78,757)
Proceeds from public offering, net of issuance costs	270,650	323,410	96,777
Net cash provided by financing activities	500,847	340,774	113,725
Net increase (decrease) in cash, cash equivalents and restricted cash	(13,126)	10,977	37,983
Cash, cash equivalents and restricted cash, beginning of period	61,981	51,004	13,021
Cash, cash equivalents and restricted cash, end of period	48,855	61,981	51,004
Supplemental disclosure of cash flow information:
Cash paid for income taxes	67	2,154	332
Cash paid for interest	3,296	12,455	7,914
Non-cash investing and financing activities:
Purchases of property and equipment in accounts payable and accruals	$ 2,781	$ 3,706	$ 268
Issuance of common stock for exercise of warrants			6,762

Description of Business

Description of Business	12 Months Ended
	Dec. 31, 2020
Description of Business
Description of Business	1 . Description of Business Natera, Inc. (the "Company") was formed in the state of California as Gene Security Network, LLC in November 2003 and incorporated in the state of Delaware in January 2007. The Company’s mission is to change the management of disease worldwide, focusing on women's health, oncology, and organ health. The Company operates laboratories certified under the Clinical Laboratory Improvement Amendments ("CLIA") providing a host of cell-free DNA-based molecular testing services. The Company determines its operating segments based on the way it organizes its business to make operating decisions and assess performance. The Company operates one segment, the development and commercialization of molecular testing services, applying its proprietary technology in the fields of women’s health, oncology and organ health. The Company also has a subsidiary that operates in the state of Texas. The Company's product offerings include its Panorama Non-Invasive Prenatal Test ("NIPT") that screens for chromosomal abnormalities of a fetus as well as in twin pregnancies, typically with a blood draw from the mother; Vistara (“Vistara”), a single-gene mutations screening test performed to identify single-gene disorders; Horizon Carrier Screening ("HCS") to determine carrier status for a large number of severe genetic diseases that could be passed on to the carrier’s children; Spectrum Pre-implantation Genetics (“Spectrum”) to evaluate embryos to identify chromosomal anomalies or inherited genetic conditions to improve the chances of a healthy pregnancy during an in vitro fertilization ("IVF") cycle; Anora Miscarriage Test to rapidly and extensively analyze fetal chromosomes to understand the cause of miscarriage; Non-Invasive Paternity Testing ("PAT"), which is exclusively marketed and sold by a licensee from whom the Company receives a royalty; Signatera, which detects circulating tumor DNA in patients previously diagnosed with cancer to assess molecular residual disease and monitor for recurrence; and Prospera, to assess organ transplant rejection. All testing is available principally in the United States. The Company also offers its Panorama test to customers outside of the United States, primarily in Europe. The Company also offers Constellation, a cloud-based software platform that enables laboratory customers to gain access through the cloud to the Company’s algorithms and bioinformatics in order to validate and launch tests based on the Company’s technology. Through the third quarter of 2019, the Company offered Evercord for the collection and storage of newborn cord blood and cord tissue units, which was sold in the third quarter of 2019 to a third-party buyer.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2020
Summary of Significant Accounting Policies
Summary of Significant Accounting Policies	2 Summary of Significant Accounting Policies ​ Basis of Presentation ​ The accompanying consolidated financial statements have been prepared in conformity with U.S. generally accepted accounting principles (“U.S. GAAP”). ​ Liquidity Matters ​ The Company has incurred net losses since its inception and anticipates net losses and negative operating cash flows for the near future. For the year ended December 31, 2020, the Company had a net loss of $229.7 million and an accumulated deficit to $929.3 million. At December 31, 2020, the Company had $48.9 million in cash, cash equivalents and restricted cash, $688.6 million in marketable securities, $50.1 million of outstanding balance of the Credit Line (as defined in Note 10) including accrued interest, and $287.5 million outstanding principal balance of the its 2.25% Convertible Senior Notes (the “Convertible Notes”). The Company used a portion of the net proceeds from the offering of the Convertible Notes to repay its obligations under its 2017 Term Loan with OrbiMed (see Note 10, Debt ​ While the Company has introduced multiple products that are generating revenues, these revenues have not been sufficient to fund all operations. Accordingly, the Company has funded the portion of operating costs that exceeds revenues through a combination of equity issuances, debt issuances, and other financings. The Company continues to develop and commercialize future products and, consequently, it will need to generate additional revenues to achieve future profitability and may need to raise additional equity or debt financing. If the Company raises additional funds by issuing equity securities, its stockholders will experience dilution. Additional debt financing, if available, may involve covenants restricting its operations or its ability to incur additional debt. Any additional debt financing or additional equity that the Company raises may contain terms that are not favorable to it or its stockholders and requires significant debt service payments, which diverts resources from other activities. Additional financing may not be available at all, or in amounts or on terms acceptable to the Company. If the Company is unable to obtain additional financing, it may be required to delay the development and commercialization of its products and significantly scale back its business and operations. In April 2019, the Company completed an underwritten equity offering and sold 6,052,631 shares of its common stock at a price of $19 per share to the public. Before offering expenses of $0.6 million, the Company received proceeds of $108.1 million net of the underwriting discount. In October 2019, the Company completed another underwritten equity offering and sold 6,571,428 shares of its common stock at a price of $35 per share to the public. Before offering expenses of $0.4 million, the Company received proceeds of $216.2 million net of the underwriting discount. In September 2020, the Company completed an additional underwritten equity offering and sold 4,791,665 shares of its common stock at a price of $60.00 per share to the public. Before offering expenses of $0.3 million, the Company received proceeds of $271.0 million net of the underwriting discount. Based on the Company’s current business plan, the Company believes that its existing cash and marketable securities will be sufficient to meet its anticipated cash requirements for at least 12 months after February 25, 2021. ​ Principles of Consolidation ​ The accompanying consolidated financial statements include all the accounts of the Company and its subsidiary. The Company established a subsidiary that operates in the state of Texas to support the Company’s laboratories and operational functions. All intercompany balances and transactions have been eliminated. ​ Use of Estimates ​ ​ Cash and Cash Equivalents ​ Cash and cash equivalents consist of cash and money market deposits with financial institutions. ​ Restricted Cash ​ Restricted cash is currently presented as a separate line item in the Company’s balance sheet. In the statements of cash flows, it is included together with cash and cash equivalents and considered as part of the total ending cash balance. The following is the reconciliation between how restricted cash is presented in the balance sheet and the statements of cash flows for all periods presented: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ December 31, ​ 2020 2019 ​ ​ (in thousands) Cash and cash equivalents in balance sheet ​ $ 48,668 ​ $ 61,926 Restricted cash in balance sheet ​ ​ 187 ​ ​ 55 Total cash, cash equivalents and restricted cash in statements of cash flows ​ $ 48,855 ​ $ 61,981 ​ Investments Investments consist primarily of debt securities such as U.S. Treasuries, U.S. agency and municipal bonds. Management determines the appropriate classification of securities at the time of purchase and re-evaluates such determination at each balance sheet date. The Company generally classifies its entire investment portfolio as available-for-sale. The Company views its available-for-sale portfolio as available for use in current operations. Accordingly, the Company classifies all investments as short-term, irrespective of maturity date. Available-for-sale securities are carried at fair value, with unrealized gains and losses reported in accumulated other comprehensive income (loss), which is a separate component of stockholders’ equity. ​ Fair Value ​ The Company discloses the fair value of financial instruments for financial assets and liabilities for which the value is practicable to estimate. Fair value is defined as the price that would be received upon the sale of an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date (exit price). ​ Risk and Uncertainties ​ The Company is subject to risks and uncertainties as a result of the COVID-19 pandemic. The extent of the impact of the COVID-19 pandemic on the Company's business is highly uncertain and difficult to predict, and the full extent and duration of the impact of the COVID 19 pandemic on our business, our operations, and the global economy as a whole is not yet known. While the Company’s test volumes as well as overall average selling prices increased in the year ended December 31, 2020 compared to the year ended December 31, 2019, the Company cannot predict the potential nature, magnitude and duration of the effects of the COVID-19 pandemic on the macroeconomic environment. Financial instruments that potentially subject the Company to credit risk consist of cash, accounts receivable and investments. The Company limits its exposure to credit loss by placing its cash in financial institutions with high credit ratings. The Company's cash may consist of deposits held with banks that may at times exceed federally insured limits. The Company performs evaluations of the relative credit standing of these financial institutions and limits the amount of credit exposure with any one institution. The Company performs evaluations of financial conditions for insurance carriers, patients, clinics and laboratory partners and generally does not require collateral to support credit sales. For the years ended December 31, 2020, 2019, and 2018, there were no customers exceeding 10% of total revenues on an individual basis. As of December 31, 2020 and 2019, there were no customers with an outstanding balance exceeding 10% of net accounts receivable. ​ Credit Losses ​ Trade accounts receivable and other receivables. ​ The following is a roll-forward of the allowances for credit losses related to trade accounts receivable and other receivables for the year ended December 31, 2020: ​ ​ ​ ​ ​ ​ December 31, ​ ​ 2020 ​ ​ ​ (in thousands) Beginning balance ​ $ 2,919 Cumulative-effect adjustment upon adoption of ASU 2016-13 ​ ​ 404 Provision for credit losses ​ ​ 1,354 Write-offs ​ ​ (457) Total ​ $ 4,220 ​ Available-for-sale debt securities. The amended guidance from ASU 2016-13 requires the measurement of expected credit losses for available-for-sale debt securities held at the reporting date over the remaining life based on historical experience, current conditions, and reasonable and supportable forecasts. The Company evaluated its investment portfolio under the new available-for-sale debt securities impairment model guidance. The vast majority of the Company’s investment portfolio are low risk, investment grade securities. ​ Revenue Recognition ​ The Company adopted the new revenue recognition guidance, ASC 606, beginning January 1, 2018 on a full retrospective basis. ASC 606 mandates revenue recognition to be evaluated using the following five steps: ​ ● Identification of a contract, or contracts, with a customer; ● Identification of the performance obligations in the contract; ● Determination of the transaction price; ● Allocation of the transaction price to the performance obligations in the contract; and ● Revenue recognition when, or as, the performance obligations are satisfied ​ Revenue Recognition, ​ Cost of Product Revenues ​ The components of our cost of product revenues are material and service costs, impairment charges associated with testing equipment, personnel costs, including stock-based compensation expense, equipment and infrastructure expenses associated with testing samples, electronic medical records, order and delivery systems, shipping charges to transport samples, costs incurred from third party test processing fees, and allocated overhead such as rent, information technology costs, equipment depreciation and utilities. Costs associated with Whole Exome Sequencing (“WES”) are also included, as well as labor costs, relating to our Signatera CLIA offering. Costs associated with performing tests are recorded when the test is accessioned. We expect cost of product revenues in absolute dollars to increase as the number of tests we perform increases. ​ ​ Cost of Licensing and Other Revenues ​ The components of our cost of licensing and other revenues are material costs associated with test kits sold to Constellation clients, development and support services relating to our Strategic Partnership Agreements, and costs associated with specimens and Whole Exome Sequencing (“WES”), as well as labor costs, relating to our Signatera (RUO) offering. ​ We currently have 15 revenue generating licensing and service agreements with laboratories under our Constellation distribution model. We consider our cost of licensing and other revenues for the Constellation software platform to be relatively low, and therefore we expect its associated gross margin is higher. We expect our cost of licensing will increase in relation to volume growth. ​ Research and Development ​ The Company records research and development costs in the period incurred. Research and development costs consist of personnel costs, contract services, cost of materials utilized in performing tests, costs of clinical trials and allocated facilities and related overhead expenses. ​ Advertising Costs ​ The Company expenses advertising costs as incurred. The Company incurred advertising costs of $0.6 million, $0.2 million, and $0.2 million for the years ended December 31, 2020, 2019, and 2018, respectively. ​ Product Shipment Costs ​ The Company expenses product shipment costs in cost of product revenues in the accompanying statements of operations. Shipping and handling costs for the years ended December 31, 2020, 2019, and 2018 were $13.3 million, $13.3 million, and $12.4 million, respectively. ​ Income Taxes ​ Income taxes are recorded in accordance with Financial Accounting Standards Board ASC Topic 740, Income Taxes ​ Stock-Based Compensation ​ Stock-based compensation related to stock options and restricted stock units (“RSUs”) granted to the Company’s employees is measured at the grant date based on the fair value of the award. The fair value is recognized as expense over the requisite service period, which is generally the vesting period of the respective awards. No compensation cost is recognized when the requisite service has not been met and the awards are therefore forfeited. ​ For stock options with market conditions, the Company derives the requisite service period using the Monte Carlo simulation model. For stock options and RSUs that vest upon meeting performance conditions or market conditions in combination with performance conditions, the Company derives the requisite service period from the grant date to the date it is probable that the vesting conditions will be met. ​ ​ On January 1, 2019, the Company adopted ASU 2018-07, which allows the accounting for nonemployee awards to be treated the same as for employee awards. The fair value of non-employee awards is now determined based on a one-time measurement at the grant date, and it is no longer subject to periodic remeasurement. The Company continues to recognize stock-based compensation expense as services are rendered by the non-employees over the vesting period, which is accounted for on a straight-line basis. See further discussion under the Recently Adopted Accounting Pronouncements section within this footnote, as well as the election of certain accounting policy as a result of the adoption. ​ The Company uses the Black-Scholes option-pricing model and the Monte Carlo simulation model to estimate the fair value of stock options issued to employees and non-employees. The model requires the input of the Company's expected stock price volatility, the expected term of the awards, and a risk-free interest rate. Determining these assumptions requires significant judgment. See further discussion on the valuation assumptions used under Note 9. ​ Capitalized Software Held for Internal Use ​ The Company capitalizes salaries and related costs of employees and consultants who devote time to the development of internal-use software development projects. Capitalization begins during the application development stage, once the preliminary project stage has been completed, which includes successful validation and approval from management. If a project constitutes an enhancement to previously developed software, the Company assesses whether the enhancement is significant and creates additional functionality to the software, thus qualifying the work incurred for capitalization. Once the project is available for general release, capitalization ceases and the Company estimates the useful life of the asset and begins amortization. The Company periodically assesses whether triggering events are present to review internal-use software for impairment. Changes in estimates related to internal-use software would increase or decrease operating expenses or amortization recorded during the reporting period. ​ The Company amortizes its internal-use software over the estimated useful lives of three years. The net book value of capitalized software held for internal use was $1.7 million and $1.2 million as of December 31, 2020 and 2019, respectively. Amortized expense for amounts previously capitalized for the years ended December 31, 2020, 2019, and 2018 was $1.0 million, $1.2 million, and $1.3 million, respectively. ​ Accumulated Other Comprehensive Income (Loss) Comprehensive loss and its components encompass all changes in equity other than those with stockholders, and include net loss, unrealized gains and losses on available-for-sale marketable securities. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ ​ 2020 ​ 2019 ​ ​ (in thousands) Beginning balance ​ $ 919 ​ $ (552) Net unrealized gains on available-for-sale securities, net of tax ​ ​ 3,340 ​ ​ 1,471 Ending balance ​ $ 4,259 ​ $ 919 ​ ​ ​ ​ ​ ​ ​ ​ Property and Equipment ​ Property and equipment, including purchased and internally developed software, are stated at cost. Depreciation is calculated using the straight-line method over the estimated useful lives of the assets, which are generally three five ​ Impairment of Long-lived Assets ​ The Company evaluates its long-lived assets for indicators of possible impairment when events or changes in circumstances indicate the carrying amount of an asset may not be recoverable. The Company then compares the carrying amounts of the assets with the future net undiscounted cash flows expected to be generated by such asset. Should an impairment exist, the impairment loss would be measured based on the excess carrying value of the asset over the asset’s fair value determined using discounted estimates of future cash flows. ​ Inventory ​ Inventory is valued at the lower of the standard cost, which approximates actual cost, or market. Cost is determined using the first-in, first-out ("FIFO") method. Inventory consists entirely of supplies, which are consumed when providing its test reports, and therefore does not maintain any finished goods inventory. The Company enters into inventory purchases and commitments so that it can meet future delivery schedules based on forecasted demand for its tests. ​ The Company recorded inventory obsolescence charges totaling $0.2 million, $0.3 million, and $0.3 million in the years ended December 31, 2020, 2019, and 2018, respectively. ​ Recent Accounting Pronouncements ​ From time to time, new accounting pronouncements are issued by the Financial Accounting Standards Board (the “FASB”) under its accounting standard codifications (“ASC”) or other standard setting bodies and adopted by the Company as of the specified effective date. Unless otherwise discussed below, the Company believes that the impact of recently issued standards that are not yet effective will not have a material impact on its financial position or results of operations upon adoption. ​ Recently Adopted Accounting Pronouncements ​ Fair Value Measurement In August 2018, the FASB issued ASU 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement Goodwill - Internal-Use Software In August 2018, the FASB issued ASU 2018-15, Intangibles-Goodwill and Other-Internal-Use Software (Subtopic 350-40): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract Credit Losses In June 2016, the FASB issued ASU 2016-13, Financial Instruments—Credit Losses: Measurement of Credit Losses on Financial Instruments 2019-04, and ASU 2019-05. The standard requires measurement and recognition of expected credit losses for financial assets by requiring an allowance to be recorded as an offset to the amortized cost of such assets. For available-for-sale debt securities, expected credit losses should be estimated when the fair value of the debt securities is below their associated amortized costs. The Company adopted ASU 2016-13, as amended, effective January 1, 2020 using the modified retrospective method and recorded a cumulative-effect adjustment of $0.4 million in accumulated deficit as of January 1, 2020. Collaborative Arrangements In November 2018, the FASB issued ASU 2018-18, Collaborative Arrangements (Topic 808): Clarifying the Interaction between Topic 808 and Topic 606 Income Taxes In December 2019, the FASB issued ASU 2019-12, Simplifying the Accounting for Income Taxes (Topic 740), which simplifies the accounting for income taxes, eliminates certain exceptions within ASC 740, Income Taxes, and clarifies certain aspects of the current guidance to promote consistency among reporting entities. ASU 2019-12 is effective for fiscal years beginning after December 15, 2020. An entity that elects early adoption must adopt all the amendments in the same period. Most amendments within this ASU are required to be applied on a prospective basis, while certain amendments must be applied on a retrospective or modified retrospective basis. The Company has adopted this standard as of September 30, 2020, which did not have a material impact on its consolidated financial statements upon the adoption. New Accounting Pronouncements Not Yet Adopted ​ In March 2020, ASU 2020-04, Reference Rate Reform (Topic 848) In August 2020, ASU 2020-06, Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging—Contracts in Entity’s Own Equity (Subtopic 815-40) In October 2020, ASU 2020-10, Codification Improvements comprehensive income. ASU 2010-10 is effective for fiscal years beginning after December 15, 2020, including interim periods within those fiscal years. Early application of the amendments is permitted for public business entities for any annual or interim period for which financial statements have not been issued. The Company is currently evaluating the impact of the adoption of this standard on its consolidated financial statements.

