Guardant Health (GH) 10-Q 5 Aug 21 2021 Q2 Quarterly report Financial data

Cover Page

Cover Page - shares	6 Months Ended
	Jun. 30, 2021	Jul. 30, 2021
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Jun. 30, 2021
Document Transition Report	false
Entity File Number	001-38683
Entity Registrant Name	GUARDANT HEALTH, INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	45-4139254
Entity Address, Address Line One	505 Penobscot Dr.
Entity Address, City or Town	Redwood City
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94063
City Area Code	855
Local Phone Number	698-8887
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
Entity Shell Company	false
Title of 12(b) Security	Common Stock, par value $0.00001
Trading Symbol	GH
Security Exchange Name	NASDAQ
Entity Common Stock, Shares Outstanding		101,298,669
Amendment Flag	false
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q2
Entity Central Index Key	0001576280
Current Fiscal Year End Date	--12-31

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets (unaudited) - USD ($) $ in Thousands		Jun. 30, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents		$ 938,590	$ 832,977
Short-term marketable securities		853,072	961,903
Accounts receivable, net		53,667	53,299
Inventory		26,494	22,716
Prepaid expenses and other current assets, net		19,236	17,466
Total current assets		1,891,059	1,888,361
Long-term marketable securities		55,368	246,597
Property and equipment, net		89,737	62,782
Right-of-use assets		200,958	37,343
Intangible assets, net		15,189	16,155
Goodwill		3,290	3,290
Other assets, net		36,284	17,253
Total Assets	[1]	2,291,885	2,271,781
Current liabilities:
Accounts payable		21,399	7,340
Accrued compensation		34,735	28,280
Accrued expenses		31,998	22,639
Deferred revenue		8,480	8,550
Total current liabilities		96,612	66,809
Convertible senior notes, net		1,133,539	806,292
Long-term operating lease liabilities		211,783	41,565
Other long-term liabilities		2,486	1,520
Total Liabilities	[1]	1,444,420	916,186
Redeemable noncontrolling interest		59,400	57,100
Stockholders’ equity:
Common stock, par value of $0.00001 per share; 350,000,000 shares authorized as of June 30, 2021 and December 31, 2020; 101,265,100 and 100,213,985 shares issued and outstanding as of June 30, 2021 and December 31, 2020, respectively		1	1
Additional paid-in capital		1,597,419	1,902,389
Accumulated other comprehensive income		33	2,697
Accumulated deficit		(809,388)	(606,592)
Total Stockholders’ Equity		788,065	1,298,495
Total Liabilities, Redeemable Noncontrolling Interest and Stockholders’ Equity		$ 2,291,885	$ 2,271,781
[1]	As of June 30, 2021 and December 31, 2020, this balance includes $27.5 million and $35.0 million of assets, respectively, that can be used only to settle obligations of the consolidated variable interest entity (“VIE”) and VIE’s subsidiaries, and $3.8 million and $4.9 million, respectively, of liabilities of the consolidated VIE and VIE’s subsidiaries, for which their creditors do not have recourse to the general credit of the Company. See Note 3, Investment in Joint Venture .

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (unaudited) (Parenthetical) - USD ($) $ in Thousands		Jun. 30, 2021	Dec. 31, 2020
Common stock, par value (in usd per share)		$ 0.00001	$ 0.00001
Common stock, shares authorized (in shares)		350,000,000	350,000,000
Common stock, shares outstanding (in shares)		101,265,100	100,213,985
Common stock, shares issued (in shares)		101,265,100	100,213,985
Assets	[1]	$ 2,291,885	$ 2,271,781
Liabilities	[1]	1,444,420	916,186
Variable Interest Entity
Assets		27,500	35,000
Liabilities		$ 3,800	$ 4,900
[1]	As of June 30, 2021 and December 31, 2020, this balance includes $27.5 million and $35.0 million of assets, respectively, that can be used only to settle obligations of the consolidated variable interest entity (“VIE”) and VIE’s subsidiaries, and $3.8 million and $4.9 million, respectively, of liabilities of the consolidated VIE and VIE’s subsidiaries, for which their creditors do not have recourse to the general credit of the Company. See Note 3, Investment in Joint Venture .

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations (unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Revenue:
Precision oncology testing	$ 72,604	$ 50,991	$ 136,333	$ 111,237
Development services and other	19,497	15,344	34,433	22,608
Total revenue	92,101	66,335	170,766	133,845
Costs and operating expenses:
Cost of precision oncology testing	24,887	17,809	48,477	36,000
Cost of development services and other	5,040	4,626	10,197	6,941
Research and development expense	63,724	36,319	119,232	73,335
Sales and marketing expense	47,716	25,015	82,054	50,130
General and administrative expense	48,376	37,186	116,311	56,971
Total costs and operating expenses	189,743	120,955	376,271	223,377
Loss from operations	(97,642)	(54,620)	(205,505)	(89,532)
Interest income	1,037	2,640	2,588	5,958
Interest expense	(644)	(10)	(1,290)	(22)
Other income (expense), net	(243)	2,285	(533)	2,076
Loss before provision for income taxes	(97,492)	(49,705)	(204,740)	(81,520)
Provision for income taxes	83	34	193	48
Net loss	(97,575)	(49,739)	(204,933)	(81,568)
Adjustment of redeemable noncontrolling interest	0	(4,900)	(2,300)	(800)
Net loss attributable to Guardant Health, Inc. common stockholders	(97,575)	(54,639)	(207,233)	(82,368)
Net loss attributable to Guardant Health, Inc. common stockholders	$ (97,575)	$ (54,639)	$ (207,233)	$ (82,368)
Net loss per share attributable to Guardant Health, Inc. common stockholders, basic (in usd per share)	$ (0.96)	$ (0.57)	$ (2.05)	$ (0.87)
Net loss per share attributable to Guardant Health, Inc. common stockholders, diluted (in usd per share)	$ (0.96)	$ (0.57)	$ (2.05)	$ (0.87)
Weighted-average shares used in computing net loss per share attributable to Guardant Health, Inc. common stockholders, basic (in shares)	101,172	96,011	101,064	95,196
Weighted-average shares used in computing net loss per share attributable to Guardant Health, Inc. common stockholders, diluted (in shares)	101,172	96,011	101,064	95,196

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Comprehensive Loss (unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Statement of Comprehensive Income [Abstract]
Net loss	$ (97,575)	$ (49,739)	$ (204,933)	$ (81,568)
Other comprehensive income (loss), net of tax impact:
Unrealized gain (loss) on available-for-sale securities	(878)	(2,338)	(1,584)	4,233
Foreign currency translation adjustments	7	25	(1,080)	48
Other comprehensive income (loss)	(871)	(2,313)	(2,664)	4,281
Comprehensive loss	(98,446)	(52,052)	(207,597)	(77,287)
Comprehensive income (loss) attributable to redeemable noncontrolling interest	0	(4,900)	(2,300)	(800)
Comprehensive loss attributable to Guardant Health, Inc.	$ (98,446)	$ (56,952)	$ (209,897)	$ (78,087)

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Redeemable Noncontrolling Interest and Stockholders’ Equity (unaudited) - USD ($) $ in Thousands	Total	Cumulative effect adjustment for ASU 2020-06 adoption	Redeemable Noncontrolling Interest	Common Stock	Additional Paid-in Capital	Additional Paid-in CapitalCumulative effect adjustment for ASU 2020-06 adoption	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit	Accumulated DeficitCumulative effect adjustment for ASU 2020-06 adoption
Beginning balance at Dec. 31, 2019			$ 49,600
Increase (Decrease) in Temporary Equity [Roll Forward]
Adjustment of redeemable noncontrolling interest	$ (800)		800					$ (800)
Ending balance at Jun. 30, 2020			50,400
Beginning balance (in shares) at Dec. 31, 2019				94,261,414
Beginning balance at Dec. 31, 2019	798,393			$ 1	$ 1,150,090		$ 1,111	(352,809)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock in public offering, net of offering costs (in shares)				4,312,500
Issuance of common stock in public offering, net of offering costs	354,600				354,600
Issuance of common stock upon exercise of stock options (in shares)				654,557
Issuance of common stock upon exercise of stock options	3,548				3,548
Vesting of restricted stock units (in shares)				25,602
Vesting of common stock exercised early	26				26
Common stock issued under employee stock purchase plan (in shares)				58,164
Common stock issued under employee stock purchase plan	3,956				3,956
Stock-based compensation	32,153				32,153
Other comprehensive gain (loss), net of tax impact	4,281						4,281
Net loss	(81,568)							(81,568)
Ending balance (in shares) at Jun. 30, 2020				99,312,237
Ending balance at Jun. 30, 2020	1,114,589			$ 1	1,544,373		5,392	(435,177)
Beginning balance at Mar. 31, 2020			45,500
Increase (Decrease) in Temporary Equity [Roll Forward]
Adjustment of redeemable noncontrolling interest	(4,900)		4,900					(4,900)
Ending balance at Jun. 30, 2020			50,400
Beginning balance (in shares) at Mar. 31, 2020				94,509,011
Beginning balance at Mar. 31, 2020	785,113			$ 1	1,157,945		7,705	(380,538)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock in public offering, net of offering costs (in shares)				4,312,500
Issuance of common stock in public offering, net of offering costs	354,600				354,600
Issuance of common stock upon exercise of stock options (in shares)				412,554
Issuance of common stock upon exercise of stock options	2,044				2,044
Vesting of restricted stock units (in shares)				20,008
Vesting of common stock exercised early	13				13
Common stock issued under employee stock purchase plan (in shares)				58,164
Common stock issued under employee stock purchase plan	3,956				3,956
Stock-based compensation	25,815				25,815
Other comprehensive gain (loss), net of tax impact	(2,313)						(2,313)
Net loss	(49,739)							(49,739)
Ending balance (in shares) at Jun. 30, 2020				99,312,237
Ending balance at Jun. 30, 2020	1,114,589			$ 1	1,544,373		5,392	(435,177)
Beginning balance at Dec. 31, 2020			57,100
Increase (Decrease) in Temporary Equity [Roll Forward]
Adjustment of redeemable noncontrolling interest	(2,300)		2,300					(2,300)
Ending balance at Jun. 30, 2021			59,400
Beginning balance (in shares) at Dec. 31, 2020				100,213,985
Beginning balance at Dec. 31, 2020	$ 1,298,495	$ (325,966)		$ 1	1,902,389	$ (330,403)	2,697	(606,592)	$ 4,437
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Accounting Standards Update [Extensible List]	gh:AccountingStandardsUpdate202006Member
Issuance of common stock upon exercise of stock options (in shares)	371,711			371,711
Issuance of common stock upon exercise of stock options	$ 5,388				5,388
Vesting of restricted stock units (in shares)				618,506
Vesting of common stock exercised early	26				26
Common stock issued under employee stock purchase plan (in shares)				60,898
Common stock issued under employee stock purchase plan	5,401				5,401
Taxes paid related to net share settlement of restricted stock units	(74,958)				(74,958)
Stock-based compensation	89,576				89,576
Other comprehensive gain (loss), net of tax impact	(2,664)						(2,664)
Net loss	(204,933)							(204,933)
Ending balance (in shares) at Jun. 30, 2021				101,265,100
Ending balance at Jun. 30, 2021	788,065			$ 1	1,597,419		33	(809,388)
Beginning balance at Mar. 31, 2021			59,400
Ending balance at Jun. 30, 2021			$ 59,400
Beginning balance (in shares) at Mar. 31, 2021				101,085,653
Beginning balance at Mar. 31, 2021	847,046			$ 1	1,557,954		904	(711,813)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options (in shares)				88,832
Issuance of common stock upon exercise of stock options	926				926
Vesting of restricted stock units (in shares)				29,717
Vesting of common stock exercised early	13				13
Common stock issued under employee stock purchase plan (in shares)				60,898
Common stock issued under employee stock purchase plan	5,401				5,401
Taxes paid related to net share settlement of restricted stock units	(1,382)				(1,382)
Stock-based compensation	34,507				34,507
Other comprehensive gain (loss), net of tax impact	(871)						(871)
Net loss	(97,575)							(97,575)
Ending balance (in shares) at Jun. 30, 2021				101,265,100
Ending balance at Jun. 30, 2021	$ 788,065			$ 1	$ 1,597,419		$ 33	$ (809,388)

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Redeemable Noncontrolling Interest and Stockholders’ Equity (unaudited) (Parenthetical) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2020
Statement of Stockholders' Equity [Abstract]
Adjustments to additional paid in capital, stock issued, issuance costs	$ 1,130	$ 1,130

Condensed Consolidated Statem_5

Condensed Consolidated Statements of Cash Flows (unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
OPERATING ACTIVITIES:
Net loss	$ (204,933)	$ (81,568)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	10,637	7,109
Non-cash operating lease costs	10,839	3,386
Charge of in-process research and development costs with no alternative future use	0	8,500
Re-valuation of contingent consideration	875	(190)
Non-cash stock-based compensation	89,576	32,153
Amortization of debt issuance costs	1,282	0
Amortization of premium (discount) on marketable securities	6,528	1,065
Other	8	(19)
Changes in operating assets and liabilities:
Accounts receivable, net	(368)	6,894
Inventory	(3,778)	(5,173)
Prepaid expenses and other current assets	(3,036)	438
Other assets	(4,282)	(242)
Accounts payable	7,112	(2,476)
Accrued compensation	6,455	(31)
Accrued expenses and other liabilities	7,304	(1,820)
Operating lease liabilities	(3,033)	(3,881)
Deferred revenue	(70)	(792)
Net cash used in operating activities	(78,884)	(36,647)
INVESTING ACTIVITIES:
Purchases of marketable securities	(126,163)	(465,302)
Maturity of marketable securities	418,110	197,548
Purchase of non-marketable equity and other related investments	(12,750)	0
Purchases of property and equipment	(28,261)	(19,105)
Purchase of intangible assets and capitalized license obligations	0	(17,886)
Net cash provided by (used in) investing activities	250,936	(304,745)
FINANCING ACTIVITIES:
Payments made on finance lease obligations	(91)	(79)
Proceeds from issuance of common stock upon exercise of stock options	5,388	3,548
Proceeds from issuances of common stock under employee stock purchase plan	5,401	3,956
Taxes paid related to net share settlement of restricted stock units	(74,958)	0
Proceeds from public offering, net of underwriting discounts and commissions	0	355,730
Payment of offering costs related to public offering	0	(369)
Payment of offering costs related to borrowings on convertible senior notes	(784)	0
Net cash (used in) provided by financing activities	(65,044)	362,786
Net effect of foreign exchange rate changes on cash, cash equivalents and restricted cash	(1,080)	49
Net increase in cash, cash equivalents and restricted cash	105,928	21,443
Cash and cash equivalents—Beginning of period	832,977	143,228
Cash, cash equivalents and restricted cash—End of period	938,905	164,671
Supplemental Disclosures of Cash Flow Information:
Operating lease liabilities arising from obtaining right-of-use assets	170,911	11,373
Supplemental Disclosures of Noncash Investing and Financing Activities:
Purchases of property and equipment included in accounts payable and accrued expenses	10,289	5,396
Issuance costs related to purchase of non-marketable equity and other related investments included in accounts payable and accrued expenses	587	0
Follow-on public offering issuance costs included in accounts payable and accrued expenses	0	761
Property and equipment acquired under finance leases	236	0
Reconciliation of cash, cash equivalents and restricted cash:
Cash and cash equivalents	938,590	164,671
Restricted cash – included in other assets, net	315	0
Total cash, cash equivalents and restricted cash	$ 938,905	$ 164,671

Description of Business

Description of Business	6 Months Ended
	Jun. 30, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Description of Business	Description of BusinessGuardant Health, Inc. (the “Company”) is a leading precision oncology company focused on helping conquer cancer globally through use of its proprietary tests, vast data sets and advanced analytics. The key to conquering cancer is unprecedented access to its molecular information throughout all stages of the disease, which the Company enables by a liquid or tissue biopsy. The Guardant Health Oncology Platform is designed to leverage the Company’s capabilities in technology, clinical development, regulatory and reimbursement to drive commercial adoption, accelerate drug development, improve patient clinical outcomes and lower healthcare costs. In pursuit of its goal to manage cancer across all stages of the disease, the Company provides its Guardant360, Guardant360 LDT, Guardant360 CDx, and GuardantOMNI liquid biopsy-based tests for advanced stage cancer. In February 2021, the Company launched its Guardant Reveal liquid biopsy-based tests for residual and recurring cancer to first address the need in Stage II-III colorectal cancer. In June 2021, the Company launched Guardant360 TissueNext, the Company's first tissue-based test which will be used to identify patients with advanced cancer who may benefit from biomarker-informed treatment, and Guardant360 Response which will be used to measure early indications to patients' response to treatment up to eight weeks earlier than response evaluation criteria in solid tumors. The Company is also developing tests from its LUNAR program which aims to address the needs of early stage cancer patients with neoadjuvant and adjuvant treatment selection, cancer survivors with surveillance, and asymptomatic individuals eligible for cancer screening and individuals at a higher risk for developing cancer with early detection. Using data collected from the Company's tests, the Company has also developed the GuardantINFORM platform to further accelerate precision oncology drug development by biopharmaceutical companies by offering them an in-silico research platform to further unlock insights into tumor evolution and treatment resistance across various biomarker-driven cancers. The Company was incorporated in Delaware in December 2011 and is headquartered in Redwood City, California. In May 2018, the Company formed and capitalized Guardant Health AMEA, Inc. (the “Joint Venture”) in the United States with an affiliate of SoftBank Vision Fund (AIV M1) L.P. (“SoftBank”). Under the terms of the joint venture agreement, the Company holds a 50% ownership interest in the Joint Venture. As of June 30, 2021, the Joint Venture has subsidiaries in Singapore and Japan (see Note 3, Investment in Joint Venture