Revenue Recognition

Revenue Recognition	12 Months Ended
	Dec. 31, 2020
Revenue Recognition
Revenue Recognition	3. Revenue Recognition ​ ​ Product Revenues ​ Product revenues are derived from contracts with insurance carriers, laboratory partners and patients in connection with sales of prenatal genetic and other diagnostics tests. The Company enters into contracts with insurance carriers with primarily payment terms related to tests provided to the patients who have health insurance coverage. Insurance carriers are considered as third-party payers on behalf of the patients, and the patients are considered as the customers who receive genetic test services. Tests may be billed to insurance carriers, patients, or a combination of insurance carriers and patients. Further, the Company sells tests to a number of domestic and international laboratory partners and identifies the laboratory partners as customers provided that there is a test services agreement between the two parties. ​ A performance obligation represents a promise in a contract to transfer a distinct good or service to a customer, which represents a unit of accounting in accordance with ASC 606. A performance obligation is considered distinct from other obligations in a contract when it provides a benefit to the customer either on its own or together with other resources that are readily available to the customer and is separately identified in the contract. The Company considers a performance obligation satisfied once the Company has transferred control of a good or service to the customer, meaning the customer has the ability to use and obtain the benefit of the good or service. A portion of the consideration should be allocated to each distinct performance obligation and recognized as revenue when, or as, the performance obligation is satisfied. The Company evaluates its contracts with insurance carriers, laboratory partners and patients and identifies the performance obligations in those contracts, which are the delivery of the test results. ​ The total consideration which the Company expects to collect in exchange for the Company’s products is an estimate and may be fixed or variable. Consideration includes reimbursement from both patients and insurance carriers, adjusted for variable consideration related to disallowed cases, discounts, refunds and doubtful accounts, and is estimated using the expected value approach. For insurance carriers with similar reimbursement characteristics, the Company uses a portfolio of relevant historical data to estimate variable consideration and total collections for the Company’s products. The Company constrains the estimated variable consideration when it assesses it is probable that a significant reversal in the amount of cumulative revenue recognized may occur in future periods. The consideration expected from laboratory partners usually includes a fixed amount, but it can be variable depending on the volume of tests performed, and the Company determines the variable consideration using the expected value approach. For insurance carriers, laboratory partners and patients, the Company allocates the total consideration to a single performance obligation, which is the delivery of the test results to the customers. ​ When assessing the total consideration for insurance carriers and patients, a certain percentage of revenues is further constrained for estimated refunds. ​ The Company generally bills an insurance carrier, a laboratory partner or a patient upon delivery of test results. The Company also bills patients directly for out-of-pocket costs involving co-pays and deductibles that they are responsible for. Tests billed to insurance carriers and directly to patients usually take an average of nine to twelve months to collect payment, and for tests billed to laboratory distribution partners, the average collection cycle takes approximately two to three months. At times, the Company may or may not get reimbursed for the full amount billed. Further, the Company may not get reimbursed at all for tests performed if such tests are not covered under the insurance carrier’s reimbursement policies or the Company is not a qualified provider to the insurance carrier, or if the tests were not previously authorized. Product revenue is recognized in an amount that equals to the total consideration (as described above) at a point in time when the test results are delivered. The Company reserves certain amounts in other accrued liabilities on the balance sheet in anticipation of requests for refunds of payments previously made by insurance carriers, which are accounted for as reductions in product revenues in the statement of operations and comprehensive loss. During the years ended December 31, 2020, 2019, and 2018, $5.4 million, $2.4 million, and $3.3 million, respectively, were released from amounts previously held in reserves in other accrued liabilities and recognized as product revenue. ​ Licensing and Other Revenues ​ The Company recognizes licensing revenues from its cloud-based distribution service offering, Constellation, by granting licenses to its licensees to use certain of the Company’s proprietary intellectual properties and cloud-based software and IVD kits. The Company also recognizes revenues from the Signatera research use only (“RUO”) offering, the Qiagen LLC, BGI Genomics Co., Ltd., and Foundation Medicine, Inc. agreements. Constellation The laboratory partners with which the Company enters into a licensing arrangement represent the licensees and are identified as customers. The licensees do not have the right to possess the Company’s software, but rather receive professional services through the cloud software. These arrangements often include: (i) the delivery of the services through the cloud software, (ii) the necessary support and training, and (iii) the IVD kits to be consumed as tests are processed. The Company does not consider the software as a service, the support and training as being distinct in the context of such arrangements, and therefore they are combined as a single performance obligation. The software, support and training are delivered simultaneously to the licensees over the term of the arrangement. The Company bills the majority of licensees, who process the tests in their laboratories, a fixed price for each test processed. Licensing revenues are recognized as the performance obligations are satisfied (i.e., upon the delivery of each test) and reported in licensing and other revenues in the statements of operations and comprehensive loss. ​ Signatera Qiagen In March 2018, the Company entered into a License, Development and Distribution Agreement (“the Qiagen Agreement”) with Qiagen under which the Company granted Qiagen a license to develop, manufacture, distribute and commercialize NGS-based genetic testing assays and sequencing systems utilizing such assays, which incorporate the Company’s proprietary technology. According to the terms of the agreement, the Company is initially entitled to receive an upfront license fee and prepaid royalties totaling $40.0 million, which was fully collected in 2018. All or a portion of the prepaid royalties are refundable in limited circumstances. In addition, the Company was entitled to potential milestone payments from Qiagen upon the successful achievement of certain volume, regulatory and commercial milestones, and tiered royalties of $10.0 million, of which the Company received $5.0 million due December 31, 2018. The Qiagen Agreement has a term of 10 years and expires in March 2028, and it may be terminated earlier in certain circumstances. Upon termination of the Qiagen Agreement, the license granted to Qiagen will also terminate, except in certain limited circumstances. The Company provided to Qiagen standard indemnification protections, which is part of an assurance that the license meets the contract’s specifications and is not an obligation to provide goods or services. In October 2019, Qiagen announced that it had discontinued the development of its next generation sequencing platform and is now partnered with another supplier to develop next generation sequencing based tests. The Company subsequently notified Qiagen of its material breach of the Qiagen Agreement. Effective in March 2020, the Company terminated the Qiagen Agreement, and all or a portion of the prepaid royalties are refundable in limited circumstances, including upon termination in certain circumstances. The parties are currently in discussions regarding their respective obligations resulting from the termination of the Qiagen Agreement. Because the amount of prepaid royalty subject to refund is not finalized, the refund amount, if any, is uncertain as of December 31, 2020. As a result, this variable consideration was not included in the transaction price in 2020 to mitigate the risk of significant reversal of the cumulative revenue in the subsequent periods. Accordingly, no revenues were recognized on the prepaid royalties which may be subject to a refund. BGI Genomics In February 2019, the Company entered into a License Agreement with BGI Genomics Co., Ltd. (“BGI Genomics”) to develop, manufacture, and commercialize NGS-based genetic testing assays for clinical and commercial use. The agreement has a term of ten years and expires in February 2029. According to the agreement, the Company is entitled to a total of $50 million, comprised of upfront technology license fees, prepaid royalties relating to future sales of licensed products and performance of assay interpretation services, and milestone payments. During the three months ended June 30, 2019, the Company received $35.6 million, net of withholding taxes, of these amounts. The Company recorded a receivable of $2.5 million upon achieving the first milestone as of June 30, 2019, which was received in January 2021. Also, as required by the agreement with BGI Genomics, in June 2019 the Company prepaid $6.0 million to BGI Genomics for future sequencing services and $4.0 million for future sequencing equipment. These advance payments for equipment and services to be received in future periods aggregating to $10.0 million were recorded in long-term advances on the Balance Sheet. ​ Pursuant to the agreement, the Company licensed its intellectual property and will provide development services. Following completion of development services, the Company will provide assay interpretation services over the term of the agreement. The Company concluded that the license is not a distinct performance obligation as it does not have a stand-alone value to BGI Genomics apart from the related development services. Therefore, license and related development services, for each of NIPT and Oncology products, represents a single performance obligation. ​ The Company is responsible for granting a license to specified intellectual property and performing certain development activities to customize its genetic testing assays for oncology and NIPT for use with BGI Genomics’ sequencing instruments and proprietary technology platform. Revenue associated with these performance obligations is recognized over time using the input method, based on costs incurred to perform the development services, since the level of costs incurred over time best reflect the transfer of development services. Revenue associated with the assay interpretation services will be recognized upon delivery of these services. Funds received in advance are recorded as deferred revenue and will be recognized as the related services are delivered. The initial transaction price was primarily comprised of license and milestone fees. The Company constrains the estimated variable consideration when it assesses it is probable that a significant reversal in the amount of cumulative revenue recognized may occur in future periods. Certain milestone and license fees were constrained and not included in the transaction price due to the uncertainties of research and development. The Company re-evaluates the transaction price, including the estimated variable consideration included in the transaction price and all constrained amounts, in each reporting period and as uncertain events are resolved or other changes in circumstances occur. The allocation of the transaction price was performed based on standalone selling prices, which are based on estimated amounts that the Company would charge for a performance obligation if it were sold separately. In accordance with ASC 340-40, any incremental costs incurred to obtain a contract with a customer are required to be capitalized and amortized over the period in which the goods and services are transferred to the customer. The Company has elected to apply a practical expedient under ASC 340-40 to recognize the incremental costs of obtaining a contract as an expense when incurred provided that the amortization period of such costs, if capitalized, is one year or less. The incremental costs incurred in connection with the BGI Genomics arrangement is not material on an accumulated basis and therefore will not be capitalized on the balance sheet but will be expensed as incurred. ​ Foundation Medicine, Inc. In August 2019, the Company entered into a License and Collaboration Agreement (“the Foundation Medicine Agreement”) with Foundation Medicine, Inc. (“Foundation Medicine”) to develop and commercialize personalized circulating tumor DNA monitoring assays, for use by biopharmaceutical and clinical customers who order Foundation Medicine’s FoundationOne CDx. The agreement has an initial term of five years , expiring in August 2024, with automatic renewals thereafter for successive one-year terms, unless the agreement is earlier terminated in accordance with its terms. Natera and Foundation Medicine will share the revenues generated from both biopharmaceutical and clinical customers in accordance with the terms of the agreement. The agreement provides for approximately $13.3 million in upfront licensing fees and prepaid revenues payable to the Company, and up to approximately $32.0 million in minimum annual payments and payments tied to the Company’s achievement of certain developmental, regulatory, and commercial milestones. As of December 31, 2019, the Company received $16.3 million of these amounts, of which $3.0 million was for achieving certain milestones, and $13.3 million was for licensing fees and prepaid revenue. No additional payments have been received in the year ending December 31, 2020. ​ Pursuant to the agreement, the Company will provide development services in conjunction with granting the use of the Company’s intellectual property. Following completion of those development services, the Company will provide assay testing services over the term of the agreement. The Company has concluded that the license is not a distinct performance obligation as it is highly interrelated and interdependent with the related development services. Therefore, license and related development services represent a single performance obligation. ​ The Company is responsible for providing the technology license and certain development services that are required to customize its proprietary Signatera test to work with Foundation Medicine’s FoundationOne CDx. The intellectual property has been licensed to Foundation Medicine for the customized test. In addition, the Company is responsible for delivering clinical study plans in order to demonstrate efficacy of the customized test. Revenues associated with each of the performance obligations are recognized over time using the input method, based on costs incurred to perform the development services, since the level of costs incurred over time best reflect the transfer of development services. Revenue associated with the assay testing services will be recognized upon delivery of these services. Funds received in advance are recorded as deferred revenue and will be recognized as the related services are delivered. ​ The initial transaction price was primarily comprised of license and milestone fees. The Company constrains the estimated variable consideration when it assesses it is probable that a significant reversal in the amount of cumulative revenue recognized may occur in future periods. Certain milestone fees were constrained and not included in the transaction price due to the uncertainties of research and development. The Company re-evaluates the transaction price, including the estimated variable consideration included in the transaction price and all constrained amounts, in each reporting period and as uncertain events are resolved or other changes in circumstances occur. The allocation of the transaction price was performed based on standalone selling prices, which are based on estimated amounts that the Company would charge for a performance obligation if it were sold separately. ​ In accordance with ASC 340-40, any incremental costs incurred to obtain a contract with a customer are required to be capitalized and amortized over the period in which the goods and services are transferred to the customer. The Company has elected to apply a practical expedient under ASC 340-40 to recognize the incremental costs of obtaining a contract as an expense when incurred provided that the amortization period of such costs, if capitalized, is one year or less. Disaggregation of Revenues ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, ​ ​ 2020 ​ 2019 ​ 2018 ​ ​ (in thousands) Insurance carriers ​ $ 300,220 ​ $ 210,919 ​ $ 193,895 Laboratory partners ​ ​ 58,196 ​ ​ 59,876 ​ ​ 44,062 Patients ​ ​ 32,589 ​ ​ 31,533 ​ ​ 19,697 Total revenues ​ $ 391,005 ​ $ 302,328 ​ $ 257,654 ​ The following table presents total revenues by geographic area based on the location of the Company’s payers: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year ended December 31, ​ ​ 2020 2019 2018 ​ ​ (in thousands) United States ​ $ 365,660 $ 260,846 $ 225,931 Americas, excluding U.S. ​ ​ 3,469 ​ 3,218 ​ 3,472 Europe, Middle East, India, Africa ​ ​ 14,332 ​ 15,434 ​ 20,866 Asia Pacific and Other ​ ​ 7,544 ​ 22,830 ​ 7,385 Total ​ $ 391,005 $ 302,328 ​ $ 257,654 ​ The following table summarizes the Company’s beginning and ending balances of accounts receivable and deferred revenues: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Balance at ​ Balance at ​ ​ December 31, ​ December 31, ​ ​ 2020 ​ 2019 ​ ​ (in thousands) Assets: ​ ​ ​ ​ ​ ​ Accounts receivable ​ $ 78,565 ​ $ 53,351 Liabilities: ​ ​ ​ ​ ​ ​ Deferred revenue, current portion ​ $ 50,125 ​ $ 56,016 Deferred revenue, long-term portion ​ ​ 22,805 ​ ​ 23,808 Total deferred revenues ​ $ 72,930 ​ $ 79,824 ​ ​ ​ ​ ​ ​ ​ ​ Deferred ​ ​ Revenues ​ ​ (in thousands) Balance at December 31, 2019 ​ $ 79,824 Increase in deferred revenues ​ ​ 2,397 Reclasses from deferred revenues to other to short-term liabilities ​ ​ (799) Revenue recognized during the period that was included in ​ ​ (7,246) Revenue recognized from performance obligations satisfied ​ ​ (1,246) Balance at December 31, 2020 ​ $ 72,930 ​ During the year ended December 31, 2020, revenue recognized that was included in the deferred revenue balance at the beginning of the period totaled $7.2 million with approximately $6.8 million related to BGI Genomics and Foundation Medicine, and the remaining $0.4 million related to genetic testing services. During the year ended December 31, 2020, $1.2 million was recognized as deferred revenue and later earned as revenue in the same period. The current portion of deferred revenue includes $3.9 million from the BGI Genomics agreement and $6.2 million from the Foundation Medicine agreement.

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2020
Fair Value Measurements
Fair Value Measurements	4. Fair Value Measurements ​ The Company's financial assets and liabilities carried at fair value are comprised of investment assets that include money market and investments, and a liability for common stock warrants. ​ The fair value accounting guidance requires that assets and liabilities be carried at fair value and classified in one of the following three categories: ​ Level I: Quoted prices in active markets for identical assets and liabilities that the Company has the ability to access. ​ Level II: Observable market-based inputs or unobservable inputs that are corroborated by market data, such as quoted prices, interest rates, and yield curves. ​ Level III: Inputs that are unobservable data points that are not corroborated by market data. ​ This hierarchy requires the Company to use observable market data, when available, and to minimize the use of unobservable inputs when determining fair value. ​ Assets and Liabilities That Are Measured at Fair Value on a Recurring Basis ​ The following table represents the fair value hierarchy for the Company’s financial assets and financial liabilities measured at fair value on a recurring basis: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2020 ​ December 31, 2019 ​ Level I Level II Level III Total Level I Level II Level III Total ​ ​ (in thousands) Financial Assets: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Money market deposits ​ $ 28,990 ​ ​ — ​ $ — ​ $ 28,990 ​ $ 22,477 ​ $ — ​ $ — ​ $ 22,477 ​ U.S. Treasury securities ​ ​ 597,744 ​ ​ — ​ ​ — ​ ​ 597,744 ​ ​ 293,157 ​ ​ — ​ ​ — ​ ​ 293,157 ​ Corporate bonds and notes ​ ​ — ​ ​ 12,328 ​ ​ — ​ ​ 12,328 ​ ​ — ​ ​ — ​ ​ — ​ ​ — ​ Municipal securities ​ ​ — ​ ​ 78,534 ​ ​ — ​ ​ 78,534 ​ ​ — ​ ​ 85,908 ​ ​ — ​ ​ 85,908 ​ Total financial assets ​ $ 626,734 ​ $ 90,862 ​ $ — ​ $ 717,596 ​ $ 315,634 ​ $ 85,908 ​ $ — ​ $ 401,542 ​ ​ During the year ended December 31, 2020, the Company did not make any transfers between Level I and Level II assets.

Financial Instruments

Financial Instruments	12 Months Ended
	Dec. 31, 2020
Financial Instruments
Financial Instruments	5. Financial Instruments ​ The Company elected to invest a portion of its cash assets in conservative, income earning, liquid investments. Cash equivalents and investments, all of which are classified as available-for-sale securities, consisted of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2020 ​ December 31, 2019 ​ Amortized Gross Gross Estimated Fair Amortized Gross Gross Estimated Fair ​ ​ (in thousands) Money market deposits ​ $ 28,990 ​ $ — ​ $ — ​ $ 28,990 ​ $ 22,477 ​ $ — ​ $ — ​ $ 22,477 ​ U.S. Treasury securities (1) ​ 594,252 ​ 3,512 ​ (20) ​ 597,744 ​ 292,506 ​ 731 ​ (80) ​ 293,157 ​ Corporate bonds and notes (1) ​ 12,331 ​ 2 ​ (5) ​ 12,328 ​ — ​ — ​ — ​ — ​ Municipal securities ​ ​ 77,764 ​ ​ 796 ​ ​ (26) ​ ​ 78,534 ​ ​ 85,638 ​ ​ 277 ​ ​ (7) ​ ​ 85,908 ​ Total ​ $ 713,337 ​ $ 4,310 ​ $ (51) ​ $ 717,596 ​ $ 400,621 ​ $ 1,008 ​ $ (87) ​ $ 401,542 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Classified as: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Cash equivalents (2) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ $ 28,990 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ $ 22,477 ​ Short-term investments ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 688,606 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 379,065 ​ Total ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ $ 717,596 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ $ 401,542 ​ ​ (1) Per the Company’s investment policy, all U.S. Treasury securities, corporate bonds and notes are classified as short-term investments irrespective of holding period. (2) Cash equivalents includes cash sweep accounts and U.S. Treasury money market mutual funds. ​ The Company invests in U.S. Treasuries, U.S. agency and high quality municipal bonds which mature at par value and are all paying their coupons on schedule. The Company has therefore concluded there is currently no other than temporary impairment of its investments and will continue to recognize unrealized gains and losses in other comprehensive income (loss). During the year ended December 31, 2020, the Company sold $30.1 million of investments. There were no sales of investments during the year ended December 31, 2019. During the year ended December 31, 2020, the amount of gross realized gains and realized losses upon sales of investments were insignificant. The Company uses the specific investment identification method to calculate realized gains and losses and amounts reclassified out of other comprehensive income to net income. As of December 31, 2020, the Company had 13 investments in an unrealized loss position in its portfolio. An allowance for credit losses was not necessary since the fair market value for a majority of the available-for-sale securities increased as a result of a significant average yield rate decrease for similar securities as of December 31, 2020. ​ In accordance with the adoption of ASU 2016-13 (Topic 326), the Company has assessed the unrealized loss position for available-for-sale debt securities for which an allowance for credit losses has not been recorded. The fair value for investment securities at an unrealized loss position as of December 31, 2020 was $144.0 million. The aggregate amount of unrealized losses of these securities were not significant, and the impact of the securities in a continuous loss position to the consolidated statements of operations and comprehensive loss were not material as of December 31, 2020. ​ The following table summarizes the Company’s portfolio of available-for-sale securities by contractual maturity as of December 31, 2020: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2020 ​ ​ ​ Amortized ​ Fair ​ ​ ​ (in thousands) ​ Less than or equal to one year ​ $ 322,416 ​ $ 323,002 ​ Greater than one year but less than five years ​ ​ 361,931 ​ ​ 365,604 ​ Total ​ $ 684,347 ​ $ 688,606 ​ ​

Balance Sheet Components

Balance Sheet Components	12 Months Ended
	Dec. 31, 2020
Balance Sheet Components
Balance Sheet Components	6. Balance Sheet Components ​ Credit Losses ​ The following is a roll-forward of the allowances for credit losses related to trade accounts receivable and other receivables for the years ended December 31, 2020, 2019, and 2018: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ December 31, ​ December 31, ​ 2020 ​ 2019 ​ 2018 ​ (in thousands) Beginning balance $ 2,919 ​ $ 1,788 ​ $ 2,000 Cumulative-effect adjustment upon adoption of ASU 2016-13 ​ 404 ​ ​ — ​ ​ — Provision for credit losses ​ 1,354 ​ ​ 1,141 ​ ​ (41) Write offs ​ (457) ​ ​ (10) ​ ​ (171) Ending balance $ 4,220 ​ $ 2,919 ​ $ 1,788 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Property and Equipment, net ​ The Company’s property and equipment consisted of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ December 31, ​ ​ Useful Life 2020 2019 ​ ​ ​ ​ ​ (in thousands) ​ Machinery and equipment 3-5 years $ 51,001 ​ $ 36,414 ​ Furniture and fixtures 3 years ​ 1,376 ​ 1,376 ​ Computer equipment 3 years ​ 2,428 ​ 1,828 ​ Capitalized software held for internal use ​ 3 years ​ ​ 7,417 ​ ​ 5,917 ​ Leasehold improvements Life of lease ​ 14,810 ​ 11,556 ​ Construction-in-process ​ ​ ​ 6,370 ​ 7,716 ​ ​ ​ ​ ​ 83,402 ​ 64,807 ​ Less: Accumulated depreciation and amortization ​ ​ ​ (50,054) ​ (41,524) ​ Total Property and Equipment, net ​ ​ ​ $ 33,348 ​ $ 23,283 ​ ​ All of the Company’s long-lived assets are located in the United States. Other Assets ​ Debt Debt ​ Accrued Compensation ​ The Company’s accrued compensation consisted of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, December 31, ​ ​ 2020 2019 ​ ​ (in thousands) ​ Accrued paid time off ​ $ 2,260 ​ $ 1,850 ​ Accrued commissions ​ 12,686 ​ 5,767 ​ Accrued bonuses ​ 9,635 ​ 5,710 ​ Other accrued compensation ​ 5,790 ​ 2,761 ​ Total accrued compensation ​ $ 30,371 ​ $ 16,088 ​ ​ ​ ​ Other Accrued Liabilities ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, December 31, ​ 2020 2019 ​ ​ (in thousands) Reserves for refunds to insurance carriers ​ $ 17,366 ​ $ 9,410 ​ Accrued charges for third-party testing ​ ​ 5,141 ​ ​ 8,408 ​ Testing and laboratory materials from suppliers ​ ​ 2,720 ​ ​ 4,301 ​ Marketing and corporate affairs ​ ​ 3,325 ​ ​ 2,957 ​ Legal, audit and consulting fees ​ ​ 4,189 ​ ​ 2,873 ​ Accrued shipping charges ​ ​ 1,604 ​ ​ 305 ​ Sales tax payable ​ ​ 1,723 ​ ​ 1,691 ​ Accrued specimen service fees ​ ​ 2,355 ​ ​ 2,269 ​ Clinical trials and studies ​ 2,353 ​ 1,092 ​ Operating lease liabilities, current portion ​ ​ 7,300 ​ ​ 5,739 ​ Fixed asset purchases ​ ​ 1,691 ​ ​ 1,482 ​ Other accrued interest ​ ​ 1,078 ​ ​ — ​ Other accrued expenses ​ 9,562 ​ 8,516 ​ Total other accrued liabilities ​ $ 60,407 ​ $ 49,043 ​ ​ Reserves for refunds to insurance carriers include overpayments from and amounts to be refunded to insurance carriers, and additional amounts that the Company estimates for potential refund requests during the period. When the Company releases these previously accrued amounts, they are recognized as product revenues in the statements of operations and comprehensive loss. ​ The following table summarizes the reserve balance and activities for refunds to insurance carriers for the year ended December 31, 2020: ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, December 31, ​ 2020 2019 ​ ​ (in thousands) Beginning balance ​ $ 9,410 ​ $ 10,012 Additional reserves ​ ​ 19,427 ​ ​ 9,560 Refunds to carriers ​ ​ (6,066) ​ ​ (7,752) Reserves released to revenue ​ ​ (5,405) ​ ​ (2,410) Ending balance ​ $ 17,366 ​ $ 9,410 ​