Summary of Significant Accounti

Summary of Significant Accounting Policies	6 Months Ended
	Jun. 30, 2021
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies Basis of Presentation The Company’s condensed consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”). The accompanying condensed consolidated financial statements include the accounts of Guardant Health, Inc., its consolidated Joint Venture and majority owned subsidiary. Other stockholders’ interests in the Joint Venture are shown in the condensed consolidated financial statements as redeemable noncontrolling interest. All significant intercompany balances and transactions have been eliminated in consolidation. The Company believes that its existing cash and cash equivalents and marketable securities as of June 30, 2021, will be sufficient to allow the Company to fund its current operating plan through at least a period of one year after the date the accompanying condensed consolidated financial statements are issued. As the Company continues to incur losses, its transition to profitability is dependent upon a level of revenues adequate to support the Company’s cost structure. If the Company’s transition to profitability is not consistent with its current operating plan, the Company may have to seek additional capital. Use of Estimates The preparation of condensed consolidated financial statements in conformity with GAAP requires management to make certain estimates, judgments and assumptions that affect the reported amounts of assets and liabilities and the related disclosures at the date of the condensed consolidated financial statements, as well as the reported amounts of revenues and expenses during the periods presented. The Company bases its estimates on historical experience and other market-specific or other relevant assumptions that it believes to be reasonable under the circumstances. Estimates are used in several areas including, but not limited to, estimation of variable consideration, estimation of credit losses, standalone selling price allocation included in contracts with multiple performance obligations, goodwill and identifiable intangible assets, stock-based compensation, incremental borrowing rate for operating leases, contingencies, certain inputs into the provision for income taxes, including related reserves, valuation of non- marketable securities, valuation of redeemable noncontrolling interest, among others. These estimates generally involve complex issues and require judgments, involve the analysis of historical results and prediction of future trends, can require extended periods of time to resolve and are subject to change from period to period. Actual results may differ materially from management’s estimates. The extent to which the coronavirus 2019, or COVID-19 pandemic will ultimately impact the Company’s business, results of operations, financial conditions, or cash flows continues to be highly uncertain. The severity of the impact on the Company's business for the remainder of calendar year 2021 and beyond will depend on a number of factors, including, but not limited to, the duration and severity of the pandemic, and the impact of any variants of the virus, the extent and severity of the impact on the Company's customers and suppliers, the continued disruption to demand for the Company's products and services, and the impact of the global business and economic environment on liquidity and the availability of capital, all of which are uncertain and cannot be predicted. Unaudited Interim Condensed Financial Statements The accompanying condensed consolidated balance sheet as of June 30, 2021, the condensed consolidated statements of operations for the three and six months ended June 30, 2021, and 2020, the condensed consolidated statements of comprehensive loss for the three and six months ended June 30, 2021, and 2020, the condensed consolidated statements of redeemable noncontrolling interest and stockholders’ equity for the three and six months ended June 30, 2021, and 2020, and cash flows for the six months ended June 30, 2021, and 2020, and the related interim condensed consolidated disclosures are unaudited. The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with GAAP for interim financial information and in accordance with the instructions to Form 10-Q and Rule 10-01 of Regulation S-X of the Securities Act of 1933, as amended (the “Securities Act”). Accordingly, they do not include all of the information and notes required by GAAP for complete financial statements. These unaudited condensed consolidated financial statements include all adjustments, consisting only of normal recurring accruals that the Company believes are necessary to fairly state the financial position and the results of the Company’s operations and cash flows for interim periods in accordance with GAAP. Interim-period results are not necessarily indicative of results of operations or cash flows for a full year or any subsequent interim period. The accompanying condensed consolidated financial statements should be read in conjunction with the Company’s audited financial statements and notes thereto included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2020. Foreign Currency The functional currency of the subsidiaries of the consolidated Joint Venture is the local currency. The assets and liabilities of the subsidiaries are translated into U.S. dollars at exchange rates in effect at each balance sheet date, with the resulting translation adjustments recorded to a separate component of accumulated other comprehensive loss within stockholders’ equity. Income and expense accounts are translated at average exchange rates during the period. Foreign currency transaction gains and losses resulting from transactions denominated in a currency other than the functional currency are recognized in the condensed consolidated statements of operations. For the three and six months ended June 30, 2021, and 2020, foreign currency transaction gains and losses were immaterial. Restricted Cash Restricted cash consists of payroll withholding related to the Company's enrollment in certain voluntary disability insurance plan. Restricted cash balance as of June 30, 2021, was $0.3 million, which was included in other assets in the accompanying consolidated balance sheets. The Company did not have any restricted cash as of December 31, 2020. Non-Marketable Securities The Company acquires certain equity investments in private companies to promote business and strategic objectives. The Company's investments in non-marketable equity securities do not give the Company the ability to control or exercise significant influence over the investee. The Company's non-marketable equity and other related investments totaled $13.3 million as of June 30, 2021, and are included in other assets, net on the accompanying condensed consolidated balance sheets. The Company did not have such non-marketable equity and other related investments as of December 31, 2020. Non-marketable securities are subject to periodic impairment reviews and adjustments for observable price changes from orderly transactions. The Company's evaluation of impairment of such non-marketable securities is based on adverse changes in market conditions and the regulatory or economic environment, qualitative and quantitative analysis of the operating performance of the investee; changes in operating structure or management of the investee; additional funding requirements; and the investee’s ability to remain in business. Pursuant to one of the investments in non-marketable securities purchased by the Company, and subject to the Company purchasing additional non-marketable securities from the same investee, the Company acquired rights to purchase the investee at a pre-determined price subject to additional adjustments based on the performance of the investee, on or before December 31, 2022. As of June 30, 2021, no impairment or adjustments to carrying value of non-marketable securities have been recorded. The Company’s assessment of these factors in determining whether an impairment exists could change in the future due to new developments or changes in applied assumptions. Concentration of Risk The Company is subject to credit risk from its portfolio of cash equivalents held at one commercial bank and investments in marketable securities. The Company limits its exposure to credit losses by investing in money market funds through a U.S. bank with high credit ratings. The Company’s cash may consist of deposits held with banks that may at times exceed federally insured limits, however, its exposure to credit risk in the event of default by the financial institution is limited to the extent of amounts recorded on the condensed consolidated balance sheets. The Company performs evaluations of the relative credit standing of these financial institutions to limit the amount of credit exposure. The Company also invests in investment-grade debt instruments and has policy limits for the amount it can invest in any one type of security, except for securities issued or guaranteed by the U.S. government. The goals of the Company’s investment policy, in order of priority, are as follows: safety and preservation of principal and diversification of risk; liquidity of investments sufficient to meet cash flow requirements; and a competitive after-tax rate of return. Under its investment policy, the Company limits amounts invested in such securities by credit rating, maturity, investment type and issuer, as a result, the Company is not exposed to any significant concentrations of credit risk from these financial instruments. The Company is subject to credit risk from its accounts receivable. The majority of the Company’s accounts receivable arises from the provision of precision oncology services and development services and other in the United States and are primarily with biopharmaceutical companies with high credit ratings. The Company has not experienced any material losses related to receivables from individual customers, or groups of customers. The Company does not require collateral. Accounts receivable are recorded at net amount. A significant customer is a biopharmaceutical customer or a clinical testing payer that represents 10% or more of the Company’s total revenue or accounts receivable balance. Revenue attributable to each significant customer, including its affiliated entities, as a percentage of the Company’s total revenue, for the respective period, and accounts receivable balance attributable to each significant customers, including its affiliated entities, as a percentage of the Company’s total accounts receivable balance, at the respective condensed consolidated balance sheet date, are as follows: Revenue Accounts Receivable, Net Three Months Ended June 30, Six Months Ended June 30, June 30, 2021 December 31, 2020 2021 2020 2021 2020 (unaudited) (unaudited) Customer A * * * 14 % * 11 % Customer B 29 % 23 % 27 % 21 % * 13 % Customer C * 10 % * * * 12 % Customer D * * * * 16 % 11 % * less than 10% The Company is also subject to credit risk from its other receivables and other assets. The Company's other receivables and other assets include payments due from a third-party in relation to the settlement of a patent dispute reached in August 2020 for $8.0 million payable over a period of 6 years. In December 2020, the Company received the first installment payment of $1.0 million. The Company has evaluated and recorded a credit loss for the remaining $7.0 million considering the third-party's credit worthiness and lack of financial history. The following table presents the receivable and the related credit loss amounts: Gross Amount Allowance for Credit Losses Net Amount June 30, 2021 December 31, 2020 Three and Six Months Ended June 30, 2021 June 30, 2021 December 31, 2020 Beginning Balance Charged to (Reversed from) Other Income (Expense), Net Reclassi-fication Ending Balance (unaudited) (unaudited) (unaudited) (in thousand) Prepaid expenses and other current assets $ 1,100 $ — $ — $ — $ (1,100) $ (1,100) $ — $ — Other assets 5,900 7,000 (7,000) — 1,100 (5,900) — $ — Accounts Receivable, Net Accounts receivable represent valid claims against biopharmaceutical companies, research institutes and international distributors. The Company evaluates the collectability of its accounts receivable based on historical collection trends, the financial condition of payment partners, and external market factors and provides for an allowance for potential credit losses based on management’s best estimate of the amount of probable credit losses. As of June 30, 2021, and December 31, 2020, the Company had immaterial allowance for credit losses related to its accounts receivable. Contract assets are presented under accounts receivable, net and other assets, net on the Company’s condensed consolidated balance sheets and include balances from commercial and governmental payers. Contract assets consists primarily of: i) precision oncology testing revenues to clinical customers that are recognized upon delivery of the test results prior to cash collection; and ii) development services and other revenues to biopharmaceutical customers that are recognized upon the achievement of performance-based milestones but prior to the establishment of billing rights. Contract assets are relieved when the Company receives payments from clinical customers, or when it invoices the biopharmaceutical customers when milestones are achieved, thereby reclassifying the balances from contract assets to accounts receivable. As of June 30, 2021, the Company had contract assets of $24.8 million which was recorded in accounts receivable, net. As of December 31, 2020, the Company had contract assets of $15.6 million which was recorded in accounts receivable, net, which included $8.4 million of unbilled receivable relating to Guardant360 CDx. Asset Acquisition If an acquisition of an asset or group of assets does not meet the definition of a business, the transaction is accounted for as an asset acquisition rather than a business combination. An asset acquisition does not result in the recognition of goodwill and transaction costs are capitalized as part of the cost of the asset or group of assets acquired. Transaction costs allocated to in-process research and development technology with no future alternate use is expensed as incurred. The total consideration is allocated to the various intangible assets acquired on a relative fair value basis. Cash paid in connection of purchase of in-process research and development technology in an asset acquisition is presented within the investing section of the condensed consolidated statement of cash flows. Goodwill and Intangible Assets, net Intangible assets related to in-process research and development costs (“IPR&D”) acquired in a business combination are considered to be indefinite-lived until the completion or abandonment of the associated research and development efforts. If and when development is complete, the associated assets would be deemed finite-lived and would then be amortized based on their respective estimated useful lives at that point in time. Prior to completion of the research and development efforts, the assets are considered indefinite-lived. During this period, the assets will not be amortized but will be tested for impairment on an annual basis and between annual tests if we become aware of any events occurring or changes in circumstances that would indicate a reduction in the fair value of the IPR&D projects below their respective carrying amounts. Goodwill represents the excess of the purchase price over the fair value of net identifiable assets and liabilities. Goodwill and IPR&D are not amortized but are tested for impairment at least annually during the fourth fiscal quarter, or if circumstances indicate their value may no longer be recoverable. The Company continues to operate in one segment, which is considered to be the sole reporting unit and, therefore, goodwill was tested for impairment at the enterprise level. As of June 30, 2021, there has been no impairment of goodwill or IPR&D. Intangible assets are carried at cost, net of accumulated amortization. The Company does not have intangible assets with indefinite useful lives other than goodwill and the acquired IPR&D. Amortization is recorded on a straight-line basis over the intangible asset's useful life, which is approximately 6—12 years. Leases The Company determines if an arrangement contains a lease at inception. Operating lease right-of-use (“ROU”) assets and operating leases liabilities are recognized based on the present value of the future minimum lease payments over the lease term at the commencement date. ROU assets also include any initial direct costs incurred and any lease payments made at or before the lease commencement date, less lease incentives received or receivable. The Company uses its incremental borrowing rate based on the information available at the commencement date in determining the lease liabilities, as the Company's leases generally do not provide an implicit rate. Lease terms may include options to extend or terminate when the Company is reasonably certain the option will be exercised. Lease expense is recognized on a straight-line basis over the lease term. The Company also has lease arrangements with lease and non-lease components. The Company elected the practical expedient not to separate non-lease components from lease components for the Company’s facility leases. The Company also elected to apply the short-term lease measurement and recognition exemption in which ROU assets and lease liabilities are not recognized for leases with terms of 12 months or less. Convertible Senior Notes In accounting for the issuance of the convertible senior notes, the Company separates the notes into 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, using a discounted cash flow model with a risk adjusted yield. The carrying amount of the equity component representing the conversion option is determined by deducting the fair value of the liability component from the par value of the notes as a whole. This difference represents a debt discount that is amortized to interest expense using the effective interest method over the term of the notes. The equity component is not remeasured as long as it continues to meet the conditions for equity classification. In accounting for the transaction costs related to the issuance of the notes, the Company allocated the total amount incurred to the liability and equity components based on their relative fair values. Transaction costs attributable to the liability component are netted with the liability component and amortized to interest expense using the effective interest method over the term of the notes. Transaction costs attributable to the equity component are netted with the equity component of the notes in additional paid-in capital in the condensed consolidated balance sheets. Starting January 1, 2021, upon early adoption of ASU 2020-06, Accounting for Convertible Instruments and Contracts in an Entity’s Own Equity, the carrying amount of the equity component of the cash conversion feature including the allocated debt issuance costs were reclassified from additional paid-in capital to convertible senior notes, net. Revenue Recognition The Company derives revenue from the provision of precision oncology testing services provided to its ordering physicians and biopharmaceutical customers, as well as from biopharmaceutical research and development services provided to its biopharmaceutical customers. Precision oncology testing services include genomic profiling and the delivery of other genomic information derived from the Company’s platform. Development services and other include companion diagnostic development, clinical trial setup, monitoring and maintenance, information solutions and laboratory services, and other miscellaneous revenue streams. The Company currently receives payments from third-party commercial and governmental payers, certain hospitals and oncology centers and individual patients, as well as biopharmaceutical companies, research institutes and international distributors. Revenues are recognized when control of services is transferred to customers, in an amount that reflects the consideration the Company expects to be entitled to in exchange for those services. ASC 606 provides for a five-step model that includes identifying the contract with a customer, identifying the performance obligations in the contract, determining the transaction price, allocating the transaction price to the performance obligations, and recognizing revenue when, or as, an entity satisfies a performance obligation. Precision oncology testing The Company recognizes revenue from the sale of its precision oncology tests for clinical customers, including certain hospitals, cancer centers, other institutions and patients, at the time results of the test are reported to physicians. Most precision oncology tests requested by clinical customers are sold without a written agreement; however, the Company determines an implied contract exists with its clinical customers. The Company identifies each sale of its liquid biopsy test to clinical customer as a single performance obligation. With the exception of certain limited contracted arrangements with insurance carriers and other institutions where the transaction price is fixed, a stated contract price does not exist and the transaction price for each implied contract with clinical customers represents variable consideration. The Company estimates the variable consideration under the portfolio approach and considers the historical reimbursement data from third-party commercial and governmental payers and patients, as well as known or anticipated reimbursement trends not reflected in the historical data. The Company monitors the estimated amount to be collected in the portfolio at each reporting period based on actual cash collections in order to assess whether a revision to the estimate is required. Both the estimate and any subsequent revision contain uncertainty and require the use of significant judgment in the estimation of the variable consideration and application of the constraint for such variable consideration. The Company analyzes its actual cash collections over the expected reimbursement period and compares it with the estimated variable consideration for each portfolio and any difference is recognized as an adjustment to estimated revenue after the expected reimbursement period, subject to assessment of the risk of future revenue reversal. For the three months ended June 30, 2021, and 2020, the Company recorded $9.6 million and $9.1 million as revenue, respectively, resulting from cash collections over the expected reimbursement period exceeding the estimated variable consideration related to samples processed in previous periods, including revenue received from successful appeals of reimbursement denials, net of recoupments. For the six months ended June 30, 2021, and 2020, the Company recorded $14.6 million and $16.5 million as revenue, respectively, resulting from cash collections over the expected reimbursement period exceeding the estimated variable consideration related to samples processed in previous periods, including revenue received from successful appeals of reimbursement denials, net of recoupments. Revenue from sales of precision oncology tests to biopharmaceutical customers are based on a negotiated price per test or on the basis of an agreement to provide certain testing volume over a defined period. The Company identifies its promise to transfer a series of distinct liquid biopsy tests to biopharmaceutical customers as a single performance obligation. Precision oncology tests to biopharmaceutical customers are generally billed at a fixed price for each test performed. For agreements involving testing volume to be satisfied over a defined period, revenue is recognized over time based on the number of tests performed as the performance obligation is satisfied over time. Results of the Company’s precision oncology services are delivered electronically, and as such there are no shipping or handling fees incurred by the Company or billed to customers. Development services and other The Company performs development services for its biopharmaceutical customers utilizing its precision oncology information platform. Development services typically represent a single performance obligation as the Company performs a significant integration service, such as analytical validation and regulatory submissions. The individual promises are not separately identifiable from other promises in the contracts and, therefore, are not distinct. However, under certain contracts, a biopharmaceutical customer may engage the Company for multiple distinct development services which are both capable of being distinct and separately identifiable from other promises in the contracts and, therefore, distinct performance obligations. The Company collaborates with pharmaceutical companies in the development of new drugs. As part of these collaborations, the Company provides services related to regulatory filings to support companion diagnostic device submissions for the Company’s liquid biopsy panels. Under these collaborations, the Company generates revenue from achievement of milestones, as well as provision of on-going support. For development services performed, the Company is compensated through a combination of an upfront fee and performance-based, non-refundable regulatory and other developmental milestone payments. The transaction price of the Company's development services contracts typically represents variable consideration. Application of the constraint for variable consideration to milestone payments is an area that requires significant judgment. The Company evaluates factors such as the scientific, clinical, regulatory, commercial, and other risks that must be managed to achieve the respective milestone and the level of effort and investment required to achieve the respective milestone. In making this assessment, the Company considers its historical experience with similar milestones, the degree of complexity and uncertainty associated with each milestone, and whether achievement of the milestone is dependent on parties other than the Company. The constraint for variable consideration is applied such that it is probable a significant reversal of revenue will not occur when the uncertainty associated with the contingency is resolved. Application of the constraint for variable consideration is assessed and updated at each reporting period as a revision to the estimated transaction price. The Company recognizes development services revenue over the period in which biopharmaceutical research and development services are provided. Specifically, the Company recognizes revenue using an input method to measure progress, utilizing costs incurred to-date relative to total expected costs as its measure of progress. The Company assesses the changes to the total expected cost estimates as well as any incremental fees negotiated resulting from changes to the scope of the original contract in determining the revenue recognition at each reporting period. For development of new products or services under these arrangements, costs incurred before technological feasibility is reached are included as research and development expenses in the Company’s condensed consolidated statements of operations, while costs incurred thereafter are recorded as cost of development services and other. The Company also has other miscellaneous revenue streams that are recognized in addition to development services noted above such as clinical trial setup, monitoring and maintenance, referral fees, liquid biopsy testing development and support, GuardantConnect, GuardantINFORM and Guardant-19, and kits fulfillment related revenues. Revenues related to clinical trial setup, monitoring and maintenance, referral fees, liquid biopsy testing development and support, GuardantConnect, GuardantINFORM are generally recognized over time based on an input method to measure progress in the period when the associated services have been performed. Guardant-19 and kits fulfillment related revenues are recognized when such products are delivered. Contracts with multiple performance obligations Contracts with biopharmaceutical customers may include multiple distinct performance obligations, such as provision of precision oncology testing, biopharmaceutical research and development services, and clinical trial enrollment assistance, among others. The Company evaluates the terms and conditions included within its contracts with biopharmaceutical customers to ensure appropriate revenue recognition, including whether services are considered distinct performance obligations that should be accounted for separately versus together. The Company first identifies material promises, in contrast to immaterial promises or administrative tasks, under the contract, and then evaluates whether these promises are both capable of being distinct and distinct within the context of the contract. In assessing whether a promised service is capable of being distinct, the Company considers whether the customer could benefit from the service either on its own or together with other resources that are readily available to the customer, including factors such as the research, development, and commercialization capabilities of a third party as well as the availability of the associated expertise in the general marketplace. In assessing whether a promised service is distinct within the context of the contract, the Company considers whether it provides a significant integration of the services, whether the services significantly modify or customize one another, or whether the services are highly interdependent or interrelated. For contracts with multiple performance obligations, the transaction price is allocated to the separate performance obligations on a relative standalone selling price basis. The Company determines standalone selling price by considering the historical selling price of these performance obligations in similar transactions as well as other factors, including, but not limited to, the price that customers in the market would be willing to pay, competitive pricing of other vendors, industry publications and current pricing practices, and expected costs of satisfying each performance obligation plus appropriate margin. Deferred revenue Deferred revenue, which is a contract liability, consists primarily of payments received in advance of revenue recognition from contracts with customers. For example, development services and other contracts with biopharmaceutical customers often contain upfront payments which results in the recording of deferred revenue to the extent cash is received prior to the Company's performance of the related services. Contract liabilities are relieved as the Company performs its obligations under the contract and revenue is consequently recognized. As of June 30, 2021, and December 31, 2020, the deferred revenue balance was $8.5 million and $8.6 million, respectively, which included $2.9 million and $3.0 million, respectively, related to collaboration development efforts with pharmaceutical companies to be recognized as the Company performs research and development services in the future periods. Revenue recognized in the six months ended June 30, 2021, that was included in the deferred revenue balance as of December 31, 2020, was $6.4 million, of which $3.0 million represented revenue from provision of development services under the collaboration agreements with biopharmaceutical customers. Revenue recognized in the six months ended June 30, 2020, that was included in the deferred revenue balance as of December 31, 2019, was $7.6 million, which primarily represented revenue from provision of development services under the collaboration agreements with biopharmaceutical customers. Transaction price allocated to the remaining performance obligations Transaction price allocated to remaining performance obligations represents contracted revenue that has not yet been recognized, which includes deferred revenue and non-cancelable amounts that will be invoiced and recognized as revenues in future periods. The Com