Leases

Leases	12 Months Ended
	Dec. 31, 2020
Leases
Leases	7. Leases ​ Operating Leases ​ In September 2015, the Company’s subsidiary entered into a long-term lease agreement for laboratory and office space totaling approximately 94,000 square feet in Austin, Texas. The lease term is 132 months beginning in December 2015 and expiring in November 2026 with monthly payments beginning in December 2016. In October 2016, the Company entered into a lease directly with its landlord for laboratory and office spaces at its facilities located in San Carlos, California. The Company currently occupies approximately 113,000 square feet comprised of two office spaces (the “First Space” and the “Second Space”). The First Space covers approximately 88,000 square feet, and the Second Space totals approximately 25,000 square feet. The term of this lease is approximately 84 months and expires in October 2023. This lease contains an option to renew the lease term for five years, but the fair market rent amount upon renewal is not available from the landlord. In January 2021, the Company entered into an amendment of the lease to extend the term for 48 months to October 2027. The combined annual rent for the First Space and Second Space will be $9.3 million commencing in October 2023. The Company entered into a lease agreement commencing June 2018 for its cord blood tissue storage facility in Tukwila, Washington that covers approximately 10,000 square feet. The lease term is 62 months expiring in July 2023. The Company has the option to extend this lease for five years, and the fair market rent upon renewal is not determinable. However, since the Company sold its business related to cord blood and tissue storage in September 2019, the Company has subleased the facility and does not intend to exercise its option to renew the facility upon expiration. In addition, the Company entered into a sublease agreement in June 2019 with a third party to sublease 25,879 square feet of space located on the third floor of the San Carlos, California building while maintaining its primary obligation as the intermediate lessor. The term of this lease is approximately 48 months commencing in October 2019 and expiring in September 2023. The annual lease payment starts at $1.9 million and will escalate annually commencing in October 2020. In February 2021, the Company entered into an amendment of the San Carlos sublease agreement whereas the third party will initially return approximately 3,474 rentable square feet with the remainder of the subleased premises, consisting of approximately 22,405 rentable square feet, between October 2021 and December 2021. The Company entered into a lease agreement in November 2020 to lease 11,395 square feet of space located in South San Francisco, California over a 36-month The Company has also entered into leases of individual workspaces at premises located in different locations on a month-to-month basis and is not committed to an established lease term. The Company has elected to not recognize them as the right-of-use assets on the balance sheet as they are all considered as short-term leases. Expenses associated with short-term lease were not significant for the year ended December 31, 2020. ​ ​ ​ ​ ​ ​ ​ December 31, ​ ​ 2020 ​ ​ (in thousands) Operating lease liabilities, current portion included in other accrued liabilities ​ $ 7,300 Operating lease liabilities, long-term portion ​ ​ 21,246 Total operating lease liabilities ​ $ 28,546 ​ The initial recognition of the operating lease liabilities was measured as the present value of the future minimum lease payments using a discount rate determined as of January 1, 2019. The operating right-of-use assets was calculated as the operating lease liabilities discounted at the present value, less the amount of unamortized tenant improvement allowance and deferred rent. The discount rate used was the Company’s incremental borrowing rate given that the implicit rate to each lease was not readily determinable. In accordance with ASC 842, the incremental borrowing rate was estimated as the annual percentage yield resulting from a corporate debt financing over a loan term approximating the remaining term of each lease, with the effect of certain credit risk rating. For the year ended December 31, 2020, we had noncash investing activities of $2.4 million related to right-of-use assets. As of December 31, 2020, the weighted-average remaining lease term was 2.28 The Company continues to recognize lease expense on a straight-line basis. The lease expense includes the amortization of the right-of-assets with the associated interest component estimated by applying the effective interest method. Total lease expense recognized in the statements of operations and comprehensive loss were $7.8 million, $7.8 million, and $7.4 million for the years ended December 31, 2020, 2019 and 2018. Cash paid for amounts in the measurement of operating lease liabilities totaled $9.0 million, $8.6 million and $7.9 million for the years ended December 31, 2020, 2019 and 2018, respectively. The present value of the future annual minimum lease payments under all non-cancellable operating leases as of December 31, 2020 are as follows: ​ ​ ​ ​ ​ ​ ​ Operating Leases ​ ​ (in thousands) Year ending December 31: ​ ​ ​ ​ 2021 ​ $ 9,958 ​ 2022 ​ ​ 10,242 ​ 2023 ​ ​ 8,670 ​ 2024 ​ ​ 2,400 ​ 2025 ​ ​ 2,447 ​ 2026 and thereafter ​ ​ 2,283 ​ Total future minimum lease payments ​ ​ 36,000 ​ Less: imputed interest ​ ​ (7,454) ​ Operating lease liabilities ​ $ 28,546 ​ ​

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2020
Commitments and Contingencies
Commitments and Contingencies	8. Commitments and Contingencies ​ Legal Proceedings ​ From time to time, the Company is involved in disputes, litigation, and other legal actions, including those with respect to intellectual property, employment, testing and other matters. Such actions may include allegations of negligence, products/professional liability or other similar legal claims, and could involve claims for substantial compensatory and/or punitive damages or claims for indeterminate amounts of damages. The Company is aggressively defending and/or prosecuting its current litigation matters, but cannot provide any assurance as to the ultimate outcome or that an adverse resolution would not have a material adverse effect on its financial condition and results of operations. There are many uncertainties associated with any litigation and these actions or other third party claims against the Company, or by the Company against third parties, may cause the Company to incur costly litigation and/or substantial settlement charges. In addition, the resolution of any intellectual property litigation may require the Company to make royalty payments, which could adversely affect gross margins in future periods. If this were to occur, the Company's business, financial condition, results of operations, and cash flows could be adversely affected. The Company assesses legal contingencies to determine the degree of probability and range of possible loss for potential accrual in its financial statements. When evaluating legal contingencies, the Company may be unable to provide a meaningful estimate due to a number of factors, including the procedural status of the matter in question, the presence of complex or novel legal theories, and/or the ongoing discovery and development of information important to the matters. In addition, damage amounts claimed in litigation against it may be unsupported, exaggerated or unrelated to possible outcomes, and as such are not meaningful indicators of its potential liability. During the periods presented, the Company has not recorded any accrual for loss contingencies associated with such legal proceedings, determined that an unfavorable outcome is probable or reasonably possible, or determined that the amount or range of any possible loss is reasonably estimable. Intellectual Property Litigation Matters. In March 2018, Illumina, Inc., or Illumina, filed a lawsuit (the ’831 lawsuit) against the Company in the United States District Court for the Northern District of California, alleging that the Company’s Panorama test infringes certain claims of U.S. Patent No. 9,493,831 (the ’831 patent) and seeking, among other relief, damages or other monetary relief including costs and pre- and post-judgment interest, treble damages, injunctive relief, attorneys’ fees and costs. In August 2018, the Company filed a counterclaim against Illumina, alleging that certain of Illumina’s NIPT tests infringe on the Company’s U.S. Patent No. 8,682,592 (the ’592 patent) and seeking, among other relief, damages or other monetary relief including costs and pre- and post-judgment interest, treble damages, injunctive relief, attorneys’ fees and costs (together with the ‘831 lawsuit, the “Illumina Litigation”). In May 2020, the parties settled the Illumina Litigation pursuant to which all claims in the Illumina Litigation, including compulsory counterclaims, relating to NIPT and PGS/PGD activities occurring before the date of such settlement were resolved and dismissed. Separately, on December 11, 2020, the United States Patent and Trademark Office issued a final written decision affirming the validity of all claims challenged by Illumina in its inter partes ​ The Company is involved in patent litigation against CareDx, Inc., or CareDx, in the United States District Court for the District of Delaware (“CareDx’s Patent Case”). CareDx alleges, in a complaint filed on March 26, 2019 and amended on March 23, 2020, that the Company infringed three patents. The complaint seeks unspecified damages and injunctive relief. The Company has also alleged that CareDx infringes two of Natera’s patents, seeking unspecified damages and injunctive relief. The Court has set a trial date of April 25, 2022. Natera is also opposing a European patent held by CareDx, with oral proceedings scheduled for May 11, 2021. ​ The Company is also the subject of a lawsuit filed by CareDx against the Company on April 10, 2019 in the United States District Court for the District of Delaware, alleging false advertising, trademark disparagement, unfair competition, and unfair or deceptive trade practices based on statements describing studies that concern the Company’s technology and CareDx’s technology (“CareDx’s Advertising Case”). The complaint seeks unspecified damages and injunctive relief. On May 30, 2019, the Company filed a motion to dismiss the entirety of CareDx’s Advertising Case for failure to state a claim. On February 7, 2020, CareDx filed an amended complaint withdrawing its trademark disparagement claim. On February 18, 2020, the Company filed a counterclaim against CareDx in the United States District Court for the District of Delaware, alleging false advertising, unfair competition and deceptive trade practices and seeking unspecified damages and injunctive relief. On December 2, 2020 the parties cross-moved for partial summary judgment. The Company has filed suit against ArcherDX, Inc., or ArcherDX, in the United States District Court for the District of Delaware, alleging, in complaints filed on January 27, 2020, April 15, 2020 and August 6, 2020, that certain ArcherDX DNA oncology products infringe four of Natera’s patents. Natera is seeking monetary damages and injunctive relief. On June 4, 2020, ArcherDX filed a motion to dismiss aspects of the Company’s case, including to invalidate several of Natera’s asserted patents. That motion was denied in its entirety on October 2, 2020. The cases were consolidated on September 25, 2020. On January 12, 2021, Company filed a second amended complaint naming an additional Archer DX entity, ArcherDx LLC, and Invitae Corp. as defendants. The second amended complaint seeks unspecified monetary damages and injunctive relief. The Company is the subject of a lawsuit filed against it by Ravgen, Inc. on June 1, 2020 in the United States District Court for the Western District of Texas, alleging infringement of two Ravgen patents. The complaint seeks monetary damages and injunctive relief. Trial is tentatively set for December 13, 2021. The Company filed suit against Progenity, Inc., or Progenity, in the United States District Court for the Western District of Texas on June 17, 2020 and in the United States District Court for the Northern District of Texas on June 19, 2020, in each case alleging that Progenity’s NIPT test infringes six of Natera’s patents. The complaints seek treble damages and injunctive relief. On or about July 2, 2020, Progenity filed suit against the Company in the United States District Court for the Southern District of California, seeking declaratory judgment of non-infringement of Natera’s asserted patents. Progenity has petitioned the Patent Trial and Appeal Board of the United States Patent and Trademark Office for inter partes On October 6, 2020, the Company filed suit against Genosity Inc., or Genosity, in the United States District Court for the District of Delaware, alleging that various Genosity oncology products infringe a Natera patent. The complaint seeks unspecified monetary damages and injunctive relief. ​ On January 20, 2021, the Company filed suit against Inivata, Inc. and Inivata Ltd. (collectively “Inivata”) in the United States District Court for the District of Delaware, alleging that various Inivata oncology products infringe two Natera patents. The complaint seeks unspecified monetary damages and injunctive relief. Other Litigation Matters. On or about August 13, 2019, a suit was filed against the Company in the Circuit Court of Cook County, Illinois by a patient alleging claims relating to a discordant test result and seeking monetary damages. On March 15, 2019, a purported class action lawsuit was filed against the Company in the United States District Court for the Northern District of California, alleging that the plaintiff received an unauthorized text message to her cellular telephone in violation of the Telephone Consumer Protection Act. Among other relief, the complaint sought statutory and other damages, injunctive relief, attorneys’ fees, and costs. The case was dismissed by stipulation of the parties effective November 2, 2020. ​ Director and Officer Indemnifications ​ As permitted under Delaware law, and as set forth in the Company’s Certificate of Incorporation and its Bylaws, the Company indemnifies its directors, executive officers, other officers, employees and other agents for certain events or occurrences that may arise while in such capacity. The maximum potential amount of future payments the Company could be required to make under this indemnification is unlimited; however, the Company has insurance policies that may limit its exposure and may enable it to recover a portion of any future amounts paid. Assuming the applicability of coverage, the willingness of the insurer to assume coverage, and subject to certain retention, loss limits and other policy provisions, the Company believes any obligations under this indemnification would not be material, other than an initial $2.5 million for securities related claims. However, no assurances can be given that the covering insurers will not attempt to dispute the validity, applicability, or amount of coverage without expensive litigation against these insurers, in which case the Company may incur substantial liabilities as a result of these indemnification obligations. ​ Third-Party Payer Reimbursement Audits ​ From time to time, the Company receives recoupment requests from third-party payers for alleged overpayments. The Company disagrees with the contentions of pending requests and/or has recorded an accrual when a refund is deemed to be probable and estimable for the alleged overpayments. ​ Contractual Commitments ​ The following table sets forth the material contractual commitments as of December 31, 2020 with a remaining term of at least one year: ​ ​ ​ ​ ​ Party Total Commitments Expiry Date ​ ​ (in thousands) ​ Laboratory instruments supplier $ 3,490 December 2021 Material suppliers ​ 17,280 June 2026 Application service providers ​ 39,425 January 2024 Gene sequencing reagents and kits provider ​ 135 April 2021 Software development provider ​ 4,000 December 2024 Other material suppliers ​ 11,690 Various ​ ​ 76,020 ​ ​ ​ ​ ​ ​

Stock-Based Compensation

Stock-Based Compensation	12 Months Ended
	Dec. 31, 2020
Stock-Based Compensation
Stock-Based Compensation	9. Stock-Based Compensation ​ Equity Plans ​ 2015 Equity Incentive Plan ​ General ​ Share Reserve The initial number of shares of the Company’s common stock available for issuance under the 2015 Plan was 3,451,495 shares. As of December 31, 2020, 13,988,187 shares were reserved for future issuance under the 2015 plan, which includes unissued and forfeited shares from the 2007 plan. ​ ● 3,500,000 shares; ​ ● 4% of the shares of common stock outstanding on the last business day of the prior fiscal year; or ​ ● the number of shares determined by the Company’s board of directors. ​ Stock options vest as determined by the compensation committee. In general, they will vest over a four-year period following the date of grant. Stock options expire at the time determined by the compensation committee but in no event more than ten years ​ Restricted Shares and Stock Units. ​ 2015 Employee Stock Purchase Plan ​ General ​ Share Reserve. ​ ● 880,000 shares; ​ ● 1% of the shares of common stock outstanding on the last business day of the prior fiscal year; or ​ ● the number of shares determined by the Company’s board of directors. ​ The number of shares reserved under the 2015 ESPP will automatically be adjusted in the event of a stock split, stock dividend or a reverse stock split (including an adjustment to the per-purchase period share limit). ​ Purchase Price. ​ Offering Periods. ​ The following table summarizes the offering activity during the years ended December 31, 2020 and 2019: ​ ​ ​ ​ ​ ​ ​ ​ ​ Number of ​ Total ​ ​ Shares Purchased ​ Proceeds Offering Period ​ (in thousands) November 1, 2018 - April 30, 2019 ​ 132,177 ​ $ 2,147 May 1, 2019 - October 31, 2019 ​ 136,084 ​ ​ 2,176 November 1, 2019 - April 30, 2020 ​ 97,247 ​ ​ 3,061 May 1, 2020 - October 31, 2020 ​ 136,288 ​ ​ 4,052 ​ Stock Options ​ The following table summarizes option activity during the year ended December 31, 2020: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Outstanding Options ​ ​ ​ ​ Weighted- ​ ​ ​ ​ ​ ​ ​ Weighted- ​ Average ​ ​ ​ ​ Shares ​ ​ ​ Average ​ Remaining ​ Aggregate ​ ​ Available for ​ Number of ​ Exercise ​ Contractual ​ Intrinsic ​ ​ Grant ​ Shares ​ Price ​ Life ​ Value (in thousands, except for contractual life and exercise price) ​ ​ ​ ​ ​ ​ ​ ​ (in years) ​ ​ Balance at December 31, 2019 6,416 8,497 ​ $ 10.39 6.88 ​ $ 197,955 ​ Additional shares authorized 3,120 ​ — ​ $ — ​ ​ ​ ​ ​ ​ Options granted (457) 457 ​ $ 27.67 ​ ​ ​ ​ ​ ​ Options exercised — (2,092) ​ $ 11.24 ​ ​ ​ ​ ​ ​ Options forfeited/cancelled 155 (155) ​ $ 15.39 ​ ​ ​ ​ ​ ​ RSUs granted ​ (6,204) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ RSUs forfeited/cancelled ​ 436 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Balance at December 31, 2020 3,466 6,707 ​ $ 11.19 6.04 ​ $ 592,468 ​ Exercisable at December 31, 2020 ​ ​ 5,080 ​ $ 9.04 5.40 ​ $ 459,683 ​ Vested and expected to vest at December 31, 2020 ​ ​ 6,609 ​ $ 11.09 6.01 ​ $ 584,396 ​ ​ (1) – The RSUs and options are granted under the 2015 Stock Plan. RSUs granted impact the shares available for grant pool at a 2 to 1 ratio. ​ The total intrinsic value of stock options exercised during the years ended December 31, 2020, 2019, and 2018 were $184.7 million, $70.0 million, and $25.6 million, respectively. ​ The weighted-average grant date fair value of options granted during the years ended December 31, 2020, 2019, and 2018 were $27.70, $8.01, and $4.85 per share, respectively. ​ Performance-based Awards The Company grants certain senior-level executives performance stock options and units which vest based on either market and time-based service conditions or performance and time-based service conditions, which are referred to herein as performance-based awards. The Company has assessed the performance-based award with the appropriate valuation method and has recognized the applicable stock-based compensation expense. The following table summarizes the performance-based and market-based awards as of December 31, 2020: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Period Granted ​ Options Granted ​ RSUs Granted ​ Options Vested ​ RSUs Vested ​ Milestone ​ Valuation Method (in thousands) Q1 2019 ​ 200 ​ 300 ​ 138 ​ 219 ​ (1) ​ Monte-Carlo Simulation Q2 2019 ​ — ​ 188 ​ — ​ — ​ (2) ​ Fair Market Value Q3 2019 ​ — ​ 50 ​ — ​ 25 ​ (1) ​ Monte-Carlo Simulation Q1 2020 ​ 150 ​ 300 ​ 75 ​ 150 ​ (1) ​ Monte-Carlo Simulation Q1 2020 ​ — ​ 436 ​ — ​ 4 ​ (3) ​ Fair Market Value Q1 2020 ​ 129 ​ — ​ — ​ — ​ (3) ​ Black-Scholes-Merton Q2 2020 ​ — ​ 21 ​ — ​ — ​ (3) ​ Fair Market Value Q3 2020 ​ 10 ​ — ​ 10 ​ — ​ (4) ​ Black-Scholes-Merton Q3 2020 ​ — ​ 27 ​ — ​ 5 ​ (3) ​ Fair Market Value Q4 2020 ​ — ​ 32 ​ — ​ — ​ (1) ​ Monte-Carlo Simulation Q4 2020 ​ — ​ 22 ​ — ​ — ​ (5) ​ Fair Market Value ​ (1) The awards vest based on the achievement of certain values of the Company’s common stock at multiple thresholds within certain periods and are contingent upon the completion of requisite service through the date of such vesting. (2) The vesting of the awards will be triggered after the end of the achievement milestone, as measured by the Company. (3) The awards vest based on achievement of certain revenue targets and are contingent upon the completion of requisite service through the date of such vesting. (4) The awards vest based on achievement of a reimbursement target. (5) The awards will vest based on achievement of certain revenue and recruiting targets. ​ The Company has recognized $17.2 million in stock-based compensation for performance-based awards for the year ended December 31, 2020 compared to $7.3 million in stock-based compensation for performance-based awards for the year ended December 31, 2019. ​ The fair value of the performance-based awards with market conditions granted estimated using a Monte Carlo simulation model used the following inputs for the years ended December 31, 2020 and 2019: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, December 31, ​ 2020 2019 Risk-free interest rate ​ 0.54 % — 1.64 % ​ 1.63 % — 2.61 % Expected dividend yield ​ ​ ​ ​ — ​ ​ ​ ​ ​ — ​ Expected volatility ​ 55 % — 65 % ​ ​ ​ ​ 50 % Expected term (years) ​ 5.25 ​ — 7.25 ​ ​ ​ ​ ​ 7.25 ​ ​ Restricted Stock Units ​ The following table summarizes restricted stock unit (“RSU”) activity for the year ended December 31, 2020: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted- ​ ​ ​ ​ Average ​ ​ Number of ​ Grant Date ​ ​ Shares ​ Fair Value ​ ​ (in thousands) ​ ​ ​ Balance at December 31, 2019 ​ 2,404 ​ $ 19.86 Granted ​ 3,102 ​ $ 39.94 Vested ​ (1,100) ​ $ 19.69 Canceled/Forfeited ​ (218) ​ $ 24.70 Balance at December 31, 2020 4,188 ​ $ 34.02 ​ ​ ​ ​ ​ ​ ​ ​ Stock-Based Compensation Expense ​ Stock based compensation is related to stock options and RSUs granted to the Company’s employees and is measured at the grant date based on the fair value of the award. The fair value is recognized as expense over the requisite service period, which is generally the vesting period of the respective awards on a straight-line basis. No compensation cost is recognized when the requisite service has not been met and the awards are therefore forfeited. Employee stock-based compensation expense was calculated based on awards ultimately expected to vest and has been reduced for estimated forfeitures. Forfeitures are estimated at the time of grant and revised, if necessary, in subsequent periods, if actual forfeitures differ from those estimates. Non-employee stock-based compensation expense was not adjusted for estimated forfeitures up until the occurrence of the actual forfeiture of the associated awards. ​ The following table presents the effect of employee and non-employee stock-based compensation expense on selected statements of operations line items for the years ended December 31, 2020, 2019, and 2018. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year ended December 31, ​ ​ 2020 ​ 2019 ​ 2018 ​ Employee Non-Employee Total Employee Non-Employee Total Employee Non-Employee Total ​ (in thousands) ​ Cost of revenues ​ $ 1,691 ​ $ — ​ $ 1,691 ​ $ 905 ​ $ 32 ​ $ 937 ​ $ 564 ​ $ 5 ​ $ 569 ​ Research and development ​ 10,777 ​ 647 ​ 11,424 ​ 5,354 ​ — ​ 5,354 ​ ​ 4,043 ​ — ​ 4,043 ​ Selling, general and administrative ​ 36,747 ​ 309 ​ 37,056 ​ 21,730 ​ 603 ​ 22,333 ​ ​ 9,474 ​ 112 ​ 9,586 ​ Total ​ $ 49,215 ​ $ 956 ​ $ 50,171 ​ $ 27,989 ​ $ 635 ​ $ 28,624 ​ $ 14,081 ​ $ 117 ​ $ 14,198 ​ ​ As of December 31, 2020, approximately $118.4 million of unrecognized compensation expense, adjusted for estimated forfeitures, related to unvested option awards and RSUs will be recognized over a weighted-average period of approximately 2.9 years. ​ Valuation of Stock Option Grants to Employees and Non-Employees ​ The Company utilizes Black-Scholes option pricing model when estimating the fair value of stock options. For the year ended December 31, 2020 the following valuation assumptions were applied on both the employee and non-employee options. In the same period of the prior year, the valuation assumptions as follows were only used for stock options granted to employees. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year ended December 31, ​ 2020 2019 2018 ​ Expected term (years) 5.22 ​ — 10.00 ​ ​ 5.23 ​ — 10.00 ​ ​ 5.24 ​ — 5.62 ​ Expected volatility 49.94 % — 61.96 % 42.53 % — 45.84 % ​ 40.28 % — 42.53 % Expected dividend rate ​ ​ ​ 0 % ​ ​ ​ 0 % ​ ​ ​ ​ 0 % Risk-free interest rate 0.31 % — 1.70 % 1.60 % — 2.60 % ​ 2.37 % — 3.06 % ​ As of December 31, 2020, total options outstanding include 45,577 shares of option awards that were granted to non-employees, of which 5,366 shares are unvested. Stock-based compensation expense related to stock options granted to non-employees is recognized as the stock option is earned and the services are rendered. The Company believes that the estimated fair value of the stock options is more readily measurable than the fair value of the services rendered.

Debt

Debt	12 Months Ended
	Dec. 31, 2020
Debt
Debt	10. Debt ​ Credit Line Agreement ​ In September 2015, the Company entered into a credit line with UBS (the “Credit Line”) providing for a $50.0 million revolving line of credit which can be drawn down in increments at any time. The Credit Line was amended in July 2017 and bears interest at 30-day LIBOR plus 1.10%, and it is secured by a first priority lien and security interest in the Company’s money market and marketable securities held in its managed investment account with UBS. UBS has the right to demand full or partial payment of the Credit Line Obligations and terminate the Credit Line, in its discretion and without cause, at any time. For the years ended December 31, 2020, 2019, and 2018, the Company recorded interest expense of $0.8 million, $1.7 million, and $1.6 million, respectively. Interest payments totaling $0.8 million, $1.7 million, and $1.5 million, had been made on the Credit Line during the years ended December 31, 2020, 2019, and 2018, respectively. As of December 31, 2020, remaining accrued interest was $1.1 million, and the total principal amount outstanding including accrued interest was $49.0 million. ​ 2017 Term Loan In August 2017, the Company entered into the 2017 Term Loan with OrbiMed, which has a maximum borrowing capacity of $100.0 million. On the closing date of August 8, 2017, the Company borrowed $75.0 million, with the remaining $25.0 million available to borrow at the Company’s option at any time through December 31, 2018. Subsequently, the Company entered into several amendments and extended the expiration date until December 31, 2019 to draw the unused borrowing capacity of $50.0 million. After the amendments, the interest rate was equal to the sum of (i) 8.25% plus (ii) the higher of 1.00% or LIBOR, provided the Company draw the minimum capacity of $25.0 million. If the amount drawn is less than $25.0 million, the interest rate would remain at the sum of (i) 8.75% plus (ii) the higher of 1.00% or LIBOR. As a fee in consideration of extending the commitment to provide this option to draw until December 31, 2019, the Company issued an additional 25,000 shares of our common stock to OrbiMed. As of December 31, 2019, the Company did not exercise such option, and the right to draw the unused borrowing capacity has expired. For the year ended December 31, 2020 and 2019, the Company recorded interest expense for the 2017 Term Loan totaling $2.5 million and $9.0 million, respectively, which also included the amortization of debt discount. In April 2020, the Company used a portion of the net proceeds from the offering of the Convertible Notes to repay its obligations under its 2017 Term Loan with OrbiMed. The payment amount was $79.2 million, which included the principal amount of $75.0 million, $3.8 million of early payment penalties, and $0.4 million in accrued interest. In accordance with ASC Topic 470, the Company accounted for this transaction as debt extinguishment. The difference between the reacquisition price of the debt and the net carrying amount of the debt on the extinguishment date is recorded in loss on debt extinguishment in our consolidated statements of operations and comprehensive loss. The loss on debt extinguishment was computed as follows: ​ ​ ​ ​ ​ ​ December 31, ​ ​ 2020 ​ ​ (in thousands) Debt principal balance ​ $ 75,000 Plus: early payment penalties ​ ​ 3,757 Reacquisition price of debt ​ $ 78,757 ​ ​ ​ ​ Debt principal balance ​ $ 75,000 Less: unamortized debt discount ​ ​ (2,091) Net carrying amount at extinguishment date ​ $ 72,909 ​ ​ ​ ​ Loss on debt extinguishment ​ $ 5,848 ​ Convertible Notes ​ In April 2020, the Company issued $287.5 million aggregate principal amount of Convertible Notes due 2027 in a private placement offering to qualified institutional buyers pursuant to Rule 144A under the Securities Act of 1933, as amended. ​ The Convertible Notes are senior, unsecured obligations of the Company and bear interest at a rate of 2.25% per year, payable in cash semi-annually in arrears in May and November of each year, beginning in November 2020. The Convertible Notes mature in May 2027, unless earlier converted, repurchased or redeemed in accordance with their terms. Upon conversion, the Convertible Notes are convertible into cash, shares of the Company’s common stock or a combination of cash and shares of the Company’s common stock, at the Company’s election. ​ The Company received net proceeds from the Convertible Notes of $278.3 million, after deducting the initial purchasers’ discounts and debt issuance costs. The Company used approximately $79.2 million of the net proceeds from the Convertible Notes offering to repay its obligations under the 2017 Term Loan with OrbiMed. ​ The holders of the Convertible Notes may convert all or a portion of their Convertible Notes at their option at any time prior to the close of business on the business day immediately preceding February 1, 2027 in multiples of $1,000 principal amount, under any the following circumstances: ​ ● During any fiscal quarter commencing after December 31, 2020 (and only during such fiscal quarter), if the last reported sale price of our common stock for at least 20 trading days (whether or not consecutive) during the period of 30 consecutive trading days ending on, and including, the last trading day of the immediately preceding fiscal quarter is greater than or equal to 130% of the conversion price on each applicable trading day. ​ ● During the five business day period after any five consecutive trading day period in which the trading price per $1,000 principal amount of Convertible Notes for each trading day of that five-day consecutive trading period was less than 98% of the product of the last reported sale price of the Company’s common stock and the conversion rate on each such trading day. ​ ● If the Company calls any or all of the Convertible Notes for redemption at any time prior to the close of business on the second business day prior to the redemption date. ​ ● Upon the occurrence of certain distributions. ​ ● Upon the occurrence of specified corporate transactions. ​ The Convertible Notes are convertible into shares of the Company’s common stock, par value $0.0001 per share, at an initial conversion rate of 25.7785 shares of common stock per $1,000 principal amount of the Convertible Notes, which is equivalent to an initial conversion price of approximately $38.79 per share of common stock, convertible to 7,411,704 shares of common stock. The conversion rate and corresponding conversion price are subject to adjustment upon the occurrence of certain events but will not be adjusted for any accrued or unpaid interest. The holders of the Convertible Notes who redeem their Convertible Notes in connection with a make-whole fundamental change are, under certain circumstances, entitled to an increase in the conversion rate. Additionally, in the event of a fundamental change, the holders of the Convertible Notes may require the Company to repurchase for cash all or a portion of their Convertible Notes at a price equal to 100% of the principal amount, plus any accrued and unpaid interest. ​ The Company may not redeem the Convertible Notes prior to May 2024, and no sinking fund is provided for the Convertible Notes. The Company may redeem for cash all or any portion of the Convertible Notes, at the Company’s option, on or after May 2024, if the last reported sale price of the Company’s common stock has been at least 130% of the conversion price then in effect for at least 20 trading days during any 30 consecutive trading day period ending on the trading day immediately preceding the date on which the Company provides notice of redemption. The redemption price will be equal to 100% of the principal amount of the Convertible Notes to be redeemed plus accrued and unpaid interest. The Convertible Notes are accounted for in accordance with ASC 470-20, Debt with Conversion and Other Options, as the Convertible Notes may be settled entirely or partially in cash upon conversion. The Company separately accounted for the liability component and equity component of the Convertible Notes by allocating the debt proceeds between the liability and equity components. The carrying amount of the liability component is calculated by measuring the fair value of a similar liability that does not have an associated convertible feature. The Company used a discounted cash flow method and applied the average annual market yield of 7.832% as an input to measure its fair value. The allocation was performed in a manner that reflected the Company’s non-convertible debt borrowing rate for similar debt. The carrying amount of the equity component is determined by deducting the fair value of the liability component from the initial debt proceeds. The fair value of liability component of the Convertible Notes on the date of issuance was $201.9 million, and accordingly, the remaining proceeds of $85.6 million are allocated to the equity component on the date of issuance. The carrying value of the liability component of the Convertible Notes is classified as long-term debt, and the equity component is classified as permanent equity in the Company’s consolidated balance sheet as of December 31, 2020. ​ After allocating the proceeds of the debt and equity components, the Company further allocated $9.2 million initial purchasers’ debt discount and debt issuance cost of $8.6 million and $0.6 million, respectively. The debt issuance costs primarily consisted of legal, accounting, and other professional fees. These costs were allocated to the liability and equity components based on the allocation of the proceeds as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (in thousands) ​ ​ Amount ​ ​ Equity Component ​ ​ Debt Component Debt Discount $ 8,625 ​ $ 2,568 ​ $ 6,057 Debt Issuance Cost ​ 558 ​ ​ 166 ​ ​ 392 Total $ 9,183 ​ $ 2,734 ​ $ 6,449 ​ The portion allocated to the liability component is amortized to interest expense using the effective interest method over the expected life of the Convertible Notes or approximately its seven-year term. The effective interest rate on the liability component of the Convertible Notes for the period from the date of issuance through May 2027 is 8.27%, which remains unchanged from the date of issuance. ​ The outstanding Convertible Notes balances as of December 31, 2020, are summarized in the following table: ​ ​ ​ ​ ​ ​ December 31, ​ ​ 2020 ​ ​ (in thousands) ​ Liability Component ​ ​ ​ Outstanding Principal $ 287,500 ​ Unamortized debt discount and debt issuance cost ​ (85,007) ​ Net carrying amount $ 202,493 ​ ​ At the original issuance date, the estimated fair value of the liability component of our Convertible Notes was $201.9 million and the estimated fair value of the equity component was $85.6 million as measured on the date of issuance, resulting in a total fair value of $287.5 million for the Convertible Note. The Convertible Notes were priced at par at the valuation date resulting in the fair value of the Convertible Notes equal to the principal amount of $287.5 million. The fair value of the Convertible Note has been calculated as the residual amount between the fair value of the Convertible Note and the fair value of the debt component. ​ The unamortized debt discount and issuance cost is comprised of $79.1 million of debt discount resulting from allocating proceeds to the equity component, $5.6 million of debt discount from the liability component representing the difference between the net proceeds received upon issuance of debt and the amount repayable at its maturity, and $0.4 million of debt issuance costs. ​ The following table presents total interest expense recognized related to the Convertible Notes during the year ended December 31, 2020: ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ 2020 ​ (in thousands) Cash interest expense ​ ​ ​ Contractual interest expense $ 4,582 ​ Non-cash interest expense ​ ​ ​ Amortization of debt discount and debt issuance cost ​ 7,048 ​ Total interest expense $ 11,630 ​ ​

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2020
Stockholders' Equity
Stockholders' Equity	11. Stockholders’ Equity ​ In August 2017, the Company paid OrbiMed a fee in consideration of providing the 2017 Term Loan (as defined in Note 9) by issuing 300,000 shares of its common stock. The fair value of the fee was $2.4 million, which was determined based on the Company’s stock price of $8.16 on August 8, 2017. In June 2018, OrbiMed exercised all of its warrants, which were all converted into common stock. The exercise was a cashless transaction, and there were 332,896 of net shares issued to OrbiMed following the exercise at the fair value of $6.8 million. ​ In July 2018, the Company completed an equity offering to sell 4,500,000 shares of its common stock to the public at a price of $20 per share, along with the sale of 675,000 additional shares of its common stock to the underwriters upon their exercise of the option to purchase those shares. Upon the closing of the equity offering, the Company received proceeds of $97.3 million before offering expenses, which totaled approximately $0.5 million. ​ In April 2019, the Company completed an underwritten equity offering to sell 5,263,158 shares of its common stock at a price to the public of $19 per share. On April 26, 2019, the Company sold an additional 789,473 shares of its common stock to the underwriters at the same price upon their exercise of the option to purchase those shares. Before offering expenses of $0.6 million, the Company received proceeds of $108.1 million net of the underwriting discount. In October 2019, the Company completed an underwritten equity offering to sell 5,714,286 shares of its common stock at a price to the public of $35 per share. The same day, the Company sold an additional 857,142 shares of its common stock to the underwriters at the same price upon their exercise of the option to purchase those shares. Before offering expenses of $0.4 million, the Company received proceeds of $216.2 million net of the underwriting discount. In September 2020, the Company completed an underwritten equity offering and sold 4,791,665 shares of its common stock at a price of $60.00 per share to the public. Before offering expenses of $0.3 million, the Company received proceeds of $271.0 million net of the underwriting discount. As of December 31, 2020, the Company had 50,000,000 authorized shares of its preferred stock, of which no shares were issued and outstanding issued

Disposal of Business

Disposal of Business	12 Months Ended
	Dec. 31, 2020
Disposal of Business
Disposal of Business	​ 12. Disposal of Business ​ Sale of Evercord ​ In September 2019, the Company sold the Evercord business that provides cord blood and cord tissue processing and storage services for total estimated consideration of $15.4 million, including $9.7 million in cash, $1.0 million of cash deposited in a third-party escrow account recorded in short-term other receivables, and $4.7 million of additional consideration. The additional consideration is primarily related to the accounts receivable transferred to the buyer. The cash held in escrow serve as security for the indemnification obligations of the Company and eligible for release 12 months after the closing date. The assets relating to the Evercord services transferred to the buyer had a net book value of $6.2 million as of the sale date, and consisted of accounts receivables and equipment. The obligations and liabilities relating to the Evercord services transferred to the buyer consisted of deferred revenues of $5.2 million. The sale of the Evercord business did not meet criteria to be reported as a discontinued operation, because it did not represent a strategic shift with a major effect on the Company’s operations and financial results. The Company recognized a gain of $14.4 million on the sale, which was included in Loss from operations in the Consolidated Statements of Operations and Comprehensive Loss. The following table summarizes the computation of the gain realized from the disposal of business: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ ​ ​ 2019 ​ ​ ​ ​ ​ (in thousands) ​ ​ ​ ​ ​ ​ ​ Proceeds on disposal: ​ ​ ​ ​ $ 15,377 Assets sold: ​ ​ ​ ​ ​ ​ Accounts receivable, net ​ ​ ​ ​ ​ 5,782 Equipment and inventory ​ ​ ​ ​ ​ 419 Total assets sold ​ ​ ​ ​ $ 6,201 Liabilities assumed by purchaser: ​ ​ ​ ​ ​ ​ Deferred revenues ​ ​ ​ ​ ​ 5,212 Net assets and liabilities sold ​ ​ ​ ​ $ 989 Net gain realized on disposal ​ ​ ​ ​ $ 14,388 ​ In connection with the sale of the Evercord business, the Company recorded impairment expense on the retained assets previously used in this business of $1.7 million in selling, general, and administrative expenses in the consolidated statement of operations and comprehensive loss. This expense is comprised of $1.2 million from the impairment of leasehold improvements, $0.1 million from the impairment of capitalized software held for internal use, and $0.4 million of right-of-use asset from the storage facility lease. In addition, the Company expects to incur $0.4 million of exit or disposal activity—$0.1 million of involuntary employee termination benefits were incurred in the third quarter of 2019, recorded in selling, general and administrative expense in the consolidated statements of operations and comprehensive loss, and $0.3 million of early contract termination fee from biological sample processing and storage provider to be incurred in the next fiscal year.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2020
Income Taxes
Income Taxes	13. Income Taxes ​ The Company's effective tax rates for the years ended December 31, 2020, 2019, and 2018 differ from the U.S. federal statutory rate as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ ​ 2020 ​ 2019 ​ 2018 ​ ​ ​ (in thousands, except percentages) ​ U.S. federal taxes (benefit) at statutory rate ​ $ (48,226) (21.00) % ​ $ (25,794) (21.00) % ​ $ (26,800) (21.00) % State tax expense ​ ​ (10,672) ​ (4.65) % ​ ​ (6,607) ​ (5.38) % ​ ​ (4,468) ​ (3.50) % Research and development credits ​ ​ (3,964) ​ (1.73) % ​ ​ (1,645) ​ (1.34) % ​ ​ (1,164) ​ (0.91) % Stock-based compensation ​ ​ (23,791) ​ (10.36) % ​ ​ (7,544) ​ (6.14) % ​ ​ (3,148) ​ (2.47) % Change in federal tax rate ​ ​ — ​ 0.00 % ​ ​ — ​ 0.00 % ​ ​ — ​ 0.00 % Mark to market fair value adjustments ​ ​ — ​ 0.00 % ​ ​ — ​ 0.00 % ​ ​ 865 ​ 0.68 % Nondeductible settlement for claims ​ ​ — ​ 0.00 % ​ ​ — ​ 0.00 % ​ ​ 1 ​ 0.00 % Foreign tax ​ ​ 55 ​ 0.02 % ​ ​ 1,612 ​ 1.31 % ​ ​ 195 ​ 0.15 % Other nondeductible items ​ ​ 9,776 ​ 4.26 % ​ ​ 1,378 ​ 1.12 % ​ ​ 690 ​ 0.54 % Change in valuation allowance ​ ​ 76,920 ​ 33.50 % ​ ​ 40,599 ​ 33.06 % ​ ​ 34,150 ​ 26.76 % Provision for income taxes ​ $ 98 ​ 0.04 % ​ $ 1,999 ​ 1.63 % ​ $ 321 ​ 0.25 % ​ During the year ended December 31, 2020, the Company recorded total income tax expense of $0.1 million. The Company provides testing to clinics and also licenses its cloud-based software to licensees that are based in a foreign country, which contributed to a foreign income tax expense of $0.1 million. Total income tax expense also included a state income tax benefit of $9,000 for the year ended December 31, 2020. ​ During the year ended December 31, 2019, the Company recorded total income tax expense of $2.0 million, which included a foreign withholding tax expense of $1.9 million, foreign income tax expense of $0.1 million and state income tax benefit of $0.04 million. During the year ended December 31, 2018, the Company recorded total income tax expense of $0.3 million, which included foreign income tax expense of $0.2 million and state income tax expense of $0.1 million. Deferred income taxes reflect the net tax effects of temporary differences between carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes as well as net operating loss and tax credit carryforwards. The components of the net deferred income tax assets are as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ ​ ​ ​ 2020 ​ 2019 ​ ​ ​ ​ ​ ​ (in thousands) ​ Deferred tax assets: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net operating loss carryforwards ​ ​ ​ ​ $ 177,899 ​ $ 124,777 ​ Research and development tax credit carryforwards ​ ​ ​ ​ ​ 24,332 ​ ​ 18,189 ​ Reserves and accruals ​ ​ ​ ​ ​ 21,770 ​ ​ 10,002 ​ Lease Liabilities ​ ​ ​ ​ ​ 7,123 ​ ​ 7,838 ​ Deferred revenue ​ ​ ​ ​ ​ 6,386 ​ ​ 3,288 ​ Stock-based compensation ​ ​ ​ ​ ​ 10,673 ​ ​ 6,106 ​ Total deferred tax assets before valuation allowance ​ ​ ​ ​ ​ 248,183 ​ ​ 170,200 ​ Less: valuation allowance ​ ​ ​ ​ ​ (222,521) ​ ​ (163,040) ​ ​ ​ ​ ​ ​ ​ 25,662 ​ ​ 7,160 ​ Deferred tax liabilities: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Convertible debt ​ ​ ​ ​ ​ (19,143) ​ ​ ​ ​ Right-of-use lease assets ​ ​ ​ ​ ​ (6,519) ​ ​ (7,160) ​ Net deferred tax assets ​ ​ ​ ​ $ — ​ $ — ​ ​ The Company established a full valuation allowance against its net deferred tax assets in 2020 and 2019 due to the uncertainty surrounding realization of these assets. The valuation allowance increased to $222.5 million as of December 31, 2020 from $163.0 million as of December 31, 2019 due to current year losses and credits claimed. ​ As of December 31, 2020, the Company had federal and state net operating loss (“NOLs”) carryforwards of approximately $727.2 million and $412.9 million, respectively, which begin to expire in 2027 and 2028, respectively, if not utilized. Approximately $407.3 million of federal net operating loss included above can be carried forward indefinitely. ​ The Company also had federal research and development credit carryforwards of approximately $21.4 million, which begin to expire in 2027, and state research and development credit carryforwards of approximately $16.9 million, which can be carried forward indefinitely. Realization of these deferred tax assets would require $882.4 million in taxable income to fully utilize. Realization is dependent on generating sufficient taxable income prior to expiration of the loss and credit carryforwards. ​ Federal and California tax laws impose substantial restrictions on the utilization of NOLs and credit carryforwards in the event of an "ownership change" for tax purpose, as defined in Section 382 of the Internal Revenue Code. Accordingly, the Company's ability to utilize these carryforwards may be limited as the result of such ownership change. Such a limitation could result in limitation in the use of the NOLs in future years and possibly a reduction of the NOLs available. ​ A reconciliation of the beginning and ending amount of gross unrecognized tax benefits is as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ ​ 2020 2019 ​ 2018 ​ ​ (in thousands) ​ Balance at beginning of year ​ $ 8,619 ​ $ 7,362 ​ $ 5,945 ​ Additions based on tax positions related to the current year ​ ​ 2,889 ​ ​ 1,426 ​ ​ 1,416 ​ Additions (reductions) for tax positions of prior years ​ ​ (8) ​ ​ (169) ​ ​ 1 ​ Balance at end of year ​ $ 11,500 ​ $ 8,619 ​ $ 7,362 ​ ​ During the years ended December 31, 2020, 2019, and 2018, the amount of unrecognized tax benefits increased $2.9 million, $1.3 million, and $1.4 million, respectively, due to additional research and development credits generated during the year. As of December 31, 2020, 2019, and 2018, the total amount of unrecognized tax benefits was $11.5 million, $8.6 million, and $7.4 million, respectively. The reversal of the uncertain tax benefits would not affect the Company's effective tax rate to the extent that it continues to maintain a full valuation allowance against its deferred tax assets. ​ In response to the COVID-19 pandemic, the Coronavirus Aid, Relief and Economic Security Act (CARES Act) was signed into law in March 2020. The CARES Act includes modifications for net operating loss carryovers and carrybacks, limitations of business interest expense for tax, immediate refund of alternative minimum tax (AMT) credit carryovers as well as a technical correction to the Tax Cuts and Jobs Act of 2017, for qualified improvement property. As of December 31, 2020, the Company expects that these provisions will not have a material impact as the Company has no net operating losses or AMT credits that would fall under these provisions and does not expect interest expense to be deductible due to current year losses. ​ The Company is subject to U.S. federal income taxes and to income taxes in various states in the United States. Tax regulations within each jurisdiction are subject to the interpretation of the related tax laws and regulations, and require significant judgment to apply. The Company is subject to U.S. federal, state and local tax examinations by tax authorities for all prior tax years since incorporation. The Company does not anticipate significant changes to its current uncertain tax positions through December 31, 2021. ​ The Company recognizes any interest and/or penalties related to income tax matters as a component of income tax expense. As of December 31, 2020, there were no