Investment in Joint Venture

Investment in Joint Venture	6 Months Ended
	Jun. 30, 2021
Equity Method Investments and Joint Ventures [Abstract]
Investment in Joint Venture	Investment in Joint Venture Variable Interest Entity (“VIE”) In May 2018, the Company and an affiliate of SoftBank formed and capitalized the Joint Venture for the sale, marketing and distribution of the Company’s tests in all areas worldwide, outside of North America, Central America, South America, the United Kingdom, all other member states of the European Union as of May 9, 2017, Iceland, Norway, Switzerland and Turkey. The Company expects to rely on the Joint Venture to accelerate commercialization of its products in Asia, the Middle East and Africa. Under the terms of the joint venture agreement, the Company paid $9.0 million for 40,000 shares of common stock, or 50% ownership interest, of the Joint Venture, and the affiliate of SoftBank contributed $41.0 million for 40,000 shares of common stock, or the other 50% ownership interest, of the Joint Venture. In June 2020, an amended and restated certificate of incorporation of the Joint Venture, as approved by the board of directors of the Joint Venture, was filed with the Secretary of State of the State of Delaware. The amended and restated certificate of incorporation, among other things, increased the number of authorized shares of common stock to 89,000,000 shares consisting of 80,000,000 shares of Class A common stock and 9,000,000 shares of Class B (non-voting) common stock; and authorized 80,000,000 shares of Series A preferred stock. Pursuant to the amended and restated certificate of incorporation, each share of common stock held by the Company and the affiliate of SoftBank was reclassified and exchanged for 1,000 shares of Series A preferred stock. As a result, each of the Company and the affiliate of SoftBank held 40,000,000 shares of Series A preferred stock. The holders of Series A preferred stock are entitled to receive dividends at the rate of $0.05 per share if and when declared by the board of directors of the Joint Venture. In June 2020, the board of directors of the Joint Venture authorized the adoption of the Joint Venture’s 2020 Equity Incentive Plan pursuant to which 4,595,555 shares of Class B common stock have been reserved for issuance. As of June 30, 2021, and December 31, 2020, 91,109 and no shares of Class B common stock have been issued and outstanding, and no shares of Class A common stock have been issued and outstanding. As of June 30, 2021 and December 31, 2020, 80,000,000 shares of Series A preferred stock have been issued and outstanding. Under the terms of the joint venture agreement, neither party is obligated to make any further capital contribution, in cash or otherwise, to the Joint Venture. The Joint Venture is deemed to be a variable interest entity (“VIE”) and the Company has been identified as the VIE’s primary beneficiary. As the primary beneficiary, the Company has consolidated the financial position, results of operations and cash flows of the Joint Venture in its financial statements and all intercompany balances have been eliminated in consolidation. As of June 30, 2021, and December 31, 2020, the Joint Venture had total assets of approximately $27.5 million and $35.0 million, respectively, which were primarily comprised of cash, property and equipment, right-of-use assets and security deposits. Although the Company consolidates the Joint Venture, the legal structure of the Joint Venture limits the recourse that its creditors will have over the Company’s general credit or assets. Similarly, the assets held in the Joint Venture can be used only to settle obligations of the Joint Venture. As of June 30, 2021, the Company has not provided financial or other support to the Joint Venture that was not previously contracted or required. Put-call arrangements The joint venture agreement includes a put-call arrangement with respect to the shares of the Joint Venture held by SoftBank and its affiliates. Under certain specified circumstances and on terms specified in the joint venture agreement, including timely written notice, SoftBank has the right to cause the Company to purchase all shares of the Joint Venture held by SoftBank and its affiliates (the “put right”), and the Company has a right to purchase all such shares (the “call right”). Each of the Company and SoftBank may exercise its respective put-call rights for the Company to purchase all shares of the Joint Venture held by SoftBank in the event of (i) certain material disagreements relating to the Joint Venture or its business that may seriously affect the ability of the Joint Venture to perform its obligations under the joint venture agreement or may otherwise seriously impair the ability of the Joint Venture to conduct its business in an effective matter, other than one relating to the Joint Venture’s business plan or to factual matters that may be capable of expert determination; (ii) the effectiveness of the Company’s initial public offering, a change in control of the Company, the seventh anniversary of the formation of the Joint Venture, or each subsequent anniversary of each of the foregoing events; or (iii) a material breach of the joint venture agreement by the other party that goes unremedied within 20 business days. Unless the shares of the Joint Venture are publicly traded and listed on a nationally recognized stock exchange, the purchase price per share of the Joint Venture in these situations will be determined by a third-party valuation firm on the assumption that the sale is on an arm’s-length basis on the date of the put or call notice. The third-party valuation firm may evaluate a range of factors and employ assumptions that are subjective in nature, which could result in the fair value of SoftBank’s interests in the Joint Venture being determined to be materially different from what has been recorded in the Company’s condensed consolidated financial statements. In the event the Company exercises its call right, the fair value of the Joint Venture will be deemed to be no less than an amount that yields a 20% internal rate of return on each tranche of capital invested by SoftBank and its affiliates in the Joint Venture, taking into account all proceeds received by SoftBank and its affiliates arising from their shares through such date. In the event SoftBank exercises its put right and the fair value of the Joint Venture is determined to be greater than 40% of the fair value of the Company, the Company will only be required to purchase the number of shares of the Joint Venture held by SoftBank and its affiliates having an aggregate value equal to the product of 40% of the Company's fair value and the pro rata portion of the outstanding shares of the Joint Venture held by SoftBank and its affiliates. The Company may pay the purchase price for the shares of the Joint Venture in cash, in shares of its capital stock (which may be a non-voting security with senior preferences to all other classes of its equity or, if its common stock is publicly traded on a national exchange, its common stock), or in a combination thereof. In the event the Company exercises the call right, SoftBank will choose the form of consideration. In the event SoftBank exercises the put right, the Company will choose the form of consideration.

Condensed Consolidated Balanc_3

Condensed Consolidated Balance Sheet Components	6 Months Ended
	Jun. 30, 2021
Balance Sheet Related Disclosures [Abstract]
Condensed Consolidated Balance Sheet Components	Condensed Consolidated Balance Sheet Components Property and Equipment, Net Property and equipment, net consist of the following: June 30, 2021 December 31, 2020 (unaudited) (in thousands) Machinery and equipment $ 50,960 $ 40,216 Leasehold improvements 35,542 34,037 Computer hardware 15,929 10,862 Construction in progress 26,892 7,833 Furniture and fixtures 3,591 3,043 Computer software 1,094 1,136 Property and equipment, gross $ 134,008 $ 97,127 Less: accumulated depreciation (44,271) (34,345) Property and equipment, net $ 89,737 $ 62,782 Depreciation expense related to property and equipment was $5.1 million and $3.2 million for the three months ended June 30, 2021, and 2020, respectively, and $9.6 million and $6.2 million for the six months ended June 30, 2021, and 2020, respectively. Accrued Expenses Accrued expenses consist of the following: June 30, 2021 December 31, 2020 (unaudited) (in thousands) Operating lease liabilities $ 7,547 $ 6,632 Accrued tax liabilities 4,500 4,634 Accrued professional services 6,564 3,397 Accrued clinical trials and studies 2,625 1,264 Accrued legal expenses 2,081 2,875 Purchases of property and equipment included in accrued expenses 2,383 1,156 Accrued royalty obligations 179 146 Others 6,119 2,535 Total accrued expenses $ 31,998 $ 22,639

Fair Value Measurements, Cash E

Fair Value Measurements, Cash Equivalents and Marketable Securities	6 Months Ended
	Jun. 30, 2021
Fair Value Disclosures [Abstract]
Fair Value Measurements, Cash Equivalents and Marketable Securities	Fair Value Measurements, Cash Equivalents and Marketable Securities Financial instruments consist of cash equivalents, marketable securities, accounts receivable, net, prepaid expenses and other current assets, net, accounts payable and accrued expenses. Cash equivalents and marketable securities are stated at fair value. Prepaid expenses and other current assets, net, accounts payable and accrued expenses are stated at their carrying value, which approximates fair value due to the short time to the expected receipt or payment date. Fair value is defined as the exchange price that would be received from sale of an asset or paid to transfer a liability in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. The identification of market participant assumptions provides a basis for determining what inputs are to be used for pricing each asset or liability. A financial instrument’s classification within the fair value hierarchy is based upon the lowest level of input that is significant to the fair value measurement. A fair value hierarchy has been established which gives precedence to fair value measurements calculated using observable inputs over those using unobservable inputs. This hierarchy prioritized the inputs into three broad levels as follows: Level 1 - Quoted prices in active markets for identical assets or liabilities. Level 2 - Inputs other than Level 1 that are observable, either directly or indirectly, such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. Level 3 - Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities. The Company’s financial assets and liabilities subject to fair value measurements on a recurring basis and the level of inputs used in such measurements were as follows: June 30, 2021 Fair Value Level 1 Level 2 Level 3 (unaudited) (in thousands) Financial Assets: Money market funds $ 838,114 $ 838,114 $ — $ — Total cash equivalents $ 838,114 $ 838,114 $ — $ — U.S. government debt securities $ 853,072 $ — $ 853,072 $ — Total short-term marketable securities $ 853,072 $ — $ 853,072 $ — U.S. government debt securities $ 55,368 $ — $ 55,368 $ — Total long-term marketable securities $ 55,368 $ — $ 55,368 $ — Total $ 1,746,554 $ 838,114 $ 908,440 $ — Financial Liabilities: Contingent consideration $ 2,120 $ — $ — $ 2,120 Total $ 2,120 $ — $ — $ 2,120 December 31, 2020 Fair Value Level 1 Level 2 Level 3 (in thousands) Financial Assets: Money market funds $ 620,630 $ 620,630 $ — $ — Total cash equivalents $ 620,630 $ 620,630 $ — $ — U.S. government debt securities $ 961,902 $ — $ 961,902 $ — Total short-term marketable securities $ 961,902 $ — $ 961,902 $ — U.S. government debt securities $ 246,597 $ — $ 246,597 $ — Total long-term marketable securities $ 246,597 $ — $ 246,597 $ — Total $ 1,829,129 $ 620,630 $ 1,208,499 $ — Financial Liabilities: Contingent consideration $ 1,245 $ — $ — $ 1,245 Total $ 1,245 $ — $ — $ 1,245 The Company measures the fair value of money market funds based on quoted prices in active markets for identical securities. U.S. government debt securities are valued taking into consideration valuations obtained from third-party pricing services. The pricing services utilize industry standard valuation models, including both income and market-based approaches, for which all significant inputs are observable, either directly or indirectly, to estimate fair value. These inputs include reported trades of and broker/dealer quotes on the same or similar securities, issuer credit spreads; benchmark securities; prepayment/default projections based on historical data and other observable inputs. Acquisition-related contingent consideration is measured at fair value on a quarterly basis and change in estimated contingent consideration to be paid are included in operating expenses in the condensed consolidated statements of operations. As of June 30, 2021, and December 31, 2020, contingent consideration liability of $2.1 million and $1.2 million, respectively, was recorded within other long-term liabilities on the condensed consolidated balance sheets. The Company considers the fair value of the redeemable noncontrolling interest as of June 30, 2021, and December 31, 2020, to be a Level 3 measurement. The fair value of the redeemable noncontrolling interest was determined using a of the income approach and the market approach, and estimates and assumptions include future revenue growth rates, gross profit margins, EBITDA margins, future capital expenditures, weighted average costs of capital and future market conditions, among others. The following table summarizes the activities for the Level 3 financial instruments for the three and six months ended June 30, 2021, and 2020: Redeemable Noncontrolling Interest Contingent Consideration Three Months Ended June 30, Six Months Ended June 30, Three Months Ended June 30, Six Months Ended June 30, 2021 2020 2021 2020 2021 2020 2021 2020 (unaudited) (in thousands) Fair value — beginning of period $ 59,400 $ 45,500 $ 57,100 $ 49,600 $ 1,245 $ 1,175 $ 1,245 $ 1,365 Increase (decrease) in fair value 1,645 6,186 5,932 3,159 875 — 875 (190) Net loss for the period (1,645) (1,286) (3,632) (2,359) — — — — Fair value — end of period $ 59,400 $ 50,400 $ 59,400 $ 50,400 $ 2,120 $ 1,175 $ 2,120 $ 1,175 The Company considers the fair value of the Convertible Notes as of June 30, 2021 and December 31, 2020 to be a Level 2 measurement. The fair value of the Convertible Notes is primarily affected by the trading price of the Company's common stock and market interest rates. As such, the carrying value of the Convertible Notes does not reflect the market rate. See Note 8, Debt , for additional information related to the fair value of the Convertible Notes. Cash Equivalents and Marketable Securities The following tables summarizes the Company’s cash equivalents and marketable securities’ amortized costs, gross unrealized gains, gross unrealized losses and estimated fair values by significant investment category: June 30, 2021 Amortized Cost Gross Unrealized Gain Gross Unrealized Loss Estimated Fair Value (unaudited) (in thousands) Money market fund $ 838,114 $ — $ — $ 838,114 U.S. government debt securities 907,832 613 (5) 908,440 Total $ 1,745,946 $ 613 $ (5) $ 1,746,554 December 31, 2020 Amortized Cost Gross Unrealized Gain Gross Unrealized Loss Estimated Fair Value (in thousands) Money market fund $ 620,630 $ — $ — $ 620,630 U.S. government debt securities 1,206,195 2,339 (35) 1,208,499 Total $ 1,826,825 $ 2,339 $ (35) $ 1,829,129