Net Loss per Share

Net Loss per Share	12 Months Ended
	Dec. 31, 2020
Net Loss per Share
Net Loss per Share	14. Net Loss per Share ​ Basic net loss per share attributable to common stockholders is calculated by dividing the net loss attributable to common stockholders by the weighted-average number of shares of common stock outstanding for the period. ​ In periods when the Company has incurred a net loss, common stock equivalents such as outstanding common stock options, restricted stock units, unvested common shares subject to repurchase and warrants are excluded from the calculation of diluted net loss per share as they give an anti-dilutive effect. ​ The Convertible Note is convertible as of December 31, 2020. Upon conversion, the Company has the option to pay cash, issue shares of common stock, or any combination thereof for the aggregate amount due upon conversion. The value of the Convertible Notes, if-converted, exceeds its principal amount by $388.4 million as of December 31, 2020. Since the Company is in a net loss position in the periods presented, the shares which would be issued upon conversion of the Converted Notes are excluded from the net loss per share calculation as it would have an antidilutive effect. As such, the 7.4 million shares underlying the conversion option of the Convertible Notes will not have an impact on our diluted earnings per share. If converted, the Company does not intend to settle the obligation in cash. ​ The following table provides the basic and diluted net loss per share computations for the years ended December 31, 2020, 2019, and 2018: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ ​ ​ 2020 ​ 2019 ​ 2018 ​ ​ (in thousands, except per share data) Numerator: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net loss used to compute net loss per share, basic and diluted ​ $ (229,743) ​ $ (124,827) ​ $ (128,154) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Denominator: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted-average number of shares used in computing net loss per share, basic and diluted ​ 81,011 ​ 69,555 ​ 57,848 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net loss per share, basic and diluted ​ $ (2.84) ​ $ (1.79) ​ $ (2.22) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ The following table shows the potentially dilutive common stock equivalents that were excluded from the computations of diluted net loss per share as their effect would be anti-dilutive, as of December 31, 2020, 2019, and 2018: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ ​ 2020 2019 2018 ​ (in thousands) ​ Options to purchase common stock ​ 6,707 8,497 9,463 ​ Restricted stock units ​ 4,188 ​ 2,404 ​ 1,084 ​ Employee stock purchase plan ​ 37 ​ 32 ​ 42 ​ Convertible Note ​ 7,411 ​ — ​ — ​ ​ ​ 18,343 10,933 ​ 10,589 ​ ​

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2020
Summary of Significant Accounting Policies
Basis of Presentation	Basis of Presentation ​ The accompanying consolidated financial statements have been prepared in conformity with U.S. generally accepted accounting principles (“U.S. GAAP”).
Liquidity Matters	Liquidity Matters ​ The Company has incurred net losses since its inception and anticipates net losses and negative operating cash flows for the near future. For the year ended December 31, 2020, the Company had a net loss of $229.7 million and an accumulated deficit to $929.3 million. At December 31, 2020, the Company had $48.9 million in cash, cash equivalents and restricted cash, $688.6 million in marketable securities, $50.1 million of outstanding balance of the Credit Line (as defined in Note 10) including accrued interest, and $287.5 million outstanding principal balance of the its 2.25% Convertible Senior Notes (the “Convertible Notes”). The Company used a portion of the net proceeds from the offering of the Convertible Notes to repay its obligations under its 2017 Term Loan with OrbiMed (see Note 10, Debt ​ While the Company has introduced multiple products that are generating revenues, these revenues have not been sufficient to fund all operations. Accordingly, the Company has funded the portion of operating costs that exceeds revenues through a combination of equity issuances, debt issuances, and other financings. The Company continues to develop and commercialize future products and, consequently, it will need to generate additional revenues to achieve future profitability and may need to raise additional equity or debt financing. If the Company raises additional funds by issuing equity securities, its stockholders will experience dilution. Additional debt financing, if available, may involve covenants restricting its operations or its ability to incur additional debt. Any additional debt financing or additional equity that the Company raises may contain terms that are not favorable to it or its stockholders and requires significant debt service payments, which diverts resources from other activities. Additional financing may not be available at all, or in amounts or on terms acceptable to the Company. If the Company is unable to obtain additional financing, it may be required to delay the development and commercialization of its products and significantly scale back its business and operations. In April 2019, the Company completed an underwritten equity offering and sold 6,052,631 shares of its common stock at a price of $19 per share to the public. Before offering expenses of $0.6 million, the Company received proceeds of $108.1 million net of the underwriting discount. In October 2019, the Company completed another underwritten equity offering and sold 6,571,428 shares of its common stock at a price of $35 per share to the public. Before offering expenses of $0.4 million, the Company received proceeds of $216.2 million net of the underwriting discount. In September 2020, the Company completed an additional underwritten equity offering and sold 4,791,665 shares of its common stock at a price of $60.00 per share to the public. Before offering expenses of $0.3 million, the Company received proceeds of $271.0 million net of the underwriting discount. Based on the Company’s current business plan, the Company believes that its existing cash and marketable securities will be sufficient to meet its anticipated cash requirements for at least 12 months after February 25, 2021.
Principles of Consolidation	Principles of Consolidation ​ The accompanying consolidated financial statements include all the accounts of the Company and its subsidiary. The Company established a subsidiary that operates in the state of Texas to support the Company’s laboratories and operational functions. All intercompany balances and transactions have been eliminated.
Use of Estimates	Use of Estimates ​
Cash and Cash Equivalents	Cash and Cash Equivalents ​ Cash and cash equivalents consist of cash and money market deposits with financial institutions.
Restricted Cash	Restricted Cash ​ Restricted cash is currently presented as a separate line item in the Company’s balance sheet. In the statements of cash flows, it is included together with cash and cash equivalents and considered as part of the total ending cash balance. The following is the reconciliation between how restricted cash is presented in the balance sheet and the statements of cash flows for all periods presented: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ December 31, ​ 2020 2019 ​ ​ (in thousands) Cash and cash equivalents in balance sheet ​ $ 48,668 ​ $ 61,926 Restricted cash in balance sheet ​ ​ 187 ​ ​ 55 Total cash, cash equivalents and restricted cash in statements of cash flows ​ $ 48,855 ​ $ 61,981
Investments	Investments Investments consist primarily of debt securities such as U.S. Treasuries, U.S. agency and municipal bonds. Management determines the appropriate classification of securities at the time of purchase and re-evaluates such determination at each balance sheet date. The Company generally classifies its entire investment portfolio as available-for-sale. The Company views its available-for-sale portfolio as available for use in current operations. Accordingly, the Company classifies all investments as short-term, irrespective of maturity date. Available-for-sale securities are carried at fair value, with unrealized gains and losses reported in accumulated other comprehensive income (loss), which is a separate component of stockholders’ equity.
Fair Value	Fair Value ​ The Company discloses the fair value of financial instruments for financial assets and liabilities for which the value is practicable to estimate. Fair value is defined as the price that would be received upon the sale of an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date (exit price).
Risk and Uncertainties	Risk and Uncertainties ​ The Company is subject to risks and uncertainties as a result of the COVID-19 pandemic. The extent of the impact of the COVID-19 pandemic on the Company's business is highly uncertain and difficult to predict, and the full extent and duration of the impact of the COVID 19 pandemic on our business, our operations, and the global economy as a whole is not yet known. While the Company’s test volumes as well as overall average selling prices increased in the year ended December 31, 2020 compared to the year ended December 31, 2019, the Company cannot predict the potential nature, magnitude and duration of the effects of the COVID-19 pandemic on the macroeconomic environment. Financial instruments that potentially subject the Company to credit risk consist of cash, accounts receivable and investments. The Company limits its exposure to credit loss by placing its cash in financial institutions with high credit ratings. The Company's cash may consist of deposits held with banks that may at times exceed federally insured limits. The Company performs evaluations of the relative credit standing of these financial institutions and limits the amount of credit exposure with any one institution. The Company performs evaluations of financial conditions for insurance carriers, patients, clinics and laboratory partners and generally does not require collateral to support credit sales. For the years ended December 31, 2020, 2019, and 2018, there were no customers exceeding 10% of total revenues on an individual basis. As of December 31, 2020 and 2019, there were no customers with an outstanding balance exceeding 10% of net accounts receivable.
Credit Losses	Credit Losses ​ Trade accounts receivable and other receivables. ​ The following is a roll-forward of the allowances for credit losses related to trade accounts receivable and other receivables for the year ended December 31, 2020: ​ ​ ​ ​ ​ ​ December 31, ​ ​ 2020 ​ ​ ​ (in thousands) Beginning balance ​ $ 2,919 Cumulative-effect adjustment upon adoption of ASU 2016-13 ​ ​ 404 Provision for credit losses ​ ​ 1,354 Write-offs ​ ​ (457) Total ​ $ 4,220 ​ Available-for-sale debt securities. The amended guidance from ASU 2016-13 requires the measurement of expected credit losses for available-for-sale debt securities held at the reporting date over the remaining life based on historical experience, current conditions, and reasonable and supportable forecasts. The Company evaluated its investment portfolio under the new available-for-sale debt securities impairment model guidance. The vast majority of the Company’s investment portfolio are low risk, investment grade securities.
Revenue Recognition	Revenue Recognition ​ The Company adopted the new revenue recognition guidance, ASC 606, beginning January 1, 2018 on a full retrospective basis. ASC 606 mandates revenue recognition to be evaluated using the following five steps: ​ ● Identification of a contract, or contracts, with a customer; ● Identification of the performance obligations in the contract; ● Determination of the transaction price; ● Allocation of the transaction price to the performance obligations in the contract; and ● Revenue recognition when, or as, the performance obligations are satisfied ​ Revenue Recognition,
Cost of Product Revenues	Cost of Product Revenues ​ The components of our cost of product revenues are material and service costs, impairment charges associated with testing equipment, personnel costs, including stock-based compensation expense, equipment and infrastructure expenses associated with testing samples, electronic medical records, order and delivery systems, shipping charges to transport samples, costs incurred from third party test processing fees, and allocated overhead such as rent, information technology costs, equipment depreciation and utilities. Costs associated with Whole Exome Sequencing (“WES”) are also included, as well as labor costs, relating to our Signatera CLIA offering. Costs associated with performing tests are recorded when the test is accessioned. We expect cost of product revenues in absolute dollars to increase as the number of tests we perform increases. ​
Cost of Licensing and Other Revenues	Cost of Licensing and Other Revenues ​ The components of our cost of licensing and other revenues are material costs associated with test kits sold to Constellation clients, development and support services relating to our Strategic Partnership Agreements, and costs associated with specimens and Whole Exome Sequencing (“WES”), as well as labor costs, relating to our Signatera (RUO) offering. ​ We currently have 15 revenue generating licensing and service agreements with laboratories under our Constellation distribution model. We consider our cost of licensing and other revenues for the Constellation software platform to be relatively low, and therefore we expect its associated gross margin is higher. We expect our cost of licensing will increase in relation to volume growth.
Research and Development	Research and Development ​ The Company records research and development costs in the period incurred. Research and development costs consist of personnel costs, contract services, cost of materials utilized in performing tests, costs of clinical trials and allocated facilities and related overhead expenses.
Advertising Costs	Advertising Costs ​ The Company expenses advertising costs as incurred. The Company incurred advertising costs of $0.6 million, $0.2 million, and $0.2 million for the years ended December 31, 2020, 2019, and 2018, respectively.
Product Shipment Costs	Product Shipment Costs ​ The Company expenses product shipment costs in cost of product revenues in the accompanying statements of operations. Shipping and handling costs for the years ended December 31, 2020, 2019, and 2018 were $13.3 million, $13.3 million, and $12.4 million, respectively.
Income Taxes	Income Taxes ​ Income taxes are recorded in accordance with Financial Accounting Standards Board ASC Topic 740, Income Taxes
Stock-Based Compensation	Stock-Based Compensation ​ Stock-based compensation related to stock options and restricted stock units (“RSUs”) granted to the Company’s employees is measured at the grant date based on the fair value of the award. The fair value is recognized as expense over the requisite service period, which is generally the vesting period of the respective awards. No compensation cost is recognized when the requisite service has not been met and the awards are therefore forfeited. ​ For stock options with market conditions, the Company derives the requisite service period using the Monte Carlo simulation model. For stock options and RSUs that vest upon meeting performance conditions or market conditions in combination with performance conditions, the Company derives the requisite service period from the grant date to the date it is probable that the vesting conditions will be met. ​ ​ On January 1, 2019, the Company adopted ASU 2018-07, which allows the accounting for nonemployee awards to be treated the same as for employee awards. The fair value of non-employee awards is now determined based on a one-time measurement at the grant date, and it is no longer subject to periodic remeasurement. The Company continues to recognize stock-based compensation expense as services are rendered by the non-employees over the vesting period, which is accounted for on a straight-line basis. See further discussion under the Recently Adopted Accounting Pronouncements section within this footnote, as well as the election of certain accounting policy as a result of the adoption. ​ The Company uses the Black-Scholes option-pricing model and the Monte Carlo simulation model to estimate the fair value of stock options issued to employees and non-employees. The model requires the input of the Company's expected stock price volatility, the expected term of the awards, and a risk-free interest rate. Determining these assumptions requires significant judgment. See further discussion on the valuation assumptions used under Note 9.
Capitalized Software Held for Internal Use	Capitalized Software Held for Internal Use ​ The Company capitalizes salaries and related costs of employees and consultants who devote time to the development of internal-use software development projects. Capitalization begins during the application development stage, once the preliminary project stage has been completed, which includes successful validation and approval from management. If a project constitutes an enhancement to previously developed software, the Company assesses whether the enhancement is significant and creates additional functionality to the software, thus qualifying the work incurred for capitalization. Once the project is available for general release, capitalization ceases and the Company estimates the useful life of the asset and begins amortization. The Company periodically assesses whether triggering events are present to review internal-use software for impairment. Changes in estimates related to internal-use software would increase or decrease operating expenses or amortization recorded during the reporting period. ​ The Company amortizes its internal-use software over the estimated useful lives of three years. The net book value of capitalized software held for internal use was $1.7 million and $1.2 million as of December 31, 2020 and 2019, respectively. Amortized expense for amounts previously capitalized for the years ended December 31, 2020, 2019, and 2018 was $1.0 million, $1.2 million, and $1.3 million, respectively.
Accumulated Other Comprehensive Income (Loss)	Accumulated Other Comprehensive Income (Loss) Comprehensive loss and its components encompass all changes in equity other than those with stockholders, and include net loss, unrealized gains and losses on available-for-sale marketable securities. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ ​ 2020 ​ 2019 ​ ​ (in thousands) Beginning balance ​ $ 919 ​ $ (552) Net unrealized gains on available-for-sale securities, net of tax ​ ​ 3,340 ​ ​ 1,471 Ending balance ​ $ 4,259 ​ $ 919 ​ ​ ​ ​ ​ ​ ​
Property and Equipment	Property and Equipment ​ Property and equipment, including purchased and internally developed software, are stated at cost. Depreciation is calculated using the straight-line method over the estimated useful lives of the assets, which are generally three five
Impairment of Long-lived Assets	Impairment of Long-lived Assets ​ The Company evaluates its long-lived assets for indicators of possible impairment when events or changes in circumstances indicate the carrying amount of an asset may not be recoverable. The Company then compares the carrying amounts of the assets with the future net undiscounted cash flows expected to be generated by such asset. Should an impairment exist, the impairment loss would be measured based on the excess carrying value of the asset over the asset’s fair value determined using discounted estimates of future cash flows.
Inventory	Inventory ​ Inventory is valued at the lower of the standard cost, which approximates actual cost, or market. Cost is determined using the first-in, first-out ("FIFO") method. Inventory consists entirely of supplies, which are consumed when providing its test reports, and therefore does not maintain any finished goods inventory. The Company enters into inventory purchases and commitments so that it can meet future delivery schedules based on forecasted demand for its tests. ​ The Company recorded inventory obsolescence charges totaling $0.2 million, $0.3 million, and $0.3 million in the years ended December 31, 2020, 2019, and 2018, respectively. ​
Recent Accounting Pronouncements	Recent Accounting Pronouncements ​ From time to time, new accounting pronouncements are issued by the Financial Accounting Standards Board (the “FASB”) under its accounting standard codifications (“ASC”) or other standard setting bodies and adopted by the Company as of the specified effective date. Unless otherwise discussed below, the Company believes that the impact of recently issued standards that are not yet effective will not have a material impact on its financial position or results of operations upon adoption. ​ Recently Adopted Accounting Pronouncements ​ Fair Value Measurement In August 2018, the FASB issued ASU 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement Goodwill - Internal-Use Software In August 2018, the FASB issued ASU 2018-15, Intangibles-Goodwill and Other-Internal-Use Software (Subtopic 350-40): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract Credit Losses In June 2016, the FASB issued ASU 2016-13, Financial Instruments—Credit Losses: Measurement of Credit Losses on Financial Instruments 2019-04, and ASU 2019-05. The standard requires measurement and recognition of expected credit losses for financial assets by requiring an allowance to be recorded as an offset to the amortized cost of such assets. For available-for-sale debt securities, expected credit losses should be estimated when the fair value of the debt securities is below their associated amortized costs. The Company adopted ASU 2016-13, as amended, effective January 1, 2020 using the modified retrospective method and recorded a cumulative-effect adjustment of $0.4 million in accumulated deficit as of January 1, 2020. Collaborative Arrangements In November 2018, the FASB issued ASU 2018-18, Collaborative Arrangements (Topic 808): Clarifying the Interaction between Topic 808 and Topic 606 Income Taxes In December 2019, the FASB issued ASU 2019-12, Simplifying the Accounting for Income Taxes (Topic 740), which simplifies the accounting for income taxes, eliminates certain exceptions within ASC 740, Income Taxes, and clarifies certain aspects of the current guidance to promote consistency among reporting entities. ASU 2019-12 is effective for fiscal years beginning after December 15, 2020. An entity that elects early adoption must adopt all the amendments in the same period. Most amendments within this ASU are required to be applied on a prospective basis, while certain amendments must be applied on a retrospective or modified retrospective basis. The Company has adopted this standard as of September 30, 2020, which did not have a material impact on its consolidated financial statements upon the adoption. New Accounting Pronouncements Not Yet Adopted ​ In March 2020, ASU 2020-04, Reference Rate Reform (Topic 848) In August 2020, ASU 2020-06, Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging—Contracts in Entity’s Own Equity (Subtopic 815-40) In October 2020, ASU 2020-10, Codification Improvements comprehensive income. ASU 2010-10 is effective for fiscal years beginning after December 15, 2020, including interim periods within those fiscal years. Early application of the amendments is permitted for public business entities for any annual or interim period for which financial statements have not been issued. The Company is currently evaluating the impact of the adoption of this standard on its consolidated financial statements.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2020
Summary of Significant Accounting Policies
Schedule of reconciliation of restricted cash	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ December 31, ​ 2020 2019 ​ ​ (in thousands) Cash and cash equivalents in balance sheet ​ $ 48,668 ​ $ 61,926 Restricted cash in balance sheet ​ ​ 187 ​ ​ 55 Total cash, cash equivalents and restricted cash in statements of cash flows ​ $ 48,855 ​ $ 61,981
Schedule of allowances for credit losses related to trade accounts receivable and other receivables	​ ​ ​ ​ ​ ​ December 31, ​ ​ 2020 ​ ​ ​ (in thousands) Beginning balance ​ $ 2,919 Cumulative-effect adjustment upon adoption of ASU 2016-13 ​ ​ 404 Provision for credit losses ​ ​ 1,354 Write-offs ​ ​ (457) Total ​ $ 4,220
Schedule of Accumulated Other Comprehensive Income (Loss)	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ ​ 2020 ​ 2019 ​ ​ (in thousands) Beginning balance ​ $ 919 ​ $ (552) Net unrealized gains on available-for-sale securities, net of tax ​ ​ 3,340 ​ ​ 1,471 Ending balance ​ $ 4,259 ​ $ 919 ​ ​ ​ ​ ​ ​ ​

Revenue Recognition (Tables)

Revenue Recognition (Tables)	12 Months Ended
	Dec. 31, 2020
Revenue Recognition
Schedule of disaggregation of revenues by payer types	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, ​ ​ 2020 ​ 2019 ​ 2018 ​ ​ (in thousands) Insurance carriers ​ $ 300,220 ​ $ 210,919 ​ $ 193,895 Laboratory partners ​ ​ 58,196 ​ ​ 59,876 ​ ​ 44,062 Patients ​ ​ 32,589 ​ ​ 31,533 ​ ​ 19,697 Total revenues ​ $ 391,005 ​ $ 302,328 ​ $ 257,654
Schedule of total revenue by geographic area	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year ended December 31, ​ ​ 2020 2019 2018 ​ ​ (in thousands) United States ​ $ 365,660 $ 260,846 $ 225,931 Americas, excluding U.S. ​ ​ 3,469 ​ 3,218 ​ 3,472 Europe, Middle East, India, Africa ​ ​ 14,332 ​ 15,434 ​ 20,866 Asia Pacific and Other ​ ​ 7,544 ​ 22,830 ​ 7,385 Total ​ $ 391,005 $ 302,328 ​ $ 257,654
Schedule of beginning and ending balances of accounts receivable and deferred revenues	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Balance at ​ Balance at ​ ​ December 31, ​ December 31, ​ ​ 2020 ​ 2019 ​ ​ (in thousands) Assets: ​ ​ ​ ​ ​ ​ Accounts receivable ​ $ 78,565 ​ $ 53,351 Liabilities: ​ ​ ​ ​ ​ ​ Deferred revenue, current portion ​ $ 50,125 ​ $ 56,016 Deferred revenue, long-term portion ​ ​ 22,805 ​ ​ 23,808 Total deferred revenues ​ $ 72,930 ​ $ 79,824
Schedule of changes in the balance of deferred revenues	​ ​ ​ ​ ​ ​ ​ Deferred ​ ​ Revenues ​ ​ (in thousands) Balance at December 31, 2019 ​ $ 79,824 Increase in deferred revenues ​ ​ 2,397 Reclasses from deferred revenues to other to short-term liabilities ​ ​ (799) Revenue recognized during the period that was included in ​ ​ (7,246) Revenue recognized from performance obligations satisfied ​ ​ (1,246) Balance at December 31, 2020 ​ $ 72,930
Schedule of insurance carrier reserve balance	​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, December 31, ​ 2020 2019 ​ ​ (in thousands) Beginning balance ​ $ 9,410 ​ $ 10,012 Additional reserves ​ ​ 19,427 ​ ​ 9,560 Refunds to carriers ​ ​ (6,066) ​ ​ (7,752) Reserves released to revenue ​ ​ (5,405) ​ ​ (2,410) Ending balance ​ $ 17,366 ​ $ 9,410

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2020
Fair Value Measurements
Summary of financial assets and liabilities measured on recurring basis	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2020 ​ December 31, 2019 ​ Level I Level II Level III Total Level I Level II Level III Total ​ ​ (in thousands) Financial Assets: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Money market deposits ​ $ 28,990 ​ ​ — ​ $ — ​ $ 28,990 ​ $ 22,477 ​ $ — ​ $ — ​ $ 22,477 ​ U.S. Treasury securities ​ ​ 597,744 ​ ​ — ​ ​ — ​ ​ 597,744 ​ ​ 293,157 ​ ​ — ​ ​ — ​ ​ 293,157 ​ Corporate bonds and notes ​ ​ — ​ ​ 12,328 ​ ​ — ​ ​ 12,328 ​ ​ — ​ ​ — ​ ​ — ​ ​ — ​ Municipal securities ​ ​ — ​ ​ 78,534 ​ ​ — ​ ​ 78,534 ​ ​ — ​ ​ 85,908 ​ ​ — ​ ​ 85,908 ​ Total financial assets ​ $ 626,734 ​ $ 90,862 ​ $ — ​ $ 717,596 ​ $ 315,634 ​ $ 85,908 ​ $ — ​ $ 401,542 ​

Financial Instruments (Tables)

Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2020
Financial Instruments
Schedule of available-for-sale securities	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2020 ​ December 31, 2019 ​ Amortized Gross Gross Estimated Fair Amortized Gross Gross Estimated Fair ​ ​ (in thousands) Money market deposits ​ $ 28,990 ​ $ — ​ $ — ​ $ 28,990 ​ $ 22,477 ​ $ — ​ $ — ​ $ 22,477 ​ U.S. Treasury securities (1) ​ 594,252 ​ 3,512 ​ (20) ​ 597,744 ​ 292,506 ​ 731 ​ (80) ​ 293,157 ​ Corporate bonds and notes (1) ​ 12,331 ​ 2 ​ (5) ​ 12,328 ​ — ​ — ​ — ​ — ​ Municipal securities ​ ​ 77,764 ​ ​ 796 ​ ​ (26) ​ ​ 78,534 ​ ​ 85,638 ​ ​ 277 ​ ​ (7) ​ ​ 85,908 ​ Total ​ $ 713,337 ​ $ 4,310 ​ $ (51) ​ $ 717,596 ​ $ 400,621 ​ $ 1,008 ​ $ (87) ​ $ 401,542 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Classified as: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Cash equivalents (2) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ $ 28,990 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ $ 22,477 ​ Short-term investments ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 688,606 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 379,065 ​ Total ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ $ 717,596 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ $ 401,542 ​
Summarized portfolio of available-for-sale securities by contractual maturity	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2020 ​ ​ ​ Amortized ​ Fair ​ ​ ​ (in thousands) ​ Less than or equal to one year ​ $ 322,416 ​ $ 323,002 ​ Greater than one year but less than five years ​ ​ 361,931 ​ ​ 365,604 ​ Total ​ $ 684,347 ​ $ 688,606 ​

Balance Sheet Components (Table

Balance Sheet Components (Tables)	12 Months Ended
	Dec. 31, 2020
Balance Sheet Components
Schedule of allowance for doubtful accounts	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ December 31, ​ December 31, ​ 2020 ​ 2019 ​ 2018 ​ (in thousands) Beginning balance $ 2,919 ​ $ 1,788 ​ $ 2,000 Cumulative-effect adjustment upon adoption of ASU 2016-13 ​ 404 ​ ​ — ​ ​ — Provision for credit losses ​ 1,354 ​ ​ 1,141 ​ ​ (41) Write offs ​ (457) ​ ​ (10) ​ ​ (171) Ending balance $ 4,220 ​ $ 2,919 ​ $ 1,788 ​ ​ ​ ​ ​ ​ ​ ​ ​
Schedule of property and equipment	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ December 31, ​ ​ Useful Life 2020 2019 ​ ​ ​ ​ ​ (in thousands) ​ Machinery and equipment 3-5 years $ 51,001 ​ $ 36,414 ​ Furniture and fixtures 3 years ​ 1,376 ​ 1,376 ​ Computer equipment 3 years ​ 2,428 ​ 1,828 ​ Capitalized software held for internal use ​ 3 years ​ ​ 7,417 ​ ​ 5,917 ​ Leasehold improvements Life of lease ​ 14,810 ​ 11,556 ​ Construction-in-process ​ ​ ​ 6,370 ​ 7,716 ​ ​ ​ ​ ​ 83,402 ​ 64,807 ​ Less: Accumulated depreciation and amortization ​ ​ ​ (50,054) ​ (41,524) ​ Total Property and Equipment, net ​ ​ ​ $ 33,348 ​ $ 23,283 ​
Schedule of accrued compensation	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, December 31, ​ ​ 2020 2019 ​ ​ (in thousands) ​ Accrued paid time off ​ $ 2,260 ​ $ 1,850 ​ Accrued commissions ​ 12,686 ​ 5,767 ​ Accrued bonuses ​ 9,635 ​ 5,710 ​ Other accrued compensation ​ 5,790 ​ 2,761 ​ Total accrued compensation ​ $ 30,371 ​ $ 16,088 ​
Schedule of other accrued liabilities	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, December 31, ​ 2020 2019 ​ ​ (in thousands) Reserves for refunds to insurance carriers ​ $ 17,366 ​ $ 9,410 ​ Accrued charges for third-party testing ​ ​ 5,141 ​ ​ 8,408 ​ Testing and laboratory materials from suppliers ​ ​ 2,720 ​ ​ 4,301 ​ Marketing and corporate affairs ​ ​ 3,325 ​ ​ 2,957 ​ Legal, audit and consulting fees ​ ​ 4,189 ​ ​ 2,873 ​ Accrued shipping charges ​ ​ 1,604 ​ ​ 305 ​ Sales tax payable ​ ​ 1,723 ​ ​ 1,691 ​ Accrued specimen service fees ​ ​ 2,355 ​ ​ 2,269 ​ Clinical trials and studies ​ 2,353 ​ 1,092 ​ Operating lease liabilities, current portion ​ ​ 7,300 ​ ​ 5,739 ​ Fixed asset purchases ​ ​ 1,691 ​ ​ 1,482 ​ Other accrued interest ​ ​ 1,078 ​ ​ — ​ Other accrued expenses ​ 9,562 ​ 8,516 ​ Total other accrued liabilities ​ $ 60,407 ​ $ 49,043 ​

Leases (Tables)

Leases (Tables)	12 Months Ended
	Dec. 31, 2020
Leases
Schedule of lease liabilities	​ ​ ​ ​ ​ ​ ​ December 31, ​ ​ 2020 ​ ​ (in thousands) Operating lease liabilities, current portion included in other accrued liabilities ​ $ 7,300 Operating lease liabilities, long-term portion ​ ​ 21,246 Total operating lease liabilities ​ $ 28,546
Schedule of annual minimum lease payments	​ ​ ​ ​ ​ ​ ​ Operating Leases ​ ​ (in thousands) Year ending December 31: ​ ​ ​ ​ 2021 ​ $ 9,958 ​ 2022 ​ ​ 10,242 ​ 2023 ​ ​ 8,670 ​ 2024 ​ ​ 2,400 ​ 2025 ​ ​ 2,447 ​ 2026 and thereafter ​ ​ 2,283 ​ Total future minimum lease payments ​ ​ 36,000 ​ Less: imputed interest ​ ​ (7,454) ​ Operating lease liabilities ​ $ 28,546 ​

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2020
Commitments and Contingencies
Schedule of material contractual commitments	​ ​ ​ ​ ​ Party Total Commitments Expiry Date ​ ​ (in thousands) ​ Laboratory instruments supplier $ 3,490 December 2021 Material suppliers ​ 17,280 June 2026 Application service providers ​ 39,425 January 2024 Gene sequencing reagents and kits provider ​ 135 April 2021 Software development provider ​ 4,000 December 2024 Other material suppliers ​ 11,690 Various ​ ​ 76,020 ​ ​ ​ ​ ​

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Summary of offering activity	​ ​ ​ ​ ​ ​ ​ ​ ​ Number of ​ Total ​ ​ Shares Purchased ​ Proceeds Offering Period ​ (in thousands) November 1, 2018 - April 30, 2019 ​ 132,177 ​ $ 2,147 May 1, 2019 - October 31, 2019 ​ 136,084 ​ ​ 2,176 November 1, 2019 - April 30, 2020 ​ 97,247 ​ ​ 3,061 May 1, 2020 - October 31, 2020 ​ 136,288 ​ ​ 4,052
Summary of stock option activity	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Outstanding Options ​ ​ ​ ​ Weighted- ​ ​ ​ ​ ​ ​ ​ Weighted- ​ Average ​ ​ ​ ​ Shares ​ ​ ​ Average ​ Remaining ​ Aggregate ​ ​ Available for ​ Number of ​ Exercise ​ Contractual ​ Intrinsic ​ ​ Grant ​ Shares ​ Price ​ Life ​ Value (in thousands, except for contractual life and exercise price) ​ ​ ​ ​ ​ ​ ​ ​ (in years) ​ ​ Balance at December 31, 2019 6,416 8,497 ​ $ 10.39 6.88 ​ $ 197,955 ​ Additional shares authorized 3,120 ​ — ​ $ — ​ ​ ​ ​ ​ ​ Options granted (457) 457 ​ $ 27.67 ​ ​ ​ ​ ​ ​ Options exercised — (2,092) ​ $ 11.24 ​ ​ ​ ​ ​ ​ Options forfeited/cancelled 155 (155) ​ $ 15.39 ​ ​ ​ ​ ​ ​ RSUs granted ​ (6,204) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ RSUs forfeited/cancelled ​ 436 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Balance at December 31, 2020 3,466 6,707 ​ $ 11.19 6.04 ​ $ 592,468 ​ Exercisable at December 31, 2020 ​ ​ 5,080 ​ $ 9.04 5.40 ​ $ 459,683 ​ Vested and expected to vest at December 31, 2020 ​ ​ 6,609 ​ $ 11.09 6.01 ​ $ 584,396 ​
Schedule of performance-based awards	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Period Granted ​ Options Granted ​ RSUs Granted ​ Options Vested ​ RSUs Vested ​ Milestone ​ Valuation Method (in thousands) Q1 2019 ​ 200 ​ 300 ​ 138 ​ 219 ​ (1) ​ Monte-Carlo Simulation Q2 2019 ​ — ​ 188 ​ — ​ — ​ (2) ​ Fair Market Value Q3 2019 ​ — ​ 50 ​ — ​ 25 ​ (1) ​ Monte-Carlo Simulation Q1 2020 ​ 150 ​ 300 ​ 75 ​ 150 ​ (1) ​ Monte-Carlo Simulation Q1 2020 ​ — ​ 436 ​ — ​ 4 ​ (3) ​ Fair Market Value Q1 2020 ​ 129 ​ — ​ — ​ — ​ (3) ​ Black-Scholes-Merton Q2 2020 ​ — ​ 21 ​ — ​ — ​ (3) ​ Fair Market Value Q3 2020 ​ 10 ​ — ​ 10 ​ — ​ (4) ​ Black-Scholes-Merton Q3 2020 ​ — ​ 27 ​ — ​ 5 ​ (3) ​ Fair Market Value Q4 2020 ​ — ​ 32 ​ — ​ — ​ (1) ​ Monte-Carlo Simulation Q4 2020 ​ — ​ 22 ​ — ​ — ​ (5) ​ Fair Market Value ​ (1) The awards vest based on the achievement of certain values of the Company’s common stock at multiple thresholds within certain periods and are contingent upon the completion of requisite service through the date of such vesting. (2) The vesting of the awards will be triggered after the end of the achievement milestone, as measured by the Company. (3) The awards vest based on achievement of certain revenue targets and are contingent upon the completion of requisite service through the date of such vesting. (4) The awards vest based on achievement of a reimbursement target. (5) The awards will vest based on achievement of certain revenue and recruiting targets.
Restricted stock units	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted- ​ ​ ​ ​ Average ​ ​ Number of ​ Grant Date ​ ​ Shares ​ Fair Value ​ ​ (in thousands) ​ ​ ​ Balance at December 31, 2019 ​ 2,404 ​ $ 19.86 Granted ​ 3,102 ​ $ 39.94 Vested ​ (1,100) ​ $ 19.69 Canceled/Forfeited ​ (218) ​ $ 24.70 Balance at December 31, 2020 4,188 ​ $ 34.02 ​ ​ ​ ​ ​ ​
Summary of stock-based compensation expenses	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year ended December 31, ​ ​ 2020 ​ 2019 ​ 2018 ​ Employee Non-Employee Total Employee Non-Employee Total Employee Non-Employee Total ​ (in thousands) ​ Cost of revenues ​ $ 1,691 ​ $ — ​ $ 1,691 ​ $ 905 ​ $ 32 ​ $ 937 ​ $ 564 ​ $ 5 ​ $ 569 ​ Research and development ​ 10,777 ​ 647 ​ 11,424 ​ 5,354 ​ — ​ 5,354 ​ ​ 4,043 ​ — ​ 4,043 ​ Selling, general and administrative ​ 36,747 ​ 309 ​ 37,056 ​ 21,730 ​ 603 ​ 22,333 ​ ​ 9,474 ​ 112 ​ 9,586 ​ Total ​ $ 49,215 ​ $ 956 ​ $ 50,171 ​ $ 27,989 ​ $ 635 ​ $ 28,624 ​ $ 14,081 ​ $ 117 ​ $ 14,198 ​
Performance-based awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Schedule of assumptions used in valuation of fair value	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, December 31, ​ 2020 2019 Risk-free interest rate ​ 0.54 % — 1.64 % ​ 1.63 % — 2.61 % Expected dividend yield ​ ​ ​ ​ — ​ ​ ​ ​ ​ — ​ Expected volatility ​ 55 % — 65 % ​ ​ ​ ​ 50 % Expected term (years) ​ 5.25 ​ — 7.25 ​ ​ ​ ​ ​ 7.25 ​
Employee stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Schedule of assumptions used in valuation of fair value	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year ended December 31, ​ 2020 2019 2018 ​ Expected term (years) 5.22 ​ — 10.00 ​ ​ 5.23 ​ — 10.00 ​ ​ 5.24 ​ — 5.62 ​ Expected volatility 49.94 % — 61.96 % 42.53 % — 45.84 % ​ 40.28 % — 42.53 % Expected dividend rate ​ ​ ​ 0 % ​ ​ ​ 0 % ​ ​ ​ ​ 0 % Risk-free interest rate 0.31 % — 1.70 % 1.60 % — 2.60 % ​ 2.37 % — 3.06 %

Debt (Tables)

Debt (Tables)	12 Months Ended
	Dec. 31, 2020
Debt
Schedule of debt extinguishment	​ ​ ​ ​ ​ ​ December 31, ​ ​ 2020 ​ ​ (in thousands) Debt principal balance ​ $ 75,000 Plus: early payment penalties ​ ​ 3,757 Reacquisition price of debt ​ $ 78,757 ​ ​ ​ ​ Debt principal balance ​ $ 75,000 Less: unamortized debt discount ​ ​ (2,091) Net carrying amount at extinguishment date ​ $ 72,909 ​ ​ ​ ​ Loss on debt extinguishment ​ $ 5,848
Summary of costs of liability and equity components	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (in thousands) ​ ​ Amount ​ ​ Equity Component ​ ​ Debt Component Debt Discount $ 8,625 ​ $ 2,568 ​ $ 6,057 Debt Issuance Cost ​ 558 ​ ​ 166 ​ ​ 392 Total $ 9,183 ​ $ 2,734 ​ $ 6,449
Schedule of outstanding Convertible Notes	​ ​ ​ ​ ​ ​ December 31, ​ ​ 2020 ​ ​ (in thousands) ​ Liability Component ​ ​ ​ Outstanding Principal $ 287,500 ​ Unamortized debt discount and debt issuance cost ​ (85,007) ​ Net carrying amount $ 202,493 ​
Summary of interest expense	​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ 2020 ​ (in thousands) Cash interest expense ​ ​ ​ Contractual interest expense $ 4,582 ​ Non-cash interest expense ​ ​ ​ Amortization of debt discount and debt issuance cost ​ 7,048 ​ Total interest expense $ 11,630 ​

Disposal of Business (Tables)

Disposal of Business (Tables)	12 Months Ended
	Dec. 31, 2020
Disposal of Business
Schedule of computation of the gain realized from the disposal of business	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ ​ ​ 2019 ​ ​ ​ ​ ​ (in thousands) ​ ​ ​ ​ ​ ​ ​ Proceeds on disposal: ​ ​ ​ ​ $ 15,377 Assets sold: ​ ​ ​ ​ ​ ​ Accounts receivable, net ​ ​ ​ ​ ​ 5,782 Equipment and inventory ​ ​ ​ ​ ​ 419 Total assets sold ​ ​ ​ ​ $ 6,201 Liabilities assumed by purchaser: ​ ​ ​ ​ ​ ​ Deferred revenues ​ ​ ​ ​ ​ 5,212 Net assets and liabilities sold ​ ​ ​ ​ $ 989 Net gain realized on disposal ​ ​ ​ ​ $ 14,388

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2020
Income Taxes
Schedule of effective tax rates differing from U.S. federal statutory rate	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ ​ 2020 ​ 2019 ​ 2018 ​ ​ ​ (in thousands, except percentages) ​ U.S. federal taxes (benefit) at statutory rate ​ $ (48,226) (21.00) % ​ $ (25,794) (21.00) % ​ $ (26,800) (21.00) % State tax expense ​ ​ (10,672) ​ (4.65) % ​ ​ (6,607) ​ (5.38) % ​ ​ (4,468) ​ (3.50) % Research and development credits ​ ​ (3,964) ​ (1.73) % ​ ​ (1,645) ​ (1.34) % ​ ​ (1,164) ​ (0.91) % Stock-based compensation ​ ​ (23,791) ​ (10.36) % ​ ​ (7,544) ​ (6.14) % ​ ​ (3,148) ​ (2.47) % Change in federal tax rate ​ ​ — ​ 0.00 % ​ ​ — ​ 0.00 % ​ ​ — ​ 0.00 % Mark to market fair value adjustments ​ ​ — ​ 0.00 % ​ ​ — ​ 0.00 % ​ ​ 865 ​ 0.68 % Nondeductible settlement for claims ​ ​ — ​ 0.00 % ​ ​ — ​ 0.00 % ​ ​ 1 ​ 0.00 % Foreign tax ​ ​ 55 ​ 0.02 % ​ ​ 1,612 ​ 1.31 % ​ ​ 195 ​ 0.15 % Other nondeductible items ​ ​ 9,776 ​ 4.26 % ​ ​ 1,378 ​ 1.12 % ​ ​ 690 ​ 0.54 % Change in valuation allowance ​ ​ 76,920 ​ 33.50 % ​ ​ 40,599 ​ 33.06 % ​ ​ 34,150 ​ 26.76 % Provision for income taxes ​ $ 98 ​ 0.04 % ​ $ 1,999 ​ 1.63 % ​ $ 321 ​ 0.25 %
Schedule of tax effects of temporary differences that give rise to significant portions of the deferred tax assets	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ ​ ​ ​ 2020 ​ 2019 ​ ​ ​ ​ ​ ​ (in thousands) ​ Deferred tax assets: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net operating loss carryforwards ​ ​ ​ ​ $ 177,899 ​ $ 124,777 ​ Research and development tax credit carryforwards ​ ​ ​ ​ ​ 24,332 ​ ​ 18,189 ​ Reserves and accruals ​ ​ ​ ​ ​ 21,770 ​ ​ 10,002 ​ Lease Liabilities ​ ​ ​ ​ ​ 7,123 ​ ​ 7,838 ​ Deferred revenue ​ ​ ​ ​ ​ 6,386 ​ ​ 3,288 ​ Stock-based compensation ​ ​ ​ ​ ​ 10,673 ​ ​ 6,106 ​ Total deferred tax assets before valuation allowance ​ ​ ​ ​ ​ 248,183 ​ ​ 170,200 ​ Less: valuation allowance ​ ​ ​ ​ ​ (222,521) ​ ​ (163,040) ​ ​ ​ ​ ​ ​ ​ 25,662 ​ ​ 7,160 ​ Deferred tax liabilities: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Convertible debt ​ ​ ​ ​ ​ (19,143) ​ ​ ​ ​ Right-of-use lease assets ​ ​ ​ ​ ​ (6,519) ​ ​ (7,160) ​ Net deferred tax assets ​ ​ ​ ​ $ — ​ $ — ​
Schedule of reconciliation of the beginning and ending amount of gross unrecognized tax benefits	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ ​ 2020 2019 ​ 2018 ​ ​ (in thousands) ​ Balance at beginning of year ​ $ 8,619 ​ $ 7,362 ​ $ 5,945 ​ Additions based on tax positions related to the current year ​ ​ 2,889 ​ ​ 1,426 ​ ​ 1,416 ​ Additions (reductions) for tax positions of prior years ​ ​ (8) ​ ​ (169) ​ ​ 1 ​ Balance at end of year ​ $ 11,500 ​ $ 8,619 ​ $ 7,362 ​

Net Loss per Share (Tables)

Net Loss per Share (Tables)	12 Months Ended
	Dec. 31, 2020
Net Loss per Share
Basic and diluted net loss per share	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ ​ ​ 2020 ​ 2019 ​ 2018 ​ ​ (in thousands, except per share data) Numerator: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net loss used to compute net loss per share, basic and diluted ​ $ (229,743) ​ $ (124,827) ​ $ (128,154) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Denominator: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted-average number of shares used in computing net loss per share, basic and diluted ​ 81,011 ​ 69,555 ​ 57,848 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net loss per share, basic and diluted ​ $ (2.84) ​ $ (1.79) ​ $ (2.22) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​
Total outstanding potentially dilutive shares not included in the calculation of dilutive EPS	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ ​ 2020 2019 2018 ​ (in thousands) ​ Options to purchase common stock ​ 6,707 8,497 9,463 ​ Restricted stock units ​ 4,188 ​ 2,404 ​ 1,084 ​ Employee stock purchase plan ​ 37 ​ 32 ​ 42 ​ Convertible Note ​ 7,411 ​ — ​ — ​ ​ ​ 18,343 10,933 ​ 10,589 ​

Description of Business (Detail

Description of Business (Details)	12 Months Ended
	Dec. 31, 2020segment
Description of Business
Number of operating segments	1