Patent License Acquisition

Patent License Acquisition	6 Months Ended
	Jun. 30, 2021
Business Combinations [Abstract]
Patent License Acquisition	Patent License Acquisition In January 2017, the Company entered into a license agreement with a biotechnology company, KeyGene N.V. (“KeyGene”). An arbitration was initiated between the parties in 2018. In March 2020, the Company and KeyGene entered into a settlement and patent license agreement (the “SPLA”) to resolve the dispute and to acquire an extended worldwide non-exclusive license to certain patent rights with respect to KeyGene’s Next Generation Sequencing technologies along with certain covenant rights and research and development technology for a one-time payment of $18.5 million, ending all future royalty obligations to KeyGene. This transaction was accounted for as an asset acquisition as the purchase did not meet the definition of a business. The total consideration, including $0.6 million of certain capitalizable transaction costs, was allocated to various components of the SPLA. The Company allocated $9.4 million to the patent and covenant rights granted under the SPLA, which have useful lives in the range of 6-12 years. The Company allocated $8.5 million to IPR&D technology, which have no alternative future use and was included in research and development expenses for the six months ended June 30, 2020. The remaining $1.2 million was allocated to the settlement of the prior dispute between the parties and was included in general and administrative expenses for the six months ended June 30, 2020.

Intangible Assets, Net and Good

Intangible Assets, Net and Goodwill	6 Months Ended
	Jun. 30, 2021
Goodwill and Intangible Assets Disclosure [Abstract]
Intangible Assets, Net and Goodwill	Intangible Assets, Net and Goodwill The following table presents details of purchased intangible assets as of June 30, 2021, and December 31, 2020: June 30, 2021 Gross Carrying Amount Accumulated Amortization Net Carrying Amount Remaining Weighted Average Useful Life (unaudited) (in thousands) (in years) Intangible assets subject to amortization: Acquired license $ 11,886 $ (1,915) $ 9,971 9.3 Non-compete agreements and other covenant rights 5,100 (1,482) 3,618 4.4 Total intangible assets subject to amortization 16,986 (3,397) 13,589 Intangible assets not subject to amortization: IPR&D 1,600 — 1,600 Goodwill 3,290 — 3,290 Total purchased intangible assets $ 21,876 $ (3,397) $ 18,479 December 31, 2020 Gross Carrying Amount Accumulated Amortization Net Carrying Amount Remaining Weighted Average Useful Life (in thousands) (in years) Intangible assets subject to amortization: Acquired license $ 11,886 $ (1,367) $ 10,519 9.8 Non-compete agreements 5,100 (1,064) 4,036 4.9 Total intangible assets subject to amortization 16,986 (2,431) 14,555 Intangible assets not subject to amortization: IPR&D 1,600 — 1,600 Goodwill 3,290 — 3,290 Total purchased intangible assets $ 21,876 $ (2,431) $ 19,445 Amortization of finite-lived intangible assets was $0.5 million and $0.5 million for the three months ended June 30, 2021 and 2020, respectively, and $1.0 million and $0.8 million for the six months ended June 30, 2021, and 2020, respectively. The following table summarizes estimated future amortization expense of finite-lived intangible assets—net: Year Ending December 31, (unaudited) (in thousands) Remainder of 2021 $ 982 2022 1,947 2023 1,947 2024 1,952 2025 1,705 2026 and thereafter 5,056 Total $ 13,589

Debt

Debt	6 Months Ended
	Jun. 30, 2021
Debt Disclosure [Abstract]
Debt	Debt Convertible Senior Notes In November 2020, the Company issued $1.15 billion principal amount of its 0% Convertible Senior Notes due 2027 (the “2027 Notes”). The 2027 Notes do not bear interest, and the principal amount of the Notes will not accrete. However, special interest and additional interest may accrue on the 2027 Notes at a rate per annum not exceeding 0.50% (subject to certain exceptions) upon the occurrence of certain events such as the failure to file certain reports to the Securities and Exchange Commission, or to remove certain restrictive legends from the Notes. The Notes will mature on November 15, 2027, unless repurchased, redeemed or converted earlier. Before August 15, 2027, holders of the 2027 Notes will have the right to convert their 2027 Notes only under the following circumstances: • during any calendar quarter (and only during such calendar quarter) commencing after the calendar quarter ending on March 31, 2021, if the last reported sale price of the Company's common stock exceeds 130% of the conversion price for each of at least 20 trading days (whether or not consecutive) during the 30 consecutive trading days ending on the last trading day of the immediately preceding calendar quarter (the “sale price condition”); • during the five consecutive business days immediately after any ten consecutive trading day period (the “measurement period”) if the trading price per $1,000 principal amount of the Notes for each trading day of the measurement period is less than 98% of the product of the last reported sale price of the Company's common stock on such trading day and the conversion rate on such trading day; or • upon the occurrence of specified corporate events From and after August 15, 2027, holders of the 2027 Notes may convert their 2027 Notes at any time at their election until the close of business on the second scheduled trading day immediately before the maturity date. The Company will settle conversions by paying or delivering, as applicable, cash, shares of its common stock or a combination of cash and shares of its common stock, at the Company’s election. The initial conversion rate is 7.1523 shares of common stock per $1,000 principal amount of 2027 Notes, which represents an initial conversion price of approximately $139.82 per share of common stock. The conversion rate and conversion price will be subject to customary adjustments upon the occurrence of certain events. In addition, if certain corporate events that constitute a “Make-Whole Fundamental Change” occur, then the conversion rate will, in certain circumstances, be increased for a specified period of time. The Company may not redeem the 2027 Notes at its option at any time before November 20, 2024. The Notes will be redeemable, in whole or in part, at the Company’s option at any time, and from time to time, on or after November 20, 2024 and on or before the 25th scheduled trading day immediately before the maturity date, at a cash redemption price equal to the principal amount of the Notes to be redeemed, plus accrued and unpaid special interest and additional interest, if any, to, but excluding, the redemption date, but only if the last reported sale price per share of the Company’s common stock exceeds 130% of the conversion price on (i) each of at least 20 trading days, whether or not consecutive, during the 30 consecutive trading days ending on, and including, the trading day immediately before the date the Company sends the related redemption notice; and (ii) the trading day immediately before the date the Company sends such notice. In addition, calling any Note for redemption will constitute a Make-Whole Fundamental Change with respect to that Note, in which case the conversion rate applicable to the conversion of that Note will be increased in certain circumstances if it is converted after it is called for redemption. If certain corporate events that constitute a “Fundamental Change” occur, then, subject to a limited exception for certain cash mergers, holders of Notes may require the Company to repurchase their 2027 Notes at a cash repurchase price equal to the principal amount of the 2027 Notes to be repurchased, plus accrued and unpaid special interest and additional interest, if any, to, but excluding, the fundamental change repurchase date. The definition of Fundamental Change includes certain business combination transactions involving the Company and certain de-listing events with respect to the Company’s common stock. In accounting for the 2027 Notes, the Company separated the 2027 Notes into liability and equity components. The carrying amount of the liability component was calculated using a Black-Scholes model by measuring the fair value of a similar instrument that does not have an associated convertible feature. The carrying amount of the equity component representing the conversion option was determined by deducting the fair value of the liability component from the par value of the 2027 Notes as a whole. This difference represents a debt discount that is amortized as interest expense using an effective interest over the term of the 2027 Notes. Effective January 1, 2021, the Company early adopted ASU 2020-06 which resulted in the re-classification of the equity component representing the associated convertible feature and the related debt issuance costs into long-term liabilities with a corresponding impact to retained earnings. Since the 2027 Notes were not convertible as of June 30, 2021, the net carrying amount of the 2027 Notes was classified as a long-term liability. The following table sets forth the components of the 2027 Notes as of June 30, 2021, and December 31, 2020: June 30, 2021 December 31, 2020 (unaudited) (in thousands) Liability component: Principal $ 1,150,000 $ 1,150,000 Less: debt discount, net of amortization — (331,074) Less: debt issuance costs, net of amortization (16,461) (12,634) Net carrying amount $ 1,133,539 $ 806,292 Equity component recorded at issuance: 2027 Notes $ — $ 335,667 Less: issuance costs — (5,264) Net amount recorded in equity $ — $ 330,403 The total estimated fair value of the 2027 Notes was $1.3 billion and $1.3 billion as of June 30, 2021, and December 31, 2020, respectively. The fair value was determined based on the closing trading price per $100 of the 2027 Notes as of the last day of trading for the period. The interest expense recognized in relation to amortization of debt issuance costs was $0.6 million and $1.3 million for the three and six months ended June 2021, which represented an effective interest rate of 0.2% and 0.2% and for the three and six months ended June 2021. Note Hedges To minimize the impact of potential economic dilution upon conversion of the 2027 Notes, the Company entered into convertible note hedge transactions (the "2027 Note Hedges") with respect to its common stock concurrent with the issuance of the Notes. The 2027 Note Hedges cover, subject to customary adjustments, the number of shares of common stock initially underlying the Notes. The strike price of the 2027 Note Hedges will initially be approximately $182.60 per share, which represents a premium of 75% over the last reported sale price of the Company’s common stock of $104.34 per share on November 16, 2020, and is subject to certain adjustments under the terms of the 2027 Note Hedges. The 2027 Note Hedges will expire upon maturity of the 2027 Notes. The 2027 Note Hedges are separate transactions and are not part of the terms of the 2027 Notes. Holders of the 2027 Notes will not have any rights with respect to the 2027 Note Hedges. The shares receivable related to the 2027 Note Hedges are excluded from the calculation of diluted earnings per share as they are anti-dilutive.

Leases

Leases	6 Months Ended
	Jun. 30, 2021
Leases [Abstract]
Leases	Leases The Company has entered into various operating lease agreements for office space, data center, lab and warehouse use, with remaining terms ranging from 1 year to 12 years some of which include one or more options to renew. As leases approach maturity, the Company considers various factors such as market conditions and the terms of any renewal options that may exist to determine whether it will renew the lease, as such, the Company does not include renewal options in its lease terms for calculating its lease liability, as the renewal options allow it to maintain operational flexibility and the Company is not reasonably certain it will exercise these renewal options at the time of the lease commencement. In July 2020, the Company entered into two lease agreements for additional office space in Palo Alto, California ("Palo Alto Lease") and in San Diego, California ("San Diego Lease"). The San Diego Lease has a term of 8 years with rent payments commencing in May 2022. The Palo Alto Lease has a term of 12 years with an option to renew the lease term for an additional ten years which has not been considered in the determination of ROU or the lease liability as the Company does not consider it reasonably certain of exercising the renewal option. Rent payments for the Palo Alto Lease will commence in October 2021. Both leases consist of fixed and variable payments and are being accounting for as operating leases. The Company took possession of these facilities in March 2021. The Company estimated the incremental borrowing rate to determine the present value of lease payments for the San Diego and Palo Alto leases using trading data of the Company's convertible debt adjusted for credit rating and market yield curves. Operating lease expense was $6.9 million and $1.9 million for the three months ended June 30, 2021, and 2020, respectively, and $10.8 million and $3.4 million for the six months ended June 30, 2021, and 2020, respectively, which includes both lease and non-lease components (primarily common area maintenance charges and property taxes). June 30, 2021 December 31, 2020 (unaudited) Weighted-average remaining lease term (in years) 10.3 5.5 Weighted-average discount rate 4.14 % 8.07 % The following table summarizes the Company's future principal contractual obligations for operating lease commitments as of June 30, 2021: Year Ending December 31, (unaudited) (in thousands) Remainder of 2021 $ 5,398 2022 21,454 2023 28,976 2024 31,529 2025 32,084 2026 and thereafter 177,402 Total operating lease payments $ 296,843 Less: imputed interest (54,792) Less: lease incentives (22,721) Total operating lease liabilities $ 219,330 Finance leases are not material to the Company's condensed consolidated financial statements.

Commitments and Contingencies

Commitments and Contingencies	6 Months Ended
	Jun. 30, 2021
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Legal Proceedings In addition to commitments and obligations incurred in the ordinary course of business, from time to time the Company may be subject to a variety of claims and legal proceedings, including claims from customers and vendors, pending and potential legal actions for damages, governmental investigations and other matters. For example, the Company has received, and may in the future continue to receive letters, claims or complaints from others alleging false advertising, patent infringement, violation of employment practices and trademark infringement. The Company has also instituted, and may in the future institute, additional legal proceedings to enforce its rights and seek remedies, such as monetary damages, injunctive relief and declaratory relief. The Company cannot predict the results of any such disputes, and despite the potential outcomes, the existence thereof may have an adverse material impact on the Company because of diversion of management time and attention as well as the financial costs related to resolving such disputes. The Company and its affiliates are parties to the legal claims and proceedings described below. The Company is vigorously defending itself against those claims and in those proceedings. Significant developments in those matters are described below. If the Company is unsuccessful in defending, or if it determines to settle, any of these matters, it may be required to pay substantial sums, be subject to injunction and/or be forced to change how it operates its business, which could have a material adverse impact on its financial position or results of operations. Unless otherwise stated, the Company is unable to reasonably estimate the loss or a range of possible loss for the matters described below. Often, it is not reasonably possible for the Company to determine that a loss is probable for a claim, or to reasonably estimate the amount of loss or a range of loss, because of the limited information available and the potential effects of future events and decisions by third parties, such as courts and regulators, that will determine the ultimate resolution of the claim. Many of the matters described are at preliminary stages, raise novel theories of liability or seek an indeterminate amount of damages. It is not uncommon for claims to be resolved over a number of years. The Company reviews loss contingencies at least quarterly to determine whether the loss probability has changed and whether it can make a reasonable estimate of the possible loss or range of loss. When the Company determines that a loss from a claim is probable and reasonably estimable, it records a liability in the amount of its estimate for the ultimate loss. The Company also provides disclosure when it is reasonably possible that a loss may be incurred or when it is reasonably possible that the amount of a loss will exceed its recorded liability. Patent Disputes In November 2017, the Company filed a lawsuit against Foundation Medicine, Inc. (“Foundation Medicine”) in the United States District Court for the District of Delaware. The Company has alleged that Foundation Medicine has infringed four of the Company’s digital sequencing technology patents. Foundation Medicine has asserted counterclaims of patent invalidity, unenforceability under the doctrine of inequitable conduct, license and noninfringement. The parties are seeking damages, injunctive relief and attorneys’ fees. Discovery in the lawsuit has closed, and a number of pre-trial motions were filed in September and October 2020. Foundation Medicine also filed six petitions for inter partes review with the PTAB, challenging the patentability of all four of the patents asserted by the Company. The PTAB denied institution of inter partes review for four of the six petitions filed by Foundation Medicine and instituted inter partes review for the remaining two petitions. In November 2020, the Company filed a lawsuit against Foundation Medicine in the United States District Court for the District of Delaware, wherein the Company alleged that Foundation Medicine infringes seven of the Company’s patents. Foundation Medicine has asserted counterclaims of patent invalidity, unenforceability under the doctrine of inequitable conduct, license, non-infringement, and that the Company has violated Section 2 of Sherman Act. In December 2020, the Company filed a Motion for a Preliminary Injunction to prohibit Foundation Medicine from practicing two of the asserted patents. In March 2021, the Company filed two lawsuits against Foundation Medicine GmbH in the District Court of Munich I in Germany, wherein the Company alleged that Foundation Medicine GmbH infringes two of the Company’s patents. Final hearings on this matter are scheduled for December 2021. In May 2021, the Company entered into a binding term sheet with Foundation Medicine, which upon execution of a definitive settlement agreement, will result in the dismissal of all pending patent litigation worldwide between the parties. In August 2020, the Company and Personal Genome Diagnostics, Inc. settled the patent infringement lawsuit brought by the Company. Under the terms of the confidential settlement, the lawsuit and counterclaims, as well as other challenges to the Company’s patents, have been dismissed. In August 2021, TwinStrand Biosciences, Inc. and the University of Washington filed a patent infringement suit in the United States District Court for the District of Delaware alleging that the Company infringes U.S. Patent Nos. 10,287,631; 10,689,699; 10,752,951; and 10,760,127. The Company will respond to the complaint and present its defenses to the allegations. False Advertising Dispute

Common Stock

Common Stock	6 Months Ended
	Jun. 30, 2021
Equity [Abstract]
Common Stock	Common StockThe Company’s common stockholders are entitled to dividends if and when declared by the Company’s Board of Directors (the “Board of Directors”). As of June 30, 2021 and December 31, 2020, no dividends on the Company's common stock had been declared by the Board of Directors. The Company’s common stock has been reserved for the following potential future issuances: June 30, 2021 December 31, 2020 (unaudited) Shares underlying outstanding stock options 2,703,906 3,101,181 Shares underlying unvested restricted stock units 1,155,370 1,118,655 Market-based restricted stock units 2,260,764 3,391,148 Performance-based restricted stock units 415,535 377,922 Shares available for issuance under the 2018 Incentive Award Plan 5,928,052 1,819,223 Shares available for issuance under the 2018 Employee Stock Purchase Plan 1,475,593 1,536,491 Total 13,939,220 11,344,620 Follow-on Public Offering In June 2020, the Company completed an underwritten public offering, in which it issued and sold 4,312,500 shares of its common stock at a price of $84.00 per share. The Company received net proceeds of $354.6 million after deducting underwriting discounts and commissions and offering expenses payable by the Company.

Stock-Based Compensation

Stock-Based Compensation	6 Months Ended
	Jun. 30, 2021
Share-based Payment Arrangement [Abstract]
Stock-Based Compensation	Stock-Based Compensation Stock Option Activity A summary of the Company’s stock option activity under the 2012 Stock Plan (as amended and restated, the “2012 Plan”) and the 2018 Incentive Award Plan (the “2018 Plan”) and related information is as follows: Options Outstanding Shares Shares Subject to Options Outstanding Weighted-Average Exercise Price Weighted-Average Remaining Contractual Life (Years) Aggregate Intrinsic Value (unaudited) (in thousands) Balance as of December 31, 2020 1,819,223 3,101,181 $ 15.80 6.9 $ 350,670 2018 Plan annual increase (1) 3,689,000 — Granted (60,677) 60,677 142.73 Exercised — (371,711) 14.34 Canceled 42,956 (86,241) 47.02 Restricted stock units granted (177,166) — — Restricted stock units canceled 94,075 — — Market-based restricted stock units canceled 558,254 — — Performance-based restricted stock units granted (52,917) — — Performance-based restricted stock units canceled 15,304 — — Balance as of June 30, 2021 5,928,052 2,703,906 $ 17.86 6.5 $ 288,749 Vested and Exercisable as of June 30, 2021 2,091,339 $ 9.16 6.1 $ 240,569 (1) Effective as of January 1, 2021, an additional 3,689,000 shares of common stock became available for issuance under the 2018 Plan, as a result of the operation of an automatic annual increase provision therein. Aggregate intrinsic value represents the difference between the estimated fair value of the underlying common stock and the exercise price of outstanding, in-the-money options. The total intrinsic value of the options exercised was $11.1 million and $33.1 million for the three months ended June 30, 2021 and 2020, respectively, and $49.4 million and $50.3 million for the six months ended June 30, 2021 and 2020, respectively. The weighted-average grant date fair value of options granted was $81.79 and $44.61 per share for the three months ended June 30, 2021 and 2020, respectively, and $84.02 and $45.52 per share for the six months ended June 30, 2021 and 2020, respectively. Future stock-based compensation for unvested options as of June 30, 2021 was $19.7 million, which is expected to be recognized over a weighted-average period of 2.7 years. Restricted Stock Units A summary of the Company’s restricted stock unit activity excluding the performance-based and market-based restricted stock units under the 2012 Plan and the 2018 Plan and related information is as follows: Restricted Stock Units Outstanding Weighted-Average Grant Date Fair Value (unaudited) Balance as of December 31, 2020 1,118,655 $ 92.89 Granted 177,166 154.94 Vested and released (46,376) 80.32 Canceled (94,075) 92.67 Balance as of June 30, 2021 1,155,370 $ 102.93 Future stock-based compensation for unvested restricted stock units as of June 30, 2021, was $98.1 million, which is expected to be recognized over a weighted-average period of 3.1 years. Performance-based Restricted Stock Units Since November 2020, the Compensation Committee of the Board of Directors started to approve, and the Company started to grant performance-based restricted stock units (“PSUs”) under the 2018 Plan. The PSUs granted to employees consist of financial and operational metrics to be met over a performance period of 4 years and an additional service period requirement of six months after the performance metrics are met. The PSUs granted to a consultant consistent of operational metrics to be met over a performance period of 4 years. The PSUs are expected to be expensed over a period of approximately 4 years to 4.5 years subject to meeting the respective performance metrics and service requirements. As of June 30, 2021, a significant portion of these PSUs are not expected to achieve the related performance metrics, and therefore, no stock-based compensation expense was recorded for the PSUs that were not probable to vest. A summary of the Company’s performance-based restricted stock unit activity under the 2018 Plan and related information is as follows: Performance-based Restricted Stock Units Outstanding Weighted-Average Grant Date Fair Value (unaudited) Balance as of December 31, 2020 377,922 $ 113.40 Granted 52,917 135.94 Canceled (15,304) 113.40 Balance as of June 30, 2021 415,535 $ 116.27 Stock-based compensation recorded for the PSUs for the three and six months ended June 30, 2021 was $0.3 million and $0.7 million, respectively. Future stock-based compensation for unvested PSUs that are probable to vest as of June 30, 2021 was $4.9 million, which is expected to be recognized over a weighted-average period of 3.6 years. Market-based Restricted Stock Units In May 2020, the Board of Directors approved and granted 1,695,574 market-based restricted stock units (“MSUs”) under the 2018 Plan to each of the Company's Chief Executive Officer and the Company's President and Chief Operating Officer, which is subject to the achievement of market-based share price goals established by the Board of Directors. The MSUs consist of three separate tranches and the vesting of each tranche is subject to the Company's common stock closing price being maintained at or above a predetermined share price goal for a period of 30 consecutive calendar days. The share price goal can be met any time during the seven-year performance period from the date of grant. Upon vesting, the MSUs must be held for a period of six Tranche Price Goal Number of RSUs Tranche 1 $120 per share 565,192 Tranche 2 $150 per share 565,191 Tranche 3 $200 per share 565,191 The grant date fair values of the MSUs were determined using a Monte Carlo valuation model for each tranche. The related stock-based compensation expense for each tranche is recognized based on an accelerated attribution method over the estimated derived service period. If the related share price goal is achieved earlier than its expected derived service period, the stock-based compensation expense will be recognized as a cumulative catch-up expense from the grant date to that point in time in achieving the share price goal. The derived service period is the median duration of the successful stock price paths to meet the price goal for each tranche as simulated in the Monte Carlo valuation model. The Monte Carlo valuation model uses assumptions such as volatility, risk-free interest rate, cost of equity and dividend estimated for the performance period of the MSU. The weighted average grant date fair value of the MSUs was $67.00 and the weighted average derived service period was estimated to be in the range of 0.83 – 2.07 years. On January 1, 2021, Tranche 1 of the MSUs became vested because it has met both service requirement and market-based performance metrics as the predetermined share price goal of $120 per share was achieved for a period of 30 consecutive calendar days. A summary of the Company’s market-based restricted stock unit activity under the 2018 Plan and related information is as follows: Market-based Restricted Stock Units Outstanding Weighted-Average Grant Date Fair Value (unaudited) Balance as of December 31, 2020 3,391,148 $ 67.00 Vested and released (572,130) 70.58 Canceled (1) (558,254) 70.58 Balance as of June 30, 2021 2,260,764 $ 65.20 (1) Represented shares withheld by the Company for MSU holders' tax obligation upon release of vested MSUs. For the three and six months ended June 30, 2021, stock-based compensation for the MSUs was $22.3 million and $66.3 million, respectively, which was recorded in general and administrative expenses on the condensed consolidated statement of operations. Future stock-based compensation for unvested MSUs as of June 30, 2021 was $49.0 million, which is expected to be recognized over a weighted-average period of 0.8 years. In the event of a change in control, a qualifying termination, death, disability or the share price goal occurring earlier than the estimated derived service period, the stock-based compensation relating to these MSUs could be accelerated. Any MSUs that remain unvested at the end of the seven-year performance period will automatically be forfeited and terminated without further consideration. AMEA 2020 Equity Incentive Plan In August 2020, the board of directors of the Joint Venture approved its 2020 Equity Incentive Plan (the “AMEA 2020 Plan”), under which the Joint Venture may grant equity incentive awards such as stock options, restricted stock, restricted stock units, stock appreciation rights and cash-based awards to its employees and non-employees. Stock options granted may be either incentive stock options or nonstatutory stock options. Incentive stock options may be granted only to employees of the Joint Venture or its affiliates. Nonstatutory stock options may be granted to employees, directors and non-employee consultants. Stock options may be granted at an exercise price of not less than the fair market value of the Joint Venture's common stock on the date of grant, determined by the board of directors of the Joint Venture. Options generally vest over 4 years and expire as determined by the board of directors of the Joint Venture, provided that the term of options may not exceed 10 years from the date of grant. For individuals holding more than 10% of the total combined voting power of all classes of stock of the Joint Venture, the exercise price of an option will not be less than 110% of the fair market value of the Joint Venture's common stock on the date of grant, and the term of the option will not exceed 5 years. A total of 4,595,555 shares of the Joint Venture's Class B common stock are initially reserved for issuance under the AMEA 2020 Plan, and the number of shares may be increased in accordance with the terms of the AMEA 2020 Plan. A summary of the Joint Venture's stock option activity under the AMEA 2020 Plan and related information is as follows: Options Outstanding Shares Shares Subject to Options Outstanding Weighted-Average Exercise Price Weighted-Average Remaining Contractual Life (Years) Aggregate Intrinsic Value (unaudited) (in thousands) Balance as of December 31, 2020 542,220 4,053,335 $ 0.58 9.6 $ — Granted (382,223) 382,223 0.58 Exercised — (91,109) 0.58 Canceled 92,412 (92,412) 0.58 Balance as of June 30, 2021 252,409 4,252,037 $ 0.58 9.2 $ — Vested and Exercisable as of June 30, 2021 2,352,180 $ 0.58 9.1 $ — The weighted-average grant date fair value of options granted was $0.33 per share for the three and six months ended June 30, 2021. Future stock-based compensation for unvested options as of June 30, 2021 was $0.6 million, which is expected to be recognized over a weighted-average period of 2.2 years. Stock-Based Compensation Expense The following table presents the effect of employee and non-employee related stock-based compensation expense including the Joint Venture: Three Months Ended Six Months Ended 2021 2020 2021 2020 (unaudited) (in thousands) Cost of precision oncology testing $ 873 $ 407 $ 1,640 $ 710 Research and development expense 4,564 2,622 8,864 4,986 Sales and marketing expense 3,438 2,167 6,318 3,965 General and administrative expense 25,632 20,619 72,754 22,492 Total stock-based compensation expense $ 34,507 $ 25,815 $ 89,576 $ 32,153 Valuation of Stock Options The grant date fair value of stock options was estimated using a Black-Scholes option-pricing model with the following weighted-average assumptions including the Joint Venture: Three Months Ended Six Months Ended 2021 2020 2021 2020 (unaudited) Expected term (in years) 5.49 – 6.04 5.50 – 6.10 5.49 – 6.04 5.50 – 6.10 Expected volatility 63.6% – 66.7% 66.5% – 68.5% 63.6% – 66.7% 66.5% – 73.3% Risk-free interest rate 0.3% – 1.1% 0.4% – 0.4% 0.3% – 1.1% 0.4% – 1.6% Expected dividend yield —% —% —% —% The determination of the fair value of stock options on the date of grant using a Black-Scholes option-pricing model is affected by the estimated fair value of common stock of the Company and the Joint Venture, as well as assumptions regarding a number of variables that are complex, subjective and generally require significant judgment to determine. The valuation assumptions were determined as follows : Fair Value of Common Stock The fair value of the Company’s common stock is determined by the closing price, on the date of grant, of its common stock, which is traded on the Nasdaq Global Select Market. The grant date fair value of the Joint Venture's common stock has been determined by the board of directors of the Joint Venture. The grant date fair value of the Joint Venture’s common stock was determined using valuation methodologies which utilize certain assumptions including probability weighting of events, volatility, time to liquidation, a risk-free interest rate and an assumption for a discount for lack of marketability. In determining the fair value of the Joint Venture’s common stock, the methodologies used to estimate the enterprise value of the Joint Venture were performed using methodologies, approaches, and assumptions consistent with the American Institute of Certified Public Accountants Accounting and Valuation Guide, Valuation of Privately-Held-Company Equity Securities Issued as Compensation . Expected Term The expected term represents the period that the options granted are expected to be outstanding and is determined using the simplified method (based on the mid-point between the vesting date and the end of the contractual term) as the Company has concluded that its stock option exercise history does not provide a reasonable basis upon which to estimate expected term. Expected Volatility Prior to the commencement of trading of the Company’s common stock on the Nasdaq Global Select Market on October 4, 2018 in connection with the IPO, there was no active trading market for the Company's common stock. Due to limited historical data for the trading of the Company’s common stock, expected volatility is estimated based on the average volatility for comparable publicly traded peer group companies in the same industry plus the Company's expected volatility for the available periods. The comparable companies are chosen based on their similar size, stage in the life cycle or area of specialty. The Joint Venture derived the expected volatility from the average historical volatility over a period approximately equal to the expected term of comparable publicly traded companies within its peer group that were deemed to be representative of future stock price trends as the Joint Venture does not have any trading history for its common stock. The Joint Venture will continue to apply this process until a sufficient amount of historical information regarding the volatility of its own stock price becomes available. Risk-Free Interest Rate The risk-free interest rate is based on the U.S. Treasury rate, with maturities similar to the expected term of the stock options. Expected Dividend Yield The Company and the Joint Venture does not anticipate paying any dividends in the foreseeable future and, therefore, uses an expected dividend yield of zero. Valuation of MSUs The estimated fair value of the MSUs was determined using a Monte Carlo simulation model. The valuation assumptions used were substantially consistent with the assumption used to value stock options with the exception of the following: Expected Volatility Due to limited historical data for the trading of the Company’s common stock, expected volatility is estimated based on the average volatility for comparable publicly traded peer group companies and implied volatility of publicly traded options in the same industry plus the Company's expected volatility for the available periods. The comparable companies are chosen based on their similar size, stage in the life cycle or area of specialty. Expected Term The expected term represents the derived service period for the respective tranches which has been estimated using the Monte Carlo simulation model. Risky Rate The risky rate represents the Company's cost of equity. Discount for Lack of Marketability The discount for lack of marketability represents the discount applied for post vest term restrictions and has been derived using the Monte Carlo simulation model. The following assumptions were used to calculate the stock-based compensation for MSUs: a weighted-average expected term of 0.83 – 2.07 years; expected volatility of 65.5%; a risk-free interest rate of 0.53%; a zero dividend yield; a risky rate (cost of equity) of 16%; and a discount for post-vesting restrictions of 10.4% – 14.5%. 2018 Employee Stock Purchase Plan In September 2018, the Company’s Board of Directors adopted and its stockholders approved the 2018 Employee Stock Purchase Plan (the “ESPP”). A total of 922,250 shares of common stock were initially reserved for issuance under the ESPP. Effective as of January 1, 2020, an additional 942,614 shares of common stock became available for issuance under the ESPP, as a result of the operation of an automatic annual increase provision therein. Subject to any plan limitations, the ESPP allows eligible employees to contribute, normally through payroll deductions, up to 10% of their earnings for the purchase of the Company’s common stock at a discounted price per share. The price at which common stock is purchased under the ESPP is equal to 85% of the fair market value of the Company’s common stock on the first or last day of the offering period, whichever is lower. The ESPP provides for separate six-month offering periods beginning on May 15 and November 15 of each year. Shares of common stock purchased under the ESPP were 60,898 and 58,164 for the three and six months ended June 30, 2021 and 2020, respectively. The total compensation expense related to the ESPP was $0.8 million and $1.1 million for the three months ended June 30, 2021 and 2020, respectively, and $1.6 million and $1.6 million for the six months ended June 30, 2021 and 2020, respectively. The fair value of the stock purchase right granted under the ESPP was estimated on the first day of each offering period using the Black-Scholes option pricing model. The valuation assumptions used were substantially consistent with the assumption used to value stock options with the exception of the expected term which was based on the term of each purchase period. The grant date fair value of the stock purchase right granted under the ESPP was estimated using a Black-Scholes option-pricing model with the following weighted-average assumptions: Three and Six Months Ended June 30, 2021 2020 (unaudited) Expected term (in years) 0.5 0.5 Expected volatility 50.8% 73.2% Risk-free interest rate —% 0.2% Expected dividend yield —% —% As of June 30, 2021, the unrecognized stock-based compensation expense related to the ESPP was $1.4 million, which is expected to be recognized over the remaining term of the offering period of 0.4 years.

Net Loss Per Share Attributable

Net Loss Per Share Attributable to Guardant Health, Inc. Common Stockholders	6 Months Ended
	Jun. 30, 2021
Earnings Per Share [Abstract]
Net Loss Per Share Attributable to Guardant Health, Inc. Common Stockholders	Net Loss Per Share Attributable to Guardant Health, Inc. Common Stockholders The following table sets forth the computation of the basic and diluted net loss per share attributable to Guardant Health, Inc. common stockholders: Three Months Ended Six Months Ended 2021 2020 2021 2020 (unaudited) (in thousands, except per share data) Net loss $ (97,575) $ (49,739) $ (204,933) $ (81,568) Adjustment of redeemable noncontrolling interest — (4,900) (2,300) (800) Net loss attributable to Guardant Health, Inc. common stockholders, basic and diluted $ (97,575) $ (54,639) $ (207,233) $ (82,368) Net loss per share attributable to Guardant Health, Inc. common stockholders, basic and diluted $ (0.96) $ (0.57) $ (2.05) $ (0.87) Weighted-average shares used in computing net loss per share attributable to Guardant Health, Inc. common stockholders, basic and diluted 101,172 96,011 101,064 95,196 Since the Company was in a loss position for all periods presented, basic net loss per share attributable to Guardant Health, Inc. common stockholders is the same as diluted net loss per share attributable to Guardant Health, Inc. common stockholders, as the inclusion of all potential shares of common stock outstanding would have been anti-dilutive. The following weighted-average common stock equivalents were excluded from the calculation of diluted net loss per share attributable to Guardant Health, Inc. common stockholders for the periods presented as they had an anti-dilutive effect: Three Months Ended Six Months Ended 2021 2020 2021 2020 (unaudited) (in thousands) Stock options issued and outstanding (1) 2,720 4,056 2,816 4,200 Restricted stock units 1,147 542 1,133 519 MSUs 2,261 1,342 2,453 671 PSUs 409 — 408 — ESPP obligation 43 37 45 40 Common stock subject to repurchase 8 20 10 21 Convertible senior notes 8,225 — 8,225 — Total 14,813 5,997 15,090 5,451

Income Taxes

Income Taxes	6 Months Ended
	Jun. 30, 2021
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The income tax expense for the three and six months ended June 30, 2021 was determined based upon estimates of the Company’s effective income tax rates in various jurisdictions. The difference between the Company’s effective income tax rate and the U.S. federal statutory rate is primarily attributable to state income taxes, foreign income taxes, the effect of certain permanent differences, and full valuation allowance against net deferred tax assets. The income tax expense for the three and six months ended June 30, 2021 and 2020 relates primarily to state minimum income tax and income tax on the Company’s earnings in foreign jurisdictions.

Segment and Geographic Informat

Segment and Geographic Information	6 Months Ended
	Jun. 30, 2021
Segment Reporting [Abstract]
Segment and Geographic Information	Segment and Geographic Information The following table sets forth the Company’s revenue by geographic areas based on the customers’ locations: Three Months Ended Six Months Ended 2021 2020 2021 2020 (unaudited) (in thousands) United States $ 87,868 $ 61,422 $ 160,168 $ 126,035 International (1) 4,233 4,913 10,598 7,810 Total revenue $ 92,101 $ 66,335 $ 170,766 $ 133,845 (1) No single country outside of the United States accounted for more than 10% of total revenue during the three and six months ended June 30, 2021 and 2020, respectively. As of June 30, 2021 and December 31, 2020, 98% and 94%, respectively, of the Company’s long-lived assets and right-of-use assets are located in the United States.

Related Party Transactions

Related Party Transactions	6 Months Ended
	Jun. 30, 2021
Related Party Transactions [Abstract]
Related Party Transactions	Related Party Transactions As discussed in Note 3, Investment in Joint Venture , the Company and an affiliate of SoftBank formed and capitalized the Joint Venture to accelerate commercialization of its products in Asia, the Middle East and Africa. The Company has consolidated the financial position, results of operations and cash flows of the Joint Venture in its financial statements and all intercompany balances have been eliminated in consolidation. The Company and its subsidiaries may, in the ordinary course of business, have transactions with unaffiliated companies of which certain of the Company’s directors are directors and/or executive officers. The Company believes that such transactions are on the same terms generally offered by such other companies to other entities in comparable transactions. The Company does not consider the amounts involved in such transactions to be material in relation to its businesses, the businesses of such other companies or the interests of the directors involved.

Subsequent Events

Subsequent Events	6 Months Ended
	Jun. 30, 2021
Subsequent Events [Abstract]
Subsequent Events	Subsequent EventsPursuant to a shares subscription agreement entered into in June 2021, the Company acquired $26 million of non-marketable securities in July 2021.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	6 Months Ended
	Jun. 30, 2021
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The Company’s condensed consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”). The accompanying condensed consolidated financial statements include the accounts of Guardant Health, Inc., its consolidated Joint Venture and majority owned subsidiary. Other stockholders’ interests in the Joint Venture are shown in the condensed consolidated financial statements as redeemable noncontrolling interest. All significant intercompany balances and transactions have been eliminated in consolidation. The Company believes that its existing cash and cash equivalents and marketable securities as of June 30, 2021, will be sufficient to allow the Company to fund its current operating plan through at least a period of one year after the date the accompanying condensed consolidated financial statements are issued. As the Company continues to incur losses, its transition to profitability is dependent upon a level of revenues adequate to support the Company’s cost structure. If the Company’s transition to profitability is not consistent with its current operating plan, the Company may have to seek additional capital.
Use of Estimates	Use of Estimates The preparation of condensed consolidated financial statements in conformity with GAAP requires management to make certain estimates, judgments and assumptions that affect the reported amounts of assets and liabilities and the related disclosures at the date of the condensed consolidated financial statements, as well as the reported amounts of revenues and expenses during the periods presented. The Company bases its estimates on historical experience and other market-specific or other relevant assumptions that it believes to be reasonable under the circumstances. Estimates are used in several areas including, but not limited to, estimation of variable consideration, estimation of credit losses, standalone selling price allocation included in contracts with multiple performance obligations, goodwill and identifiable intangible assets, stock-based compensation, incremental borrowing rate for operating leases, contingencies, certain inputs into the provision for income taxes, including related reserves, valuation of non-
Unaudited Interim Condensed Financial Statements	Unaudited Interim Condensed Financial Statements The accompanying condensed consolidated balance sheet as of June 30, 2021, the condensed consolidated statements of operations for the three and six months ended June 30, 2021, and 2020, the condensed consolidated statements of comprehensive loss for the three and six months ended June 30, 2021, and 2020, the condensed consolidated statements of redeemable noncontrolling interest and stockholders’ equity for the three and six months ended June 30, 2021, and 2020, and cash flows for the six months ended June 30, 2021, and 2020, and the related interim condensed consolidated disclosures are unaudited. The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with GAAP for interim financial information and in accordance with the instructions to Form 10-Q and Rule 10-01 of Regulation S-X of the Securities Act of 1933, as amended (the “Securities Act”). Accordingly, they do not include all of the information and notes required by GAAP for complete financial statements. These unaudited condensed consolidated financial statements include all adjustments, consisting only of normal recurring accruals that the Company believes are necessary to fairly state the financial position and the results of the Company’s operations and cash flows for interim periods in accordance with GAAP. Interim-period results are not necessarily indicative of results of operations or cash flows for a full year or any subsequent interim period. The accompanying condensed consolidated financial statements should be read in conjunction with the Company’s audited financial statements and notes thereto included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2020.
Foreign Currency	Foreign Currency The functional currency of the subsidiaries of the consolidated Joint Venture is the local currency. The assets and liabilities of the subsidiaries are translated into U.S. dollars at exchange rates in effect at each balance sheet date, with the resulting translation adjustments recorded to a separate component of accumulated other comprehensive loss within stockholders’ equity. Income and expense accounts are translated at average exchange rates during the period. Foreign currency transaction gains and losses resulting from transactions denominated in a currency other than the functional currency are recognized in the condensed consolidated statements of operations. For the three and six months ended June 30, 2021, and 2020, foreign currency transaction gains and losses were immaterial.
Concentration of Risk	Concentration of Risk The Company is subject to credit risk from its portfolio of cash equivalents held at one commercial bank and investments in marketable securities. The Company limits its exposure to credit losses by investing in money market funds through a U.S. bank with high credit ratings. The Company’s cash may consist of deposits held with banks that may at times exceed federally insured limits, however, its exposure to credit risk in the event of default by the financial institution is limited to the extent of amounts recorded on the condensed consolidated balance sheets. The Company performs evaluations of the relative credit standing of these financial institutions to limit the amount of credit exposure. The Company also invests in investment-grade debt instruments and has policy limits for the amount it can invest in any one type of security, except for securities issued or guaranteed by the U.S. government. The goals of the Company’s investment policy, in order of priority, are as follows: safety and preservation of principal and diversification of risk; liquidity of investments sufficient to meet cash flow requirements; and a competitive after-tax rate of return. Under its investment policy, the Company limits amounts invested in such securities by credit rating, maturity, investment type and issuer, as a result, the Company is not exposed to any significant concentrations of credit risk from these financial instruments. The Company is subject to credit risk from its accounts receivable. The majority of the Company’s accounts receivable arises from the provision of precision oncology services and development services and other in the United States and are primarily with biopharmaceutical companies with high credit ratings. The Company has not experienced any material losses related to receivables from individual customers, or groups of customers. The Company does not require collateral. Accounts receivable are recorded at net amount.
Accounts Receivable, Net	Accounts Receivable, Net Accounts receivable represent valid claims against biopharmaceutical companies, research institutes and international distributors. The Company evaluates the collectability of its accounts receivable based on historical collection trends, the financial condition of payment partners, and external market factors and provides for an allowance for potential credit losses based on management’s best estimate of the amount of probable credit losses. As of June 30, 2021, and December 31, 2020, the Company had immaterial allowance for credit losses related to its accounts receivable. Contract assets are presented under accounts receivable, net and other assets, net on the Company’s condensed consolidated balance sheets and include balances from commercial and governmental payers. Contract assets consists primarily of: i) precision oncology testing revenues to clinical customers that are recognized upon delivery of the test results prior to cash collection; and ii) development services and other revenues to biopharmaceutical customers that are recognized upon the achievement of performance-based milestones but prior to the establishment of billing rights. Contract assets are relieved when the Company receives payments from clinical customers, or when it invoices the biopharmaceutical customers when milestones are achieved, thereby reclassifying the balances from contract assets to accounts receivable. As of June 30, 2021, the Company had contract assets of $24.8 million which was recorded in accounts receivable, net. As of December 31, 2020, the Company had contract assets of $15.6 million which was recorded in accounts receivable, net, which included $8.4 million of unbilled receivable relating to Guardant360 CDx.
Asset Acquisition	Asset Acquisition If an acquisition of an asset or group of assets does not meet the definition of a business, the transaction is accounted for as an asset acquisition rather than a business combination. An asset acquisition does not result in the recognition of goodwill and transaction costs are capitalized as part of the cost of the asset or group of assets acquired. Transaction costs allocated to in-process research and development technology with no future alternate use is expensed as incurred. The total consideration is allocated to the various intangible assets acquired on a relative fair value basis. Cash paid in connection of purchase of in-process research and development technology in an asset acquisition is presented within the investing section of the condensed consolidated statement of cash flows.
Goodwill and Intangible Assets, net	Goodwill and Intangible Assets, net Intangible assets related to in-process research and development costs (“IPR&D”) acquired in a business combination are considered to be indefinite-lived until the completion or abandonment of the associated research and development efforts. If and when development is complete, the associated assets would be deemed finite-lived and would then be amortized based on their respective estimated useful lives at that point in time. Prior to completion of the research and development efforts, the assets are considered indefinite-lived. During this period, the assets will not be amortized but will be tested for impairment on an annual basis and between annual tests if we become aware of any events occurring or changes in circumstances that would indicate a reduction in the fair value of the IPR&D projects below their respective carrying amounts. Goodwill represents the excess of the purchase price over the fair value of net identifiable assets and liabilities. Goodwill and IPR&D are not amortized but are tested for impairment at least annually during the fourth fiscal quarter, or if circumstances indicate their value may no longer be recoverable. The Company continues to operate in one segment, which is considered to be the sole reporting unit and, therefore, goodwill was tested for impairment at the enterprise level. As of June 30, 2021, there has been no impairment of goodwill or IPR&D. Intangible assets are carried at cost, net of accumulated amortization. The Company does not have intangible assets with indefinite useful lives other than goodwill and the acquired IPR&D. Amortization is recorded on a straight-line basis over the intangible asset's useful life, which is approximately 6—12 years.
Leases	Leases The Company determines if an arrangement contains a lease at inception. Operating lease right-of-use (“ROU”) assets and operating leases liabilities are recognized based on the present value of the future minimum lease payments over the lease term at the commencement date. ROU assets also include any initial direct costs incurred and any lease payments made at or before the lease commencement date, less lease incentives received or receivable. The Company uses its incremental borrowing rate based on the information available at the commencement date in determining the lease liabilities, as the Company's leases generally do not provide an implicit rate. Lease terms may include options to extend or terminate when the Company is reasonably certain the option will be exercised. Lease expense is recognized on a straight-line basis over the lease term. The Company also has lease arrangements with lease and non-lease components. The Company elected the practical expedient not to separate non-lease components from lease components for the Company’s facility leases. The Company also elected to apply the short-term lease measurement and recognition exemption in which ROU assets and lease liabilities are not recognized for leases with terms of 12 months or less.
Convertible Senior Notes	Convertible Senior Notes In accounting for the issuance of the convertible senior notes, the Company separates the notes into 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, using a discounted cash flow model with a risk adjusted yield. The carrying amount of the equity component representing the conversion option is determined by deducting the fair value of the liability component from the par value of the notes as a whole. This difference represents a debt discount that is amortized to interest expense using the effective interest method over the term of the notes. The equity component is not remeasured as long as it continues to meet the conditions for equity classification. In accounting for the transaction costs related to the issuance of the notes, the Company allocated the total amount incurred to the liability and equity components based on their relative fair values. Transaction costs attributable to the liability component are netted with the liability component and amortized to interest expense using the effective interest method over the term of the notes. Transaction costs attributable to the equity component are netted with the equity component of the notes in additional paid-in capital in the condensed consolidated balance sheets. Starting January 1, 2021, upon early adoption of ASU 2020-06, Accounting for Convertible Instruments and Contracts in an Entity’s Own Equity, the carrying amount of the equity component of the cash conversion feature including the allocated debt issuance costs were reclassified from additional paid-in capital to convertible senior notes, net.
Revenue Recognition	Revenue Recognition The Company derives revenue from the provision of precision oncology testing services provided to its ordering physicians and biopharmaceutical customers, as well as from biopharmaceutical research and development services provided to its biopharmaceutical customers. Precision oncology testing services include genomic profiling and the delivery of other genomic information derived from the Company’s platform. Development services and other include companion diagnostic development, clinical trial setup, monitoring and maintenance, information solutions and laboratory services, and other miscellaneous revenue streams. The Company currently receives payments from third-party commercial and governmental payers, certain hospitals and oncology centers and individual patients, as well as biopharmaceutical companies, research institutes and international distributors. Revenues are recognized when control of services is transferred to customers, in an amount that reflects the consideration the Company expects to be entitled to in exchange for those services. ASC 606 provides for a five-step model that includes identifying the contract with a customer, identifying the performance obligations in the contract, determining the transaction price, allocating the transaction price to the performance obligations, and recognizing revenue when, or as, an entity satisfies a performance obligation. Precision oncology testing The Company recognizes revenue from the sale of its precision oncology tests for clinical customers, including certain hospitals, cancer centers, other institutions and patients, at the time results of the test are reported to physicians. Most precision oncology tests requested by clinical customers are sold without a written agreement; however, the Company determines an implied contract exists with its clinical customers. The Company identifies each sale of its liquid biopsy test to clinical customer as a single performance obligation. With the exception of certain limited contracted arrangements with insurance carriers and other institutions where the transaction price is fixed, a stated contract price does not exist and the transaction price for each implied contract with clinical customers represents variable consideration. The Company estimates the variable consideration under the portfolio approach and considers the historical reimbursement data from third-party commercial and governmental payers and patients, as well as known or anticipated reimbursement trends not reflected in the historical data. The Company monitors the estimated amount to be collected in the portfolio at each reporting period based on actual cash collections in order to assess whether a revision to the estimate is required. Both the estimate and any subsequent revision contain uncertainty and require the use of significant judgment in the estimation of the variable consideration and application of the constraint for such variable consideration. The Company analyzes its actual cash collections over the expected reimbursement period and compares it with the estimated variable consideration for each portfolio and any difference is recognized as an adjustment to estimated revenue after the expected reimbursement period, subject to assessment of the risk of future revenue reversal. For the three months ended June 30, 2021, and 2020, the Company recorded $9.6 million and $9.1 million as revenue, respectively, resulting from cash collections over the expected reimbursement period exceeding the estimated variable consideration related to samples processed in previous periods, including revenue received from successful appeals of reimbursement denials, net of recoupments. For the six months ended June 30, 2021, and 2020, the Company recorded $14.6 million and $16.5 million as revenue, respectively, resulting from cash collections over the expected reimbursement period exceeding the estimated variable consideration related to samples processed in previous periods, including revenue received from successful appeals of reimbursement denials, net of recoupments. Revenue from sales of precision oncology tests to biopharmaceutical customers are based on a negotiated price per test or on the basis of an agreement to provide certain testing volume over a defined period. The Company identifies its promise to transfer a series of distinct liquid biopsy tests to biopharmaceutical customers as a single performance obligation. Precision oncology tests to biopharmaceutical customers are generally billed at a fixed price for each test performed. For agreements involving testing volume to be satisfied over a defined period, revenue is recognized over time based on the number of tests performed as the performance obligation is satisfied over time. Results of the Company’s precision oncology services are delivered electronically, and as such there are no shipping or handling fees incurred by the Company or billed to customers. Development services and other The Company performs development services for its biopharmaceutical customers utilizing its precision oncology information platform. Development services typically represent a single performance obligation as the Company performs a significant integration service, such as analytical validation and regulatory submissions. The individual promises are not separately identifiable from other promises in the contracts and, therefore, are not distinct. However, under certain contracts, a biopharmaceutical customer may engage the Company for multiple distinct development services which are both capable of being distinct and separately identifiable from other promises in the contracts and, therefore, distinct performance obligations. The Company collaborates with pharmaceutical companies in the development of new drugs. As part of these collaborations, the Company provides services related to regulatory filings to support companion diagnostic device submissions for the Company’s liquid biopsy panels. Under these collaborations, the Company generates revenue from achievement of milestones, as well as provision of on-going support. For development services performed, the Company is compensated through a combination of an upfront fee and performance-based, non-refundable regulatory and other developmental milestone payments. The transaction price of the Company's development services contracts typically represents variable consideration. Application of the constraint for variable consideration to milestone payments is an area that requires significant judgment. The Company evaluates factors such as the scientific, clinical, regulatory, commercial, and other risks that must be managed to achieve the respective milestone and the level of effort and investment required to achieve the respective milestone. In making this assessment, the Company considers its historical experience with similar milestones, the degree of complexity and uncertainty associated with each milestone, and whether achievement of the milestone is dependent on parties other than the Company. The constraint for variable consideration is applied such that it is probable a significant reversal of revenue will not occur when the uncertainty associated with the contingency is resolved. Application of the constraint for variable consideration is assessed and updated at each reporting period as a revision to the estimated transaction price. The Company recognizes development services revenue over the period in which biopharmaceutical research and development services are provided. Specifically, the Company recognizes revenue using an input method to measure progress, utilizing costs incurred to-date relative to total expected costs as its measure of progress. The Company assesses the changes to the total expected cost estimates as well as any incremental fees negotiated resulting from changes to the scope of the original contract in determining the revenue recognition at each reporting period. For development of new products or services under these arrangements, costs incurred before technological feasibility is reached are included as research and development expenses in the Company’s condensed consolidated statements of operations, while costs incurred thereafter are recorded as cost of development services and other. The Company also has other miscellaneous revenue streams that are recognized in addition to development services noted above such as clinical trial setup, monitoring and maintenance, referral fees, liquid biopsy testing development and support, GuardantConnect, GuardantINFORM and Guardant-19, and kits fulfillment related revenues. Revenues related to clinical trial setup, monitoring and maintenance, referral fees, liquid biopsy testing development and support, GuardantConnect, GuardantINFORM are generally recognized over time based on an input method to measure progress in the period when the associated services have been performed. Guardant-19 and kits fulfillment related revenues are recognized when such products are delivered. Contracts with multiple performance obligations Contracts with biopharmaceutical customers may include multiple distinct performance obligations, such as provision of precision oncology testing, biopharmaceutical research and development services, and clinical trial enrollment assistance, among others. The Company evaluates the terms and conditions included within its contracts with biopharmaceutical customers to ensure appropriate revenue recognition, including whether services are considered distinct performance obligations that should be accounted for separately versus together. The Company first identifies material promises, in contrast to immaterial promises or administrative tasks, under the contract, and then evaluates whether these promises are both capable of being distinct and distinct within the context of the contract. In assessing whether a promised service is capable of being distinct, the Company considers whether the customer could benefit from the service either on its own or together with other resources that are readily available to the customer, including factors such as the research, development, and commercialization capabilities of a third party as well as the availability of the associated expertise in the general marketplace. In assessing whether a promised service is distinct within the context of the contract, the Company considers whether it provides a significant integration of the services, whether the services significantly modify or customize one another, or whether the services are highly interdependent or interrelated. For contracts with multiple performance obligations, the transaction price is allocated to the separate performance obligations on a relative standalone selling price basis. The Company determines standalone selling price by considering the historical selling price of these performance obligations in similar transactions as well as other factors, including, but not limited to, the price that customers in the market would be willing to pay, competitive pricing of other vendors, industry publications and current pricing practices, and expected costs of satisfying each performance obligation plus appropriate margin. Deferred revenue Deferred revenue, which is a contract liability, consists primarily of payments received in advance of revenue recognition from contracts with customers. For example, development services and other contracts with biopharmaceutical customers often contain upfront payments which results in the recording of deferred revenue to the extent cash is received prior to the Company's performance of the related services. Contract liabilities are relieved as the Company performs its obligations under the contract and revenue is consequently recognized. As of June 30, 2021, and December 31, 2020, the deferred revenue balance was $8.5 million and $8.6 million, respectively, which included $2.9 million and $3.0 million, respectively, related to collaboration development efforts with pharmaceutical companies to be recognized as the Company performs research and development services in the future periods. Revenue recognized in the six months ended June 30, 2021, that was included in the deferred revenue balance as of December 31, 2020, was $6.4 million, of which $3.0 million represented revenue from provision of development services under the collaboration agreements with biopharmaceutical customers. Revenue recognized in the six months ended June 30, 2020, that was included in the deferred revenue balance as of December 31, 2019, was $7.6 million, which primarily represented revenue from provision of development services under the collaboration agreements with biopharmaceutical customers. Transaction price allocated to the remaining performance obligations Transaction price allocated to remaining performance obligations represents contracted revenue that has not yet been recognized, which includes deferred revenue and non-cancelable amounts that will be invoiced and recognized as revenues in future periods. The Company expects to recognize substantially all of the remaining transaction price in the next 12 months.
Costs of Precision Oncology Testing	Costs of Precision Oncology Testing Cost of precision oncology testing generally consists of cost of materials, direct labor including bonus, benefit and stock-based compensation, equipment and infrastructure expenses associated with processing liquid biopsy test samples (including sample accessioning, library preparation, sequencing, quality control analyses and shipping charges to transport blood samples), freight, curation of test results for physicians and license fees due to third parties. Infrastructure expenses include depreciation of laboratory equipment, rent costs, amortization of leasehold improvements and information technology costs. Costs associated with performing the Company’s tests are recorded as the tests are performed regardless of whether revenue was recognized with respect to that test. Royalties for licensed technology calculated as a percentage of revenues generated using the associated technology are recorded as expense at the time the related revenues are recognized. One-time royalty payments related to signing of license agreements or other milestones, such as issuance of new patents, are amortized to expense over the expected useful life of the applicable patent rights.
Cost of Development Services	Cost of Development Services and Other Cost of development service and other primarily includes costs incurred for the performance of development services requested by the Company’s biopharmaceutical customers and other revenues included as noted above. For development of new products, costs incurred before technological feasibility has been achieved are reported as research and development expenses, while costs incurred thereafter are reported as cost of development services and other.
Research and Development Expenses	Research and Development Expenses Research and development expenses are comprised of costs incurred to develop technology and include compensation and benefits, reagents and supplies used in research and development laboratory work, infrastructure expenses, including allocated facility occupancy and information technology costs, contract services and other outside costs. Research and development costs are expensed as incurred. Payments made prior to the receipt of goods or services to be used in research and development are deferred and recognized as expense in the period in which the related goods are received or services are rendered. Costs to develop the Company’s technology capabilities are recorded as research and development unless they meet the criteria to be capitalized as internal-use software costs.
Stock-Based Compensation	Stock-Based Compensation Stock-based compensation related to stock options granted to the Company’s and the Joint Venture's employees, directors and nonemployees 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. Compensation expense for stock options with performance metrics is calculated based upon expected achievement of the metrics specified in the grant. The Company uses the Black-Scholes option-pricing model to estimate the fair value of stock options granted under the 2012 Stock Plan, the 2018 Incentive Award Plan, and the Joint Venture's 2020 Equity Incentive Plan, and stock purchase rights granted under the 2018 Employee Stock Purchase Plan. The Black-Scholes option-pricing model requires assumptions to be made related to the expected term of an award, expected volatility, risk-free rate and expected dividend yield. The board of directors of the Joint Venture has determined the fair value of common stock of the Joint Venture. Forfeitures are accounted for as they occur. For market-based restricted stock units, the Company derives the requisite service period using the Monte Carlo simulation model and the related compensation expense is recognized over the derived service period using an accelerated attribution model commencing on the grant date. Stock-based compensation expense will be recorded regardless of whether the market conditions are achieved or not. If the related market condition is achieved earlier than its estimated derived service period, the stock-based compensation expense will be accelerated, and a cumulative catch-up expense will be recorded during the period in which the market condition is met.
Net Loss Per Share Attributable to Common Shareholders	Net Loss Per Share Attributable to Common Stockholders The Company calculates basic net loss per share attributable to common stockholders by dividing the net loss attributable to common stockholders by the weighted-average number of shares of common stock outstanding for the period. The diluted net loss per share attributable to common stockholders is computed by giving effect to all potential dilutive common stock equivalents outstanding for the period determined using the treasury stock method or the as-if converted method, as appropriate. For purposes of this calculation, stock options, restricted stock units, shares issuable pursuant to the employee stock purchase plan, shares subject to repurchase from early exercised options and contingently issuable shares under the convertible senior notes are considered common stock equivalents but have been excluded from the calculation of diluted net loss per share attributable to common stockholders as their effect is anti-dilutive.
Accounting Pronouncements Adopted	Accounting Pronouncements Adopted Convertible Instruments and Contracts in an Entity’s Own Equity In August 2020, the FASB issued ASU No. 2020-06, Accounting for Convertible Instruments and Contracts in an Entity’s Own Equity (ASU 2020-06) , which simplifies the accounting for certain financial instruments with characteristics of liabilities and equity, including convertible instruments and contracts in an entity’s own equity. Among other changes, ASU 2020-06 removes the liability and equity separation model for convertible instruments with a cash conversion feature, and as a result, after adoption, entities will no longer separately present in equity an embedded conversion feature for such debt. Similarly, the embedded conversion feature will no longer be amortized as interest expense over the life of the instrument. Instead, entities will account for a convertible debt instrument wholly as debt unless (1) a convertible instrument contains features that require bifurcation as a derivative under ASC Topic 815, Derivatives and Hedging, or (2) a convertible debt instrument was issued at a substantial premium. Among other potential impacts, this change is expected to reduce reported interest expense, increase reported net income, and result in a reclassification of certain conversion feature balance sheet amounts from stockholders’ equity to liabilities as it relates to the Company’s convertible senior notes. Additionally, ASU 2020-06 requires the application of the if-converted method to calculate the impact of convertible instruments on diluted earnings per share. The Company early adopted ASU 2020-06 in the first quarter of fiscal 2021 using the modified retrospective approach which resulted in the re-classification of the carrying amount of the equity component of the cash conversion feature including the allocated debt issuance costs as of December 31, 2020 from additional paid-in capital to convertible senior notes, net.
Fair Value Measurements	Financial instruments consist of cash equivalents, marketable securities, accounts receivable, net, prepaid expenses and other current assets, net, accounts payable and accrued expenses. Cash equivalents and marketable securities are stated at fair value. Prepaid expenses and other current assets, net, accounts payable and accrued expenses are stated at their carrying value, which approximates fair value due to the short time to the expected receipt or payment date. Fair value is defined as the exchange price that would be received from sale of an asset or paid to transfer a liability in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. The identification of market participant assumptions provides a basis for determining what inputs are to be used for pricing each asset or liability. A financial instrument’s classification within the fair value hierarchy is based upon the lowest level of input that is significant to the fair value measurement. A fair value hierarchy has been established which gives precedence to fair value measurements calculated using observable inputs over those using unobservable inputs. This hierarchy prioritized the inputs into three broad levels as follows: Level 1 - Quoted prices in active markets for identical assets or liabilities. Level 2 - Inputs other than Level 1 that are observable, either directly or indirectly, such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. Level 3 - Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	6 Months Ended
	Jun. 30, 2021
Accounting Policies [Abstract]
Schedules of Concentration of Risk, by Risk Factor	A significant customer is a biopharmaceutical customer or a clinical testing payer that represents 10% or more of the Company’s total revenue or accounts receivable balance. Revenue attributable to each significant customer, including its affiliated entities, as a percentage of the Company’s total revenue, for the respective period, and accounts receivable balance attributable to each significant customers, including its affiliated entities, as a percentage of the Company’s total accounts receivable balance, at the respective condensed consolidated balance sheet date, are as follows: Revenue Accounts Receivable, Net Three Months Ended June 30, Six Months Ended June 30, June 30, 2021 December 31, 2020 2021 2020 2021 2020 (unaudited) (unaudited) Customer A * * * 14 % * 11 % Customer B 29 % 23 % 27 % 21 % * 13 % Customer C * 10 % * * * 12 % Customer D * * * * 16 % 11 % * less than 10%
Schedule of Contractual Receivables and Related Credit Loss	The following table presents the receivable and the related credit loss amounts: Gross Amount Allowance for Credit Losses Net Amount June 30, 2021 December 31, 2020 Three and Six Months Ended June 30, 2021 June 30, 2021 December 31, 2020 Beginning Balance Charged to (Reversed from) Other Income (Expense), Net Reclassi-fication Ending Balance (unaudited) (unaudited) (unaudited) (in thousand) Prepaid expenses and other current assets $ 1,100 $ — $ — $ — $ (1,100) $ (1,100) $ — $ — Other assets 5,900 7,000 (7,000) — 1,100 (5,900) — $ —

Condensed Consolidated Balanc_4

Condensed Consolidated Balance Sheet Components (Tables)	6 Months Ended
	Jun. 30, 2021
Balance Sheet Related Disclosures [Abstract]
Schedule of Property, Plant and Equipment	Property and equipment, net consist of the following: June 30, 2021 December 31, 2020 (unaudited) (in thousands) Machinery and equipment $ 50,960 $ 40,216 Leasehold improvements 35,542 34,037 Computer hardware 15,929 10,862 Construction in progress 26,892 7,833 Furniture and fixtures 3,591 3,043 Computer software 1,094 1,136 Property and equipment, gross $ 134,008 $ 97,127 Less: accumulated depreciation (44,271) (34,345) Property and equipment, net $ 89,737 $ 62,782
Schedule of Accrued Liabilities	Accrued expenses consist of the following: June 30, 2021 December 31, 2020 (unaudited) (in thousands) Operating lease liabilities $ 7,547 $ 6,632 Accrued tax liabilities 4,500 4,634 Accrued professional services 6,564 3,397 Accrued clinical trials and studies 2,625 1,264 Accrued legal expenses 2,081 2,875 Purchases of property and equipment included in accrued expenses 2,383 1,156 Accrued royalty obligations 179 146 Others 6,119 2,535 Total accrued expenses $ 31,998 $ 22,639

Fair Value Measurements, Cash_2

Fair Value Measurements, Cash Equivalents and Marketable Securities (Tables)	6 Months Ended
	Jun. 30, 2021
Fair Value Disclosures [Abstract]
Schedule of Fair Value Measurements, Recurring and Nonrecurring	The Company’s financial assets and liabilities subject to fair value measurements on a recurring basis and the level of inputs used in such measurements were as follows: June 30, 2021 Fair Value Level 1 Level 2 Level 3 (unaudited) (in thousands) Financial Assets: Money market funds $ 838,114 $ 838,114 $ — $ — Total cash equivalents $ 838,114 $ 838,114 $ — $ — U.S. government debt securities $ 853,072 $ — $ 853,072 $ — Total short-term marketable securities $ 853,072 $ — $ 853,072 $ — U.S. government debt securities $ 55,368 $ — $ 55,368 $ — Total long-term marketable securities $ 55,368 $ — $ 55,368 $ — Total $ 1,746,554 $ 838,114 $ 908,440 $ — Financial Liabilities: Contingent consideration $ 2,120 $ — $ — $ 2,120 Total $ 2,120 $ — $ — $ 2,120 December 31, 2020 Fair Value Level 1 Level 2 Level 3 (in thousands) Financial Assets: Money market funds $ 620,630 $ 620,630 $ — $ — Total cash equivalents $ 620,630 $ 620,630 $ — $ — U.S. government debt securities $ 961,902 $ — $ 961,902 $ — Total short-term marketable securities $ 961,902 $ — $ 961,902 $ — U.S. government debt securities $ 246,597 $ — $ 246,597 $ — Total long-term marketable securities $ 246,597 $ — $ 246,597 $ — Total $ 1,829,129 $ 620,630 $ 1,208,499 $ — Financial Liabilities: Contingent consideration $ 1,245 $ — $ — $ 1,245 Total $ 1,245 $ — $ — $ 1,245
Schedule of Level 3 Activity	The following table summarizes the activities for the Level 3 financial instruments for the three and six months ended June 30, 2021, and 2020: Redeemable Noncontrolling Interest Contingent Consideration Three Months Ended June 30, Six Months Ended June 30, Three Months Ended June 30, Six Months Ended June 30, 2021 2020 2021 2020 2021 2020 2021 2020 (unaudited) (in thousands) Fair value — beginning of period $ 59,400 $ 45,500 $ 57,100 $ 49,600 $ 1,245 $ 1,175 $ 1,245 $ 1,365 Increase (decrease) in fair value 1,645 6,186 5,932 3,159 875 — 875 (190) Net loss for the period (1,645) (1,286) (3,632) (2,359) — — — — Fair value — end of period $ 59,400 $ 50,400 $ 59,400 $ 50,400 $ 2,120 $ 1,175 $ 2,120 $ 1,175
Schedule of Debt Securities, Available-for-sale	The following tables summarizes the Company’s cash equivalents and marketable securities’ amortized costs, gross unrealized gains, gross unrealized losses and estimated fair values by significant investment category: June 30, 2021 Amortized Cost Gross Unrealized Gain Gross Unrealized Loss Estimated Fair Value (unaudited) (in thousands) Money market fund $ 838,114 $ — $ — $ 838,114 U.S. government debt securities 907,832 613 (5) 908,440 Total $ 1,745,946 $ 613 $ (5) $ 1,746,554 December 31, 2020 Amortized Cost Gross Unrealized Gain Gross Unrealized Loss Estimated Fair Value (in thousands) Money market fund $ 620,630 $ — $ — $ 620,630 U.S. government debt securities 1,206,195 2,339 (35) 1,208,499 Total $ 1,826,825 $ 2,339 $ (35) $ 1,829,129

Intangible Assets, Net and Go_2

Intangible Assets, Net and Goodwill (Tables)	6 Months Ended
	Jun. 30, 2021
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Finite-Lived Intangible Assets	The following table presents details of purchased intangible assets as of June 30, 2021, and December 31, 2020: June 30, 2021 Gross Carrying Amount Accumulated Amortization Net Carrying Amount Remaining Weighted Average Useful Life (unaudited) (in thousands) (in years) Intangible assets subject to amortization: Acquired license $ 11,886 $ (1,915) $ 9,971 9.3 Non-compete agreements and other covenant rights 5,100 (1,482) 3,618 4.4 Total intangible assets subject to amortization 16,986 (3,397) 13,589 Intangible assets not subject to amortization: IPR&D 1,600 — 1,600 Goodwill 3,290 — 3,290 Total purchased intangible assets $ 21,876 $ (3,397) $ 18,479 December 31, 2020 Gross Carrying Amount Accumulated Amortization Net Carrying Amount Remaining Weighted Average Useful Life (in thousands) (in years) Intangible assets subject to amortization: Acquired license $ 11,886 $ (1,367) $ 10,519 9.8 Non-compete agreements 5,100 (1,064) 4,036 4.9 Total intangible assets subject to amortization 16,986 (2,431) 14,555 Intangible assets not subject to amortization: IPR&D 1,600 — 1,600 Goodwill 3,290 — 3,290 Total purchased intangible assets $ 21,876 $ (2,431) $ 19,445
Schedule of Indefinite-Lived Intangible Assets	The following table presents details of purchased intangible assets as of June 30, 2021, and December 31, 2020: June 30, 2021 Gross Carrying Amount Accumulated Amortization Net Carrying Amount Remaining Weighted Average Useful Life (unaudited) (in thousands) (in years) Intangible assets subject to amortization: Acquired license $ 11,886 $ (1,915) $ 9,971 9.3 Non-compete agreements and other covenant rights 5,100 (1,482) 3,618 4.4 Total intangible assets subject to amortization 16,986 (3,397) 13,589 Intangible assets not subject to amortization: IPR&D 1,600 — 1,600 Goodwill 3,290 — 3,290 Total purchased intangible assets $ 21,876 $ (3,397) $ 18,479 December 31, 2020 Gross Carrying Amount Accumulated Amortization Net Carrying Amount Remaining Weighted Average Useful Life (in thousands) (in years) Intangible assets subject to amortization: Acquired license $ 11,886 $ (1,367) $ 10,519 9.8 Non-compete agreements 5,100 (1,064) 4,036 4.9 Total intangible assets subject to amortization 16,986 (2,431) 14,555 Intangible assets not subject to amortization: IPR&D 1,600 — 1,600 Goodwill 3,290 — 3,290 Total purchased intangible assets $ 21,876 $ (2,431) $ 19,445
Schedule of Finite-Lived Intangible Assets, Future Amortization Expense	The following table summarizes estimated future amortization expense of finite-lived intangible assets—net: Year Ending December 31, (unaudited) (in thousands) Remainder of 2021 $ 982 2022 1,947 2023 1,947 2024 1,952 2025 1,705 2026 and thereafter 5,056 Total $ 13,589

Debt (Tables)

Debt (Tables)	6 Months Ended
	Jun. 30, 2021
Debt Disclosure [Abstract]
Schedule of Long-term Debt Instrument Components	The following table sets forth the components of the 2027 Notes as of June 30, 2021, and December 31, 2020: June 30, 2021 December 31, 2020 (unaudited) (in thousands) Liability component: Principal $ 1,150,000 $ 1,150,000 Less: debt discount, net of amortization — (331,074) Less: debt issuance costs, net of amortization (16,461) (12,634) Net carrying amount $ 1,133,539 $ 806,292 Equity component recorded at issuance: 2027 Notes $ — $ 335,667 Less: issuance costs — (5,264) Net amount recorded in equity $ — $ 330,403

Leases (Tables)

Leases (Tables)	6 Months Ended
	Jun. 30, 2021
Leases [Abstract]
Lease Information	June 30, 2021 December 31, 2020 (unaudited) Weighted-average remaining lease term (in years) 10.3 5.5 Weighted-average discount rate 4.14 % 8.07 %
Schedule of Operating Lease Liability Maturities	The following table summarizes the Company's future principal contractual obligations for operating lease commitments as of June 30, 2021: Year Ending December 31, (unaudited) (in thousands) Remainder of 2021 $ 5,398 2022 21,454 2023 28,976 2024 31,529 2025 32,084 2026 and thereafter 177,402 Total operating lease payments $ 296,843 Less: imputed interest (54,792) Less: lease incentives (22,721) Total operating lease liabilities $ 219,330

Common Stock (Tables)

Common Stock (Tables)	6 Months Ended
	Jun. 30, 2021
Equity [Abstract]
Schedule of Stock by Class	The Company’s common stock has been reserved for the following potential future issuances: June 30, 2021 December 31, 2020 (unaudited) Shares underlying outstanding stock options 2,703,906 3,101,181 Shares underlying unvested restricted stock units 1,155,370 1,118,655 Market-based restricted stock units 2,260,764 3,391,148 Performance-based restricted stock units 415,535 377,922 Shares available for issuance under the 2018 Incentive Award Plan 5,928,052 1,819,223 Shares available for issuance under the 2018 Employee Stock Purchase Plan 1,475,593 1,536,491 Total 13,939,220 11,344,620

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	6 Months Ended
	Jun. 30, 2021
Share-based Payment Arrangement [Abstract]
Schedule of Share-based Compensation, Stock Options, Activity	A summary of the Company’s stock option activity under the 2012 Stock Plan (as amended and restated, the “2012 Plan”) and the 2018 Incentive Award Plan (the “2018 Plan”) and related information is as follows: Options Outstanding Shares Shares Subject to Options Outstanding Weighted-Average Exercise Price Weighted-Average Remaining Contractual Life (Years) Aggregate Intrinsic Value (unaudited) (in thousands) Balance as of December 31, 2020 1,819,223 3,101,181 $ 15.80 6.9 $ 350,670 2018 Plan annual increase (1) 3,689,000 — Granted (60,677) 60,677 142.73 Exercised — (371,711) 14.34 Canceled 42,956 (86,241) 47.02 Restricted stock units granted (177,166) — — Restricted stock units canceled 94,075 — — Market-based restricted stock units canceled 558,254 — — Performance-based restricted stock units granted (52,917) — — Performance-based restricted stock units canceled 15,304 — — Balance as of June 30, 2021 5,928,052 2,703,906 $ 17.86 6.5 $ 288,749 Vested and Exercisable as of June 30, 2021 2,091,339 $ 9.16 6.1 $ 240,569 (1) Effective as of January 1, 2021, an additional 3,689,000 shares of common stock became available for issuance under the 2018 Plan, as a result of the operation of an automatic annual increase provision therein. A summary of the Joint Venture's stock option activity under the AMEA 2020 Plan and related information is as follows: Options Outstanding Shares Shares Subject to Options Outstanding Weighted-Average Exercise Price Weighted-Average Remaining Contractual Life (Years) Aggregate Intrinsic Value (unaudited) (in thousands) Balance as of December 31, 2020 542,220 4,053,335 $ 0.58 9.6 $ — Granted (382,223) 382,223 0.58 Exercised — (91,109) 0.58 Canceled 92,412 (92,412) 0.58 Balance as of June 30, 2021 252,409 4,252,037 $ 0.58 9.2 $ — Vested and Exercisable as of June 30, 2021 2,352,180 $ 0.58 9.1 $ —
Schedule of Restricted Stock Activity	A summary of the Company’s restricted stock unit activity excluding the performance-based and market-based restricted stock units under the 2012 Plan and the 2018 Plan and related information is as follows: Restricted Stock Units Outstanding Weighted-Average Grant Date Fair Value (unaudited) Balance as of December 31, 2020 1,118,655 $ 92.89 Granted 177,166 154.94 Vested and released (46,376) 80.32 Canceled (94,075) 92.67 Balance as of June 30, 2021 1,155,370 $ 102.93 A summary of the Company’s performance-based restricted stock unit activity under the 2018 Plan and related information is as follows: Performance-based Restricted Stock Units Outstanding Weighted-Average Grant Date Fair Value (unaudited) Balance as of December 31, 2020 377,922 $ 113.40 Granted 52,917 135.94 Canceled (15,304) 113.40 Balance as of June 30, 2021 415,535 $ 116.27 Market-based Restricted Stock Units Outstanding Weighted-Average Grant Date Fair Value (unaudited) Balance as of December 31, 2020 3,391,148 $ 67.00 Vested and released (572,130) 70.58 Canceled (1) (558,254) 70.58 Balance as of June 30, 2021 2,260,764 $ 65.20 (1) Represented shares withheld by the Company for MSU holders' tax obligation upon release of vested MSUs.
Schedule of Performance-based Restricted Stock Units Vesting Conditions	The following table presents additional information relating to each MSU award: Tranche Price Goal Number of RSUs Tranche 1 $120 per share 565,192 Tranche 2 $150 per share 565,191 Tranche 3 $200 per share 565,191
Schedule of Compensation Cost for Share-based Payment Arrangements, Allocation of Share-based Compensation Costs by Plan	The following table presents the effect of employee and non-employee related stock-based compensation expense including the Joint Venture: Three Months Ended Six Months Ended 2021 2020 2021 2020 (unaudited) (in thousands) Cost of precision oncology testing $ 873 $ 407 $ 1,640 $ 710 Research and development expense 4,564 2,622 8,864 4,986 Sales and marketing expense 3,438 2,167 6,318 3,965 General and administrative expense 25,632 20,619 72,754 22,492 Total stock-based compensation expense $ 34,507 $ 25,815 $ 89,576 $ 32,153
Schedule of Share-based Payment Award, Employee Stock Purchase Plan, Valuation Assumptions	The grant date fair value of stock options was estimated using a Black-Scholes option-pricing model with the following weighted-average assumptions including the Joint Venture: Three Months Ended Six Months Ended 2021 2020 2021 2020 (unaudited) Expected term (in years) 5.49 – 6.04 5.50 – 6.10 5.49 – 6.04 5.50 – 6.10 Expected volatility 63.6% – 66.7% 66.5% – 68.5% 63.6% – 66.7% 66.5% – 73.3% Risk-free interest rate 0.3% – 1.1% 0.4% – 0.4% 0.3% – 1.1% 0.4% – 1.6% Expected dividend yield —% —% —% —% The grant date fair value of the stock purchase right granted under the ESPP was estimated using a Black-Scholes option-pricing model with the following weighted-average assumptions: Three and Six Months Ended June 30, 2021 2020 (unaudited) Expected term (in years) 0.5 0.5 Expected volatility 50.8% 73.2% Risk-free interest rate —% 0.2% Expected dividend yield —% —%

Net Loss Per Share Attributab_2

Net Loss Per Share Attributable to Guardant Health, Inc. Common Stockholders (Tables)	6 Months Ended
	Jun. 30, 2021
Earnings Per Share [Abstract]
Schedule of Earnings Per Share, Basic and Diluted	The following table sets forth the computation of the basic and diluted net loss per share attributable to Guardant Health, Inc. common stockholders: Three Months Ended Six Months Ended 2021 2020 2021 2020 (unaudited) (in thousands, except per share data) Net loss $ (97,575) $ (49,739) $ (204,933) $ (81,568) Adjustment of redeemable noncontrolling interest — (4,900) (2,300) (800) Net loss attributable to Guardant Health, Inc. common stockholders, basic and diluted $ (97,575) $ (54,639) $ (207,233) $ (82,368) Net loss per share attributable to Guardant Health, Inc. common stockholders, basic and diluted $ (0.96) $ (0.57) $ (2.05) $ (0.87) Weighted-average shares used in computing net loss per share attributable to Guardant Health, Inc. common stockholders, basic and diluted 101,172 96,011 101,064 95,196
Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share	The following weighted-average common stock equivalents were excluded from the calculation of diluted net loss per share attributable to Guardant Health, Inc. common stockholders for the periods presented as they had an anti-dilutive effect: Three Months Ended Six Months Ended 2021 2020 2021 2020 (unaudited) (in thousands) Stock options issued and outstanding (1) 2,720 4,056 2,816 4,200 Restricted stock units 1,147 542 1,133 519 MSUs 2,261 1,342 2,453 671 PSUs 409 — 408 — ESPP obligation 43 37 45 40 Common stock subject to repurchase 8 20 10 21 Convertible senior notes 8,225 — 8,225 — Total 14,813 5,997 15,090 5,451

Segment and Geographic Inform_2

Segment and Geographic Information (Tables)	6 Months Ended
	Jun. 30, 2021
Segment Reporting [Abstract]
Schedule of Segment Reporting Information, by Segment	The following table sets forth the Company’s revenue by geographic areas based on the customers’ locations: Three Months Ended Six Months Ended 2021 2020 2021 2020 (unaudited) (in thousands) United States $ 87,868 $ 61,422 $ 160,168 $ 126,035 International (1) 4,233 4,913 10,598 7,810 Total revenue $ 92,101 $ 66,335 $ 170,766 $ 133,845 (1) No single country outside of the United States accounted for more than 10% of total revenue during the three and six months ended June 30, 2021 and 2020, respectively.

Description of Business (Detail

Description of Business (Details)	May 31, 2018
Guardant Health AMEA, Inc
Subsidiary, Sale of Stock [Line Items]
Ownership interest in joint venture	50.00%

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Narrative (Details) $ in Thousands	1 Months Ended		3 Months Ended		6 Months Ended
	Dec. 31, 2020USD ($)	Aug. 31, 2020USD ($)	Jun. 30, 2021USD ($)	Jun. 30, 2020USD ($)	Jun. 30, 2021USD ($)segment	Jun. 30, 2020USD ($)
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Restricted cash – included in other assets, net			$ 315	$ 0	$ 315	$ 0
Restricted cash	$ 0
Non-marketable equity and other investments	0		13,300		13,300
Impairment or adjustments of non-marketable securities					0
Other receivables and other assets due from a third-party		$ 8,000
Other receivables and other assets, term		6 years
Contractual receivables, installment payment	1,000
Contractual receivables, credit loss	7,000		0		0
Contract asset	15,600		24,800		$ 24,800
Number of operating segments | segment					1
Impairment of goodwill			0		$ 0
Impairment of intangible assets					0
Revenue from cash collections exceeding estimated variable consideration			9,600	$ 9,100	14,600	16,500
Deferred revenue	8,600		8,500		8,500
Deferred revenue recognized					6,400	$ 7,600
Guardant360CDx
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Contract asset	8,400
Collaborative Arrangement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Deferred revenue	$ 3,000		$ 2,900		2,900
Deferred revenue recognized					$ 3,000
Minimum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Useful life (years)					6 years
Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Useful life (years)					12 years

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Schedule of Concentration Risk (Details) - Credit Concentration Risk	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Customer A | Revenue
Concentration Risk [Line Items]
Concentration risk, percentage				14.00%
Customer A | Accounts Receivable, Net
Concentration Risk [Line Items]
Concentration risk, percentage					11.00%
Customer B | Revenue
Concentration Risk [Line