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Liquidity Matters (Details) - USD ($) $ / shares in Units, $ in Thousands	Apr. 26, 2019	Sep. 30, 2020	Apr. 30, 2020	Oct. 31, 2019	Apr. 30, 2019	Jul. 31, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Apr. 23, 2019	Dec. 31, 2017
Policies
Net (loss) income							$ (229,743)	$ (124,827)	$ (128,154)
Accumulated deficit							929,318	699,171
Cash, cash equivalents and restricted cash							48,855	61,981	$ 51,004		$ 13,021
Marketable securities							688,606	379,065
Short-term Credit Line, outstanding balance							$ 50,054	$ 50,123
Common stock, shares issued		4,791,665		5,714,286	5,263,158	4,500,000	86,223,000	78,005,000
Stock issued (in dollars per share)				$ 35	$ 19	$ 20
Payment of offering expenses	$ 600	$ 300		$ 400	$ 600	$ 500
Proceeds from issuance of common stock	$ 108,100	$ 271,000		$ 216,200	$ 108,100	$ 97,300
Net proceeds							$ 278,316
Loss on Debt Extinguishment							5,848
Convertible Notes
Policies
Outstanding principal balance			$ 287,500				287,500
Per annum interest rate (as a percent)			2.25%
Debt principal balance							287,500
2.25% Convertible Senior Notes
Policies
Outstanding principal balance							$ 287,500
Per annum interest rate (as a percent)							2.25%
Equity offering
Policies
Common stock, shares issued		4,791,665		6,571,428						6,052,631
Stock issued (in dollars per share)		$ 60		$ 35						$ 19
Option for additional shares
Policies
Common stock, shares issued	789,473			857,142		675,000

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Restricted Cash (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Summary of Significant Accounting Policies
Cash and cash equivalents in balance sheet	$ 48,668	$ 61,926
Restricted cash in balance sheet	187	55
Total cash, cash equivalents and restricted cash in statements of cash flows	$ 48,855	$ 61,981	$ 51,004	$ 13,021

Summary of Significant Accoun_6

Summary of Significant Accounting Policies - Concentration (Details) - customer	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Sales | Customer
Risk and Uncertainties
Number of customers exceeding 10% of benchmark	0	0	0
Accounts receivable | Credit
Risk and Uncertainties
Number of customers exceeding 10% of benchmark	0	0

Summary of Significant Accoun_7

Summary of Significant Accounting Policies - Credit Losses (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Summary of Significant Accounting Policies
Beginning balance	$ 2,919	$ 1,788	$ 2,000
Cumulative-effect adjustment upon adoption of ASU 2016-13	404	200
Provision for credit losses	1,354	1,141	(41)
Write-offs	(457)	(10)	(171)
Ending balance	$ 4,220	$ 2,919	$ 1,788

Summary of Significant Accoun_8

Summary of Significant Accounting Policies - Costs (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020USD ($)agreement	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)
Number of licensing and service agreements | agreement	15
Advertising costs	$ 0.6	$ 0.2	$ 0.2
Capitalized software	$ 1.7	1.2
Impairment of capitalized software		0.1
Capitalized software held for internal use
Estimated useful life (in years)	3 years
Amortized expense	$ 1	1.2	1.3
Shipping and handling costs
Cost of revenues	$ 13.3	$ 13.3	$ 12.4

Summary of Significant Accoun_9

Summary of Significant Accounting Policies - AOCIL (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	$ 919	$ (552)
Ending balance	4,259	919
Net unrealized gain (loss) on available-for-sale securities, net of tax
Accumulated Other Comprehensive Income (Loss) [Line Items]
Increase (decrease) in other comprehensive loss	$ 3,340	$ 1,471

Summary of Significant Accou_10

Summary of Significant Accounting Policies - Property (Details) - Machinery and equipment	12 Months Ended
	Dec. 31, 2020
Minimum
Property and Equipment
Estimated useful life	P3Y
Maximum
Property and Equipment
Estimated useful life	P5Y

Summary of Significant Accou_11

Summary of Significant Accounting Policies - Inventory (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Summary of Significant Accounting Policies
Inventory obsolescence charges	$ 0.2	$ 0.3	$ 0.3

Summary of Significant Accou_12

Summary of Significant Accounting Policies - Accounting Pronouncements (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect adjustment	$ 404	$ 200
ASU 2016-13
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect adjustment		$ 400

Revenue Recognition (Details)

Revenue Recognition (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended	12 Months Ended
	Feb. 28, 2019	Jun. 30, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Aug. 31, 2019
Deferred revenue, Long-term			$ 22,805	$ 23,808
Other assets			14,743	12,476
Deferred revenue			72,930	79,824
Deferred revenue, current portion			50,125	56,016
Total revenues			391,005	302,328	$ 257,654
Deferred revenue, long-term portion			22,805	23,808
Revenue recognized during the period that was included in deferred revenues at the beginning of the period			7,246
Product
Revenue recognized			5,400	2,400	3,300
Cost of revenues			185,865	162,604	158,081
Total revenues			367,211	269,881	240,366
Licensing and other
Cost of revenues			17,755	12,866	7,974
Total revenues			23,794	32,447	17,288
Genetic testing services and provision of IVD kits
Revenue recognized during the period that was included in deferred revenues at the beginning of the period			$ 400
Qiagen
Proceeds from license agreement					5,000
Agreement term			10 years
Revenue, remaining performance obligation					40,000
Qiagen | Volume, regulatory and commercial milestones
Revenue, remaining performance obligation					$ 10,000
Qiagen | Prepaid royalties
Revenue recognized			$ 0
BGI Genomics
Proceeds from license agreement	$ 50,000	$ 35,600
Receivable		2,500
Deferred revenue, current portion			3,900
BGI Genomics | Sequencing services
Other assets		6,000
BGI Genomics | Sequencing products
Other assets		4,000
BGI Genomics | Sequencing products and services
Other assets		$ 10,000	10,000
Foundation Medicine ("FMI")
Proceeds from license agreement			$ 0	16,300
Agreement term			5 years
Automatic renewals, successive period thereafter			1 year
Deferred revenue, current portion			$ 6,200
Foundation Medicine ("FMI") | Upfront licensing fees and prepaid revenues
Initial transaction price						$ 13,300
Foundation Medicine ("FMI") | Developmental, regulatory, and commercial milestones
Initial transaction price						$ 32,000
Foundation Medicine ("FMI") | Developmental performance milestones
Proceeds from license agreement				3,000
Foundation Medicine ("FMI") | Licensing fees and prepaid revenue
Proceeds from license agreement				$ 13,300

Revenue Recognition - Disaggreg

Revenue Recognition - Disaggregation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disaggregation of Revenue [Line Items]
Total revenues	$ 391,005	$ 302,328	$ 257,654
United States
Disaggregation of Revenue [Line Items]
Total revenues	365,660	260,846	225,931
Americas, excluding U.S.
Disaggregation of Revenue [Line Items]
Total revenues	3,469	3,218	3,472
Europe, Middle East, India, and Africa
Disaggregation of Revenue [Line Items]
Total revenues	14,332	15,434	20,866
Asia Pacific and Other
Disaggregation of Revenue [Line Items]
Total revenues	7,544	22,830	7,385
Insurance carriers
Disaggregation of Revenue [Line Items]
Total revenues	300,220	210,919	193,895
Laboratory partners
Disaggregation of Revenue [Line Items]
Total revenues	58,196	59,876	44,062
Patients
Disaggregation of Revenue [Line Items]
Total revenues	32,589	31,533	19,697
Product
Disaggregation of Revenue [Line Items]
Total revenues	367,211	269,881	240,366
Licensing and other
Disaggregation of Revenue [Line Items]
Total revenues	$ 23,794	$ 32,447	$ 17,288

Revenue Recognition - Accounts

Revenue Recognition - Accounts Receivable and Deferred Revenue (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Assets
Accounts receivable	$ 78,565	$ 53,351
Liabilities:
Deferred revenue, current portion	50,125	56,016
Deferred revenue, long-term portion	22,805	23,808
Total deferred revenues	72,930	79,824
Current accounts receivable	78,565	53,351
Other noncurrent assets	$ 14,743	$ 12,476

Revenue Recognition - Changes i

Revenue Recognition - Changes in Balance of Deferred Revenues (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020USD ($)
Revenue Recognition
Balance	$ 79,824
Increase in deferred revenues	2,397
Reclasses from deferred revenues to other short-term liabilities	(799)
Revenue recognized during the period that was included in deferred revenues at the beginning of the period	(7,246)
Revenue recognized from performance obligations satisfied within the same period	(1,246)
Balance	$ 72,930

Revenue Recognition - Deferred

Revenue Recognition - Deferred Revenues (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Revenue recognized during the period that was included in deferred revenues at the beginning of the period	$ 7,246
Deferred revenue, current portion	50,125	$ 56,016
Deferred revenue, Long-term	22,805	23,808
Deferred revenue	72,930	$ 79,824
BGI Genomics
Deferred revenue, current portion	3,900
Foundation Medicine ("FMI")
Deferred revenue, current portion	6,200
BGI Genomics and Foundation Medicine (including genetic testing services)
Revenue recognized during the period that was included in deferred revenues at the beginning of the period	7,200
BGI Genomics and Foundation Medicine ("FMI")
Revenue recognized during the period that was included in deferred revenues at the beginning of the period	6,800
Revenue recognized	1,200
Genetic testing services and provision of IVD kits
Revenue recognized during the period that was included in deferred revenues at the beginning of the period	$ 400

Fair Value Measurements (Detail

Fair Value Measurements (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Transfers between Levels 1 and 2
Fair value, assets transfers between Level 1 and Level II	$ 0
Recurring | Available-for-sale securities
Financial Assets:
Total financial assets	717,596	$ 401,542
Recurring | Money market deposits
Financial Assets:
Total financial assets	28,990	22,477
Recurring | U.S. Treasury securities
Financial Assets:
Total financial assets	597,744	293,157
Recurring | Corporate bonds and notes
Financial Assets:
Total financial assets	12,328
Recurring | Municipal securities
Financial Assets:
Total financial assets	78,534	85,908
Recurring | Level 1 | Available-for-sale securities
Financial Assets:
Total financial assets	626,734	315,634
Recurring | Level 1 | Money market deposits
Financial Assets:
Total financial assets	28,990	22,477
Recurring | Level 1 | U.S. Treasury securities
Financial Assets:
Total financial assets	597,744	293,157
Recurring | Level 2 | Available-for-sale securities
Financial Assets:
Total financial assets	90,862	85,908
Recurring | Level 2 | Corporate bonds and notes
Financial Assets:
Total financial assets	12,328
Recurring | Level 2 | Municipal securities
Financial Assets:
Total financial assets	$ 78,534	$ 85,908

Financial Instruments (Details)

Financial Instruments (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020USD ($)position	Dec. 31, 2019USD ($)position
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Estimated Fair Value	$ 688,606	$ 379,065
Amount of investments sold	$ 30,100	$ 0
Number of investments, unrealized loss position | position	13	13
Unrealized loss position	$ 144,000
Amortized Cost
Less than or equal to one year	322,416
Greater than one year but less than five years	361,931
Total	684,347
Fair Value
Less than or equal to one year	323,002
Greater than or equal to one year but less than five years	365,604
Total	688,606
Available-for-sale securities
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized Cost	713,337	$ 400,621
Unrealized Gain	4,310	1,008
Unrealized Loss	(51)	(87)
Estimated Fair Value	717,596	401,542
Money market deposits
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized Cost	28,990	22,477
Estimated Fair Value	28,990	22,477
U.S. Treasury securities
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized Cost	594,252	292,506
Unrealized Gain	3,512	731
Unrealized Loss	(20)	(80)
Estimated Fair Value	597,744	293,157
Corporate bonds and notes
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized Cost	12,331
Unrealized Gain	2
Unrealized Loss	(5)
Estimated Fair Value	12,328
Municipal securities
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized Cost	77,764	85,638
Unrealized Gain	796	277
Unrealized Loss	(26)	(7)
Estimated Fair Value	78,534	85,908
Cash equivalents | Available-for-sale securities
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Estimated Fair Value	28,990	22,477
Short-term investments | Available-for-sale securities
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Estimated Fair Value	$ 688,606	$ 379,065

Balance Sheet Components - Allo

Balance Sheet Components - Allowance for Doubtful Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Allowance for doubtful accounts
Beginning balance	$ 2,919	$ 1,788	$ 2,000
Cumulative-effect adjustment upon adoption of ASU 2016-13	404
Provision for credit losses	1,354	1,141	(41)
Write-offs	(457)	(10)	(171)
Ending balance	$ 4,220	$ 2,919	$ 1,788

Balance Sheet Components - Prop

Balance Sheet Components - Property and Equipment, net (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Property and Equipment, net
Property and equipment, gross	$ 83,402	$ 64,807
Less: Accumulated depreciation and amortization	(50,054)	(41,524)
Total Property and Equipment, net	33,348	23,283
Impairment		1,671	$ 1,544
Impairment of leasehold improvements		1,200
Impairment of capitalized software		100
Impairment of right-of-use assets		400
Selling, general and administrative
Property and Equipment, net
Impairment		1,700
Machinery and equipment
Property and Equipment, net
Property and equipment, gross	51,001	36,414
Furniture and fixtures
Property and Equipment, net
Property and equipment, gross	$ 1,376	1,376
Useful Life	3 years
Computer equipment
Property and Equipment, net
Property and equipment, gross	$ 2,428	1,828
Useful Life	3 years
Capitalized software held for internal use
Property and Equipment, net
Property and equipment, gross	$ 7,417	5,917
Useful Life	3 years
Leasehold improvements
Property and Equipment, net
Property and equipment, gross	$ 14,810	11,556
Construction-in-process
Property and Equipment, net
Property and equipment, gross	$ 6,370	$ 7,716
Minimum | Machinery and equipment
Property and Equipment, net
Useful Life	3 years
Maximum | Machinery and equipment
Property and Equipment, net
Useful Life	5 years

Balance Sheet Components - Othe

Balance Sheet Components - Other Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Sep. 30, 2020	Oct. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Apr. 30, 2019	Jul. 31, 2018	Aug. 31, 2017	Aug. 08, 2017
Balance Sheet Components [Line Items]
Common stock, shares issued	86,223,000	78,005,000		4,791,665	5,714,286			5,263,158	4,500,000
Amortization of debt discount and issuance cost	$ 149	$ 457	$ 391
Noncurrent assets	14,743	12,476
Evercord
Balance Sheet Components [Line Items]
Accounts receivable		5,782				$ 1,000
Estimated consideration		$ 15,377				15,400
Evercord | Contingent consideration
Balance Sheet Components [Line Items]
Total consideration						$ 4,700
Noncurrent assets
Balance Sheet Components [Line Items]
Debt discount	0
Long-term Debt
Balance Sheet Components [Line Items]
Debt discount	900
2017 Term Loan
Balance Sheet Components [Line Items]
Common stock, shares issued		25,000						25,000		300,000
Remaining borrowing capacity		$ 50,000								$ 50,000	$ 25,000
2017 Term Loan | Noncurrent assets
Balance Sheet Components [Line Items]
Debt instrument, fee amount										$ 1,200
BGI Genomics | Sequencing products and services
Balance Sheet Components [Line Items]
Noncurrent assets	$ 10,000						$ 10,000

Balance Sheet Components - Accr

Balance Sheet Components - Accrued Compensation (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Balance Sheet Components
Accrued paid time off	$ 2,260	$ 1,850
Accrued commissions	12,686	5,767
Accrued bonuses	9,635	5,710
Other accrued compensation	5,790	2,761
Total accrued compensation	$ 30,371	$ 16,088

Balance Sheet Components - Ot_2

Balance Sheet Components - Other Accrued Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Balance Sheet Components
Reserves for refunds to insurance carriers	$ 17,366	$ 9,410	$ 10,012
Accrued charges for third-party testing	5,141	8,408
Testing and laboratory materials from suppliers	2,720	4,301
Marketing and corporate affairs	3,325	2,957
Legal, audit and consulting fees	4,189	2,873
Accrued shipping charges	1,604	305
Sales tax payable	1,723	1,691
Accrued specimen service fees	2,355	2,269
Clinical trials and studies	2,353	1,092
Operating lease liabilities, current portion	7,300	5,739
Fixed asset purchases	1,691	1,482
Other accrued interest	1,078
Other accrued expenses	9,562	8,516
Total other accrued liabilities	$ 60,407	$ 49,043

Balance Sheet Components - Rese

Balance Sheet Components - Reserve Balance and Activities for Refunds (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Balance Sheet Components
Beginning balance	$ 9,410	$ 10,012
Additional reserves	19,427	9,560
Refunds to carriers	(6,066)	(7,752)
Reserves released to revenue	(5,405)	(2,410)
Ending balance	$ 17,366	$ 9,410

Leases (Details)

Leases (Details) $ in Thousands	1 Months Ended	12 Months Ended
	Jan. 31, 2021USD ($)	Dec. 31, 2020USD ($)ft²location	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Feb. 28, 2021ft²
Lessee, Lease, Description [Line Items]
Operating lease liabilities, current portion included in other accrued liabilities		$ 7,300	$ 5,739
Operating lease liabilities, long-term portion		21,246	$ 26,297
Operating lease liabilities		$ 28,546
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]		us-gaap:OtherCurrentLiabilitiesMember	us-gaap:OtherCurrentLiabilitiesMember
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]		us-gaap:OtherNoncurrentLiabilitiesMember	us-gaap:OtherNoncurrentLiabilitiesMember
Noncash investing activities related to right-of-use assets		$ 2,400
Weighted average remaining lease term		2 years 3 months 10 days
Weighted average discount rate (as a percent)		10.68%
Lease expense		$ 7,800	$ 7,800	$ 7,400
Impairment of right-of-use assets			400
Operating lease payments		$ 9,000	$ 8,600	$ 7,900
Corporate Headquarters Lease
Lessee, Lease, Description [Line Items]
Office space (area) | ft²		113,000
Number of office space locations | location		2
Term of lease		84 months
Renewal term of lease		5 years
"First Space" Sublease
Lessee, Lease, Description [Line Items]
Office space (area) | ft²		88,000
"Second Space" Sublease
Lessee, Lease, Description [Line Items]
Office space (area) | ft²		25,000
Corporate Headquarters Lease Amendment | Subsequent Event
Lessee, Lease, Description [Line Items]
Renewal term of lease	48 months
Lease expense	$ 9,300
Austin TX, Long-term Lease
Lessee, Lease, Description [Line Items]
Office space (area) | ft²		94,000
Term of lease		132 months
Tukwila, WA Lease
Lessee, Lease, Description [Line Items]
Office space (area) | ft²		10,000
Term of lease		62 months
Renewal term of lease		5 years
San Carlos, CA Lease
Lessee, Lease, Description [Line Items]
Office space (area) | ft²		25,879
Term of lease		48 months
Lease expense		$ 1,900
San Carlos, CA Lease | Subsequent Event
Lessee, Lease, Description [Line Items]
Office space (area) | ft²					22,405
San Carlos, CA Lease | Subsequent Event | Rentable square feet returned in lease amendment
Lessee, Lease, Description [Line Items]
Office space (area) | ft²					3,474
South San Francisco, CA Lease
Lessee, Lease, Description [Line Items]
Office space (area) | ft²		11,395
Term of lease		36 months
Lease expense		$ 900

Leases - Payments (Details)

Leases - Payments (Details) $ in Thousands	Dec. 31, 2020USD ($)
Leases
2021	$ 9,958
2022	10,242
2023	8,670
2024	2,400
2025	2,447
2026 and thereafter	2,283
Total	36,000
Less: imputed interest	(7,454)
Operating lease liabilities	$ 28,546

Commitments and Contingencies_2

Commitments and Contingencies (Details) $ in Thousands	Jan. 20, 2021claim	Dec. 31, 2020USD ($)claim	Jun. 19, 2020claim	Jun. 01, 2020claim	Mar. 23, 2020claim	Mar. 26, 2019claim
Other commitments
Total commitments		$ 76,020
Laboratory instruments supplier
Other commitments
Total commitments		3,490
Material suppliers
Other commitments
Total commitments		17,280
Application service providers
Other commitments
Total commitments		39,425
Gene sequencing reagents and kits provider
Other commitments
Total commitments		135
Software development provider
Other commitments
Total commitments		4,000
Other material suppliers
Other commitments
Total commitments		11,690
Securities related claims
Other commitments
Estimate of possible loss		$ 2,500
CareDX Patent Case | Patent infringement
Other commitments
Number of claims | claim					3	2
ArcherDX Patent Case | Patent infringement
Other commitments
Number of claims | claim		4
Ravgen Patent Case | Patent infringement
Other commitments
Number of claims | claim				2
Progenity Patent Case | Patent infringement
Other commitments
Number of claims | claim			6
Inivita Patent Case | Patent infringement | Subsequent Event
Other commitments
Number of claims | claim	2

Stock-Based Compensation (Detai

Stock-Based Compensation (Details)	6 Months Ended				12 Months Ended
	Oct. 31, 2020USD ($)shares	Apr. 30, 2020USD ($)shares	Oct. 31, 2019USD ($)shares	Apr. 30, 2019USD ($)shares	Dec. 31, 2020USD ($)periodshares	Dec. 31, 2019USD ($)shares	Dec. 31, 2018USD ($)	Jun. 30, 2015shares
Stock Based Compensation
Shares granted					6,204,000
2015 Plan
Stock Based Compensation
Shares reserved for issuance					13,988,187			3,451,495
Shares reserved for issuance as a proportion common stock outstanding (as a percent)					4.00%
2015 Plan | Minimum
Stock Based Compensation
Shares reserved for issuance					3,500,000
Employee stock purchase plan
Stock Based Compensation
Shares reserved for issuance					2,184,963			893,548
Shares reserved for issuance as a proportion common stock outstanding (as a percent)					1.00%
Price in relation to fair market value of common stock on the date of grant, lower range limit (as a percent)					85.00%
Maximum number of shares a participant may receive during the period (in shares)					5,000
Maximum amount of award or purchase during a calendar year | $					$ 25,000
Maximum offering period, term					27 months
Number of expected offering periods each year | period					2
Offering period, expected term					6 months
Number of Shares Purchased	136,288	97,247	136,084	132,177
Total Proceeds | $	$ 4,052,000	$ 3,061,000	$ 2,176,000	$ 2,147,000
Maximum employee contribution of employee's cash compensation (as a percent)					15.00%
Employee stock purchase plan | Minimum
Stock Based Compensation
Shares reserved for issuance					880,000
Performance-based awards
Stock Based Compensation
Stock-based compensation expense | $					$ 17,200,000	$ 7,300,000
Employee and non-employee stock options
Stock Based Compensation
Stock-based compensation expense | $					$ 50,171,000	$ 28,624,000	$ 14,198,000
Shares available for issuance					3,466,000	6,416,000
Employee and non-employee stock options | 2015 Plan
Stock Based Compensation
Vesting period					4 years
Expiration period					10 years
Stock appreciation rights | 2015 Plan
Stock Based Compensation
Expiration period					10 years
Restricted stock units
Stock Based Compensation
Number of shares vested					1,100
Shares granted					3,102

Stock-Based Compensation - Stoc

Stock-Based Compensation - Stock Options (Details) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020USD ($)$ / sharesshares	Dec. 31, 2019USD ($)$ / sharesshares	Dec. 31, 2018USD ($)$ / shares
Stock Based Compensation
RSUs granted (in shares)	(6,204,000)
RSUs forfeited/cancelled (in shares)	436,000
Additional disclosures
RSUs granted, impact on shares available for grant pool, ratio	2
Employee and non-employee stock options
Stock Based Compensation
Shares available for grant, beginning balance	6,416,000
Additional shares authorized	3,120,000
Options granted (in shares)	(457,000)
Options forfeited (in shares)	155,000
Shares available for grant, end balance	3,466,000	6,416,000
Number of shares
Outstanding, beginning balance (in shares)	8,497,000
Options granted (in shares)	457,000
Options exercised (in shares)	(2,092,000)
Options forfeited (in shares)	(155,000)
Outstanding, end balance (in shares)	6,707,000	8,497,000
Exercisable (in shares)	5,080,000
Vested and expected to vest (in shares)	6,609,000
Weighted-Average Exercise Price
Outstanding, beginning balance (in dollars per share) | $ / shares	$ 10.39
Granted (in dollars per share) | $ / shares	27.67
Exercised (in dollars per share) | $ / shares	11.24
Forfeited (in dollars per share) | $ / shares	15.39
Outstanding, end balance (in dollars per share) | $ / shares	11.19	$ 10.39
Exercisable (in dollars per share) | $ / shares	9.04
Vested and expected to vest (in dollars per share) | $ / shares	$ 11.09
Additional disclosures
Weighted average contractual term, options outstanding	6 years 14 days	6 years 10 months 17 days
Exercisable (in years)	5 years 4 months 24 days
Vested and expected to vest (in years)	6 years 3 days
Aggregate intrinsic value, options outstanding | $	$ 592,468	$ 197,955
Aggregate intrinsic value, options exercisable | $	459,683
Aggregate intrinsic value, vested and expected to vest | $	584,396
Aggregate intrinsic value, options exercised | $	184,700	70,000	$ 25,600
Fair value, options vested | $	$ 52,500	$ 11,000	$ 11,300
Weighted-average grant date fair value, options granted | $ / shares	$ 27.70	$ 8.01	$ 4.85
Non-employee stock options
Stock Based Compensation
Options granted (in shares)	(45,577)
Number of shares
Options granted (in shares)	45,577
Additional disclosures
Options unvested (in shares)	5,366
Restricted stock units
Stock Based Compensation
RSUs granted (in shares)	(3,102)
RSUs forfeited/cancelled (in shares)	218

Stock-Based Compensation - Perf

Stock-Based Compensation - Performance-based Awards (Details) - USD ($) $ in Thousands	3 Months Ended							12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
RSUs Granted (in shares)								6,204,000
Performance-based awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense								$ 17,200	$ 7,300
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
RSUs Granted (in shares)								3,102
Vested (in shares)								1,100
Restricted stock units | Fair Market Value
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
RSUs Granted (in shares)	22,000	27,000	21,000	436,000		188,000
Vested (in shares)		5,000		4,000
Restricted stock units | Monte-Carlo
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
RSUs Granted (in shares)	32,000			300,000	50,000		300,000
Vested (in shares)				150,000	25,000		219,000
Employee and non-employee stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options Granted (in shares)								457,000
Stock-based compensation expense								$ 50,171	$ 28,624	$ 14,198
Employee and non-employee stock options | Black-Scholes Merton
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options Granted (in shares)		10,000		129,000
Options Vested (in shares)		10,000
Employee and non-employee stock options | Monte-Carlo
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options Granted (in shares)				150,000			200,000
Options Vested (in shares)				75,000			138,000

Stock-Based Compensation - Assu

Stock-Based Compensation - Assumptions (Details) - shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Performance-based awards
Valuation of Stock Option Grants to Employees
Expected term (years)		7 years 3 months
Expected volatility		50.00%
Expected volatility, minimum	55.00%
Expected volatility, maximum	65.00%
Risk free interest rate, minimum	0.54%	1.63%
Risk free interest rate, maximum	1.64%	2.61%
Performance-based awards | Minimum
Valuation of Stock Option Grants to Employees
Expected term (years)	5 years 3 months
Performance-based awards | Maximum
Valuation of Stock Option Grants to Employees
Expected term (years)	7 years 3 months
Employee and non-employee stock options
Stock Based Compensation
Options granted (in shares)	457,000
Employee stock options
Valuation of Stock Option Grants to Employees
Expected volatility, minimum	49.94%	42.53%	40.28%
Expected volatility, maximum	61.96%	45.84%	42.53%
Expected dividend yield	0.00%	0.00%	0.00%
Risk free interest rate, minimum	0.31%	1.60%	2.37%
Risk free interest rate, maximum	1.70%	2.60%	3.06%
Employee stock options | Minimum
Valuation of Stock Option Grants to Employees
Expected term (years)	5 years 2 months 19 days	5 years 2 months 23 days	5 years 2 months 26 days
Employee stock options | Maximum
Valuation of Stock Option Grants to Employees
Expected term (years)	10 years	10 years	5 years 7 months 13 days
Non-employee stock options
Stock Based Compensation
Options granted (in shares)	45,577
Options unvested (in shares)	5,366

Stock-Based Compensation - Rest

Stock-Based Compensation - Restricted Stock Units (Details)	12 Months Ended
	Dec. 31, 2020$ / sharesshares
Shares
Granted (in shares)	6,204,000
Canceled/Forfeited (in shares)	(436,000)
Restricted stock units
Shares
Balance (in shares)	2,404
Granted (in shares)	3,102
Vested (in shares)	(1,100)
Canceled/Forfeited (in shares)	(218)
Balance (in shares)	4,188
Weighted Average Grant Date Fair Value
Balance (in dollars per share) | $ / shares	$ 19.86
Granted (in dollars per share) | $ / shares	39.94
Vested (in dollars per share) | $ / shares	19.69
Canceled/Forfeited (in dollars per share) | $ / shares	24.70
Balance (in dollars per share) | $ / shares	$ 34.02

Stock-Based Compensation - Comp

Stock-Based Compensation - Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Employee and non-employee stock options
Stock based compensation expense
Options granted (in shares)	457,000
Stock-based compensation expense	$ 50,171	$ 28,624	$ 14,198
Unrecognized compensation expense	$ 118,400
Unrecognized compensation expense, weighted average period of recognition	2 years 10 months 24 days
Employee and non-employee stock options | Cost of revenues
Stock based compensation expense
Stock-based compensation expense	$ 1,691	937	569
Employee and non-employee stock options | Research and development
Stock based compensation expense
Stock-based compensation expense	11,424	5,354	4,043
Employee and non-employee stock options | Selling, general and administrative
Stock based compensation expense
Stock-based compensation expense	37,056	22,333	9,586
Employee stock options
Stock based compensation expense
Stock-based compensation expense	49,215	27,989	14,081
Employee stock options | Cost of revenues
Stock based compensation expense
Stock-based compensation expense	1,691	905	564
Employee stock options | Research and development
Stock based compensation expense
Stock-based compensation expense	10,777	5,354	4,043
Employee stock options | Selling, general and administrative
Stock based compensation expense
Stock-based compensation expense	$ 36,747	21,730	9,474
Non-employee stock options
Stock based compensation expense
Options granted (in shares)	45,577
Options unvested (in shares)	5,366
Stock-based compensation expense	$ 956	635	117
Non-employee stock options | Cost of revenues
Stock based compensation expense
Stock-based compensation expense		32	5
Non-employee stock options | Research and development
Stock based compensation expense
Stock-based compensation expense	647
Non-employee stock options | Selling, general and administrative
Stock based compensation expense
Stock-based compensation expense	$ 309	$ 603	$ 112

Debt (Details)

Debt (Details)	1 Months Ended	12 Months Ended
	Apr. 30, 2020USD ($)D	Dec. 31, 2020USD ($)D$ / sharesshares	Dec. 31, 2019USD ($)$ / sharesshares	Dec. 31, 2018USD ($)	Sep. 30, 2020shares	Oct. 31, 2019$ / sharesshares	Apr. 30, 2019$ / sharesshares	Jul. 31, 2018$ / sharesshares	Aug. 31, 2017USD ($)shares	Aug. 08, 2017USD ($)	Sep. 30, 2015USD ($)
Debt Instrument [Line Items]
Proceeds from Convertible Note, net of issuance costs		$ 278,316,000
Common Stock, Par or Stated Value Per Share | $ / shares		$ 0.0001	$ 0.0001
Issuance of common stock to Orbimed			$ 507,000
Common stock, shares issued | shares		86,223,000	78,005,000		4,791,665	5,714,286	5,263,158	4,500,000
Stock issued (in dollars per share) | $ / shares						$ 35	$ 19	$ 20
Equity component	$ 85,600,000
Debt, repayment amount		$ 79,200,000
Accrued Interest		1,078,000
Amortization of debt discount and issuance cost		149,000	$ 457,000	$ 391,000
Interest expense		15,082,000	10,693,000	10,476,000
Convertible Notes
Debt Instrument [Line Items]
Aggregate principal amount	$ 287,500,000	287,500,000
Per annum interest rate (as a percent)	2.25%
Interest expense		11,630,000
Unamortized debt discount		$ 8,625,000
Debt instrument, term		7 years
Effective interest rate (as a percent)		8.27%
Principal amount per convertible note	$ 1,000
Threshold business days | D	5
Conversion price (in dollars per share) | $ / shares		$ 38.79
Initial conversion rate		25.7785
Convertible to shares of common stock		7,411,704
Percentage of principal amount converted		100.00%
Carrying value		$ 202,493,000
Equity component	$ 85,600,000
Debt Instrument, debt discount, Equity Component		79,100,000
Debt Instrument, debt discount, Liability Component		5,600,000
Debt issuance costs		$ 558,000
Commencing after September 30, 2020 | Convertible Notes
Debt Instrument [Line Items]
Threshold trading days | D	30
Percentage of conversion price	130.00%
5 consecutive trading day period | Convertible Notes
Debt Instrument [Line Items]
Threshold trading days | D	5
Percentage of conversion price	98.00%
Redeemable for cash on or after May 2024 | Convertible Notes
Debt Instrument [Line Items]
Threshold trading days | D		30
Percentage of conversion price		130.00%
Percentage of principal amount converted		100.00%
Debt Component | Convertible Notes
Debt Instrument [Line Items]
Unamortized debt discount		$ 6,057,000
Debt issuance costs		$ 392,000
Measurement input, risk free interest rate
Debt Instrument [Line Items]
Debt Instrument, Measurement Input	7.832
Level 2
Debt Instrument [Line Items]
Fair value of liability	$ 201,900,000
Minimum | Commencing after September 30, 2020 | Convertible Notes
Debt Instrument [Line Items]
Threshold trading days | D	20
Minimum | Redeemable for cash on or after May 2024 | Convertible Notes
Debt Instrument [Line Items]
Threshold trading days | D		20
Line Of Credit-UBS
Debt Instrument [Line Items]
Maximum borrowing capacity											$ 50,000,000
Outstanding balance		$ 49,000,000
Interest expense		800,000	1,700,000	1,600,000
Interest paid		800,000	1,700,000	$ 1,500,000
Debt, interest accrued		$ 1,100,000
Line Of Credit-UBS | LIBOR
Debt Instrument [Line Items]
Spread on interest rate (as a percent)		1.10%
2017 Term Loan
Debt Instrument [Line Items]
Maximum borrowing capacity										$ 100,000,000
Outstanding balance										75,000,000
Remaining borrowing capacity			50,000,000						$ 50,000,000	$ 25,000,000
Interest expense		$ 2,500,000	$ 9,000,000
Unamortized debt discount		$ 2,091,000
Common stock, shares issued | shares			25,000				25,000		300,000
Debt, repayment amount	$ 79,200,000
Accrued Interest	$ 400,000
2017 Term Loan | Minimum
Debt Instrument [Line Items]
Remaining borrowing capacity			$ 25,000,000
2017 Term Loan | LIBOR
Debt Instrument [Line Items]
Spread on interest rate (as a percent)			8.75%
Base interest rate (as a percent)			1.00%
2017 Term Loan | LIBOR | Minimum borrowing capacity drawn
Debt Instrument [Line Items]
Spread on interest rate (as a percent)			8.25%
Base interest rate (as a percent)			1.00%
2017 Term Loan | Noncurrent assets
Debt Instrument [Line Items]
Debt instrument, fee amount									$ 1,200,000

Debt - Carrying Amount (Details

Debt - Carrying Amount (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Apr. 30, 2020
Debt Instrument [Line Items]
Loss on debt extinguishment	$ 5,848
2017 Term Loan
Debt Instrument [Line Items]
Debt principal balance	75,000	$ 75,000
Plus: early payment penalties	3,757	$ 3,800
Reacquisition price of debt	78,757
Less: unamortized debt discount	(2,091)
Net carrying amount	72,909
Loss on debt extinguishment	$ 5,848

Debt - Discount and Issuance Co

Debt - Discount and Issuance Costs (Details) - Convertible Notes $ in Thousands	Dec. 31, 2020USD ($)
Debt Discount	$ 8,625
Debt Issuance Cost	558
Total	9,183
Equity Component
Debt Discount	2,568
Debt Issuance Cost	166
Total	2,734
Debt Component
Debt Discount	6,057
Debt Issuance Cost	392
Total	$ 6,449

Debt - Convertible Notes Balanc

Debt - Convertible Notes Balances (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Apr. 30, 2020
Equity component, net of issuance costs		$ 85,600
Convertible Notes
Debt principal balance	$ 287,500
Unamortized debt discount and debt issuance cost	(85,007)
Net carrying amount	$ 202,493
Equity component, net of issuance costs		$ 85,600

Debt - Interest Expense Recogni

Debt - Interest Expense Recognized Related To Convertible Notes (Details) - Convertible Notes $ in Thousands	12 Months Ended
	Dec. 31, 2020USD ($)
Cash interest expense
Contractual interest expense	$ 4,582
Non-cash interest expense
Amortization of debt discount and debt issuance cost	7,048
Total interest expense	$ 11,630

Stockholders' Equity (Details)

Stockholders' Equity (Details) - USD ($) $ / shares in Units, $ in Thousands	Apr. 26, 2019	Sep. 30, 2020	Oct. 31, 2019	Apr. 30, 2019	Jul. 31, 2018	Aug. 31, 2017	Dec. 31, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2017	Aug. 08, 2017
Preferred stock, shares authorized								50,000,000
Preferred stock, shares issued								0
Preferred stock, shares outstanding								0
Common stock, shares authorized								750,000,000	750,000,000
Common stock, par value (in dollars per share)								$ 0.0001	$ 0.0001
Common stock, shares issued		4,791,665	5,714,286	5,263,158	4,500,000			86,223,000	78,005,000
Common stock, shares outstanding								86,223,000	78,005,000
Stock price (in dollars per share)		$ 60									$ 8.16
Issuance of common stock upon exercise of warrants (in shares)					332,896
Issuance of common stock upon exercise of warrants					$ 6,800		$ 6,762
Stock issued (in dollars per share)			$ 35	$ 19	$ 20
Payment of offering expenses	$ 600	$ 300	$ 400	$ 600	$ 500
Proceeds from issuance of common stock	$ 108,100	$ 271,000	$ 216,200	$ 108,100	$ 97,300
Option for additional shares
Common stock, shares issued	789,473		857,142		675,000
Common stock
Common stock, shares issued							62,083,000	86,223,000	78,005,000	54,040,000
Issuance of common stock in exchange for commitment to provide debt financing (in shares)						300,000,000
Issuance of common stock in exchange for commitment to provide debt financing						$ 2,400
Issuance of common stock upon exercise of warrants (in shares)							333,000

Disposal of Business (Details)

Disposal of Business (Details) - USD ($) $ in Thousands	12 Months Ended		24 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2020	Sep. 30, 2019	Sep. 11, 2019
Gain from disposal of business	$ 14,388
Impairment	1,671	$ 1,544
Impairment of leasehold improvements	1,200
Impairment of capitalized software	100
Impairment of right-of-use asset	400
Exit or disposal activity			$ 400
Termination benefits	100
Early contract termination fee			$ 300
Selling, general and administrative
Impairment	1,700
Evercord
Estimated consideration	15,377			$ 15,400
Cash consideration				9,700
Accounts receivable	5,782			1,000
Assets	6,201
Deferred revenues					$ 5,200
Gain from disposal of business	$ 14,388
Contingent consideration | Evercord
Total consideration				$ 4,700

Disposal of Business - Summary

Disposal of Business - Summary of Gain from Disposal (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019
Net gain realized on disposal	$ 14,388
Evercord
Proceeds on disposal:	15,377	$ 15,400
Accounts receivable, net	5,782	$ 1,000
Equipment and inventory	419
Total assets sold	6,201
Deferred revenues	5,212
Net assets and liabilities sold	989
Net gain realized on disposal	$ 14,388

Income Taxes - Effective Tax Ra

Income Taxes - Effective Tax Rates (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Effective tax rates differing from U.S. federal statutory rate
U.S. Federal taxes (benefit) at statutory rate	$ (48,226,000)	$ (25,794,000)	$ (26,800,000)
State tax expense	(10,672,000)	(6,607,000)	(4,468,000)
Research and development credits	(3,964,000)	(1,645,000)	(1,164,000)
Stock-based compensation	(23,791,000)	(7,544,000)	(3,148,000)
Mark to market fair value adjustments			865,000
Nondeductible settlement for claims			1,000
Foreign tax	55,000	1,612,000	195,000
Other nondeductible items	9,776,000	1,378,000	690,000
Change in valuation allowance	76,920,000	40,599,000	34,150,000
Provision for income taxes	$ 98,000	$ 1,999,000	$ 321,000
U.S. Federal taxes (benefit) at statutory rate (as a percent)	(21.00%)	(21.00%)	(21.00%)
State tax expense (as a percent)	(4.65%)	(5.38%)	(3.50%)
Research and development credits (as a percent)	(1.73%)	(1.34%)	(0.91%)
Stock-based compensation (as a percent)	(10.36%)	(6.14%)	(2.47%)
Change in federal tax rate	0.00%	0.00%	0.00%
Mark to market fair value adjustments (as a percent)	0.00%	0.00%	0.68%
Nondeductible settlement for claims (as a percent)	0.00%	0.00%	0.00%
Foreign tax differential (as a percent)	0.02%	1.31%	0.15%
Other nondeductible items (as a percent)	4.26%	1.12%	0.54%
Change in valuation allowance (as a percent)	33.50%	33.06%	26.76%
Provision for income taxes (as a percent)	0.04%	1.63%	0.25%
Income tax expense	$ 98,000	$ 1,999,000	$ 321,000
Foreign withholding tax expense		1,900,000
Foreign income tax expense		100,000	200,000
State income tax expense	9,000	$ 40,000	$ 100,000
Clinical testing and software licensing
Effective tax rates differing from U.S. federal statutory rate
Foreign income tax expense	$ 100,000

Income Taxes - Deferred Income

Income Taxes - Deferred Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Taxes
Valuation allowance	$ 222,521	$ 163,040
Effect Of Tax Cuts And Jobs Act Of 2017 [Abstract]
Corporate tax rate	21.00%	21.00%	21.00%
Deferred tax assets
Net operating loss carryforwards	$ 177,899	$ 124,777
Research and development tax credit carryforwards	24,332	18,189
Reserves and accruals	21,770	10,002
Lease Liabilities	7,123	7,838
Deferred revenue	6,386	3,288
Stock based compensation	10,673	6,106
Total deferred tax assets before valuation allowance	248,183	170,200
Less: valuation allowance	(222,521)	(163,040)
Deferred tax assets, net	25,662	7,160
Deferred tax liabilities
Convertible debt	(19,143)
Right-of-use lease assets	(6,519)	(7,160)
Net deferred tax assets

Income Taxes - Net Operating Lo

Income Taxes - Net Operating Loss Carryforwards (Details) $ in Millions	Dec. 31, 2020USD ($)
Federal
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	$ 727.2
State
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	$ 412.9

Income Taxes - Tax Credit Carry

Income Taxes - Tax Credit Carryforwards (Details) $ in Millions	Dec. 31, 2020USD ($)
Tax Credit Carryforward [Line Items]
Taxable income required for full realization of deferred tax assets	$ 882.4
Federal | Research and development tax credit carryforward
Tax Credit Carryforward [Line Items]
Tax credit carryforward	21.4
Federal | Tax credit that can be carried forward indefinitely
Tax Credit Carryforward [Line Items]
Tax credit carryforward	407.3
State | Research and development tax credit carryforward
Tax Credit Carryforward [Line Items]
Tax credit carryforward	$ 16.9

Income Taxes - Unrecognized Tax

Income Taxes - Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Taxes [Line Items]
Interest and penalties accrued	$ 0
Reconciliation of the beginning and ending amount of gross unrecognized tax benefits
Balance at beginning of year	8,619	$ 7,362	$ 5,945
Additions based on tax positions related to the current year	2,889	1,426	1,416
(Reductions) for tax positions of prior years	(8)	(169)
Additions for tax positions of prior years			1
Balance at end of year	11,500	8,619	7,362
Research and development tax credit carryforward
Income Taxes [Line Items]
Unrecognized tax benefits increase	$ 2,900	$ 1,300	$ 1,400

Net Loss per Share - Loss per S

Net Loss per Share - Loss per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Numerator:
Net loss used to compute net loss per share, basic and diluted	$ (229,743)	$ (124,827)	$ (128,154)
Denominator:
Weighted-average number of shares used in computing net loss per share, basic and diluted	81,011	69,555	57,848
Net loss per share, basic and diluted (in dollars per share)	$ (2.84)	$ (1.79)	$ (2.22)
Potentially dilutive shares not included in diluted per share calculation	18,343	10,933	10,589
Convertible Notes
Denominator:
Convertible, If-converted value in excess of principal	$ 388,400
Potentially dilutive shares not included in diluted per share calculation	7,411

Net Loss per Share - Potentiall

Net Loss per Share - Potentially Dilutive Shares (Details) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially dilutive shares not included in diluted per share calculation	18,343	10,933	10,589
Employee and non-employee stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially dilutive shares not included in diluted per share calculation	6,707	8,497	9,463
Restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially dilutive shares not included in diluted per share calculation	4,188	2,404	1,084
Employee stock purchase plan
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially dilutive shares not included in diluted per share calculation	37	32	42
Convertible Notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially dilutive shares not included in diluted per share calculation	7,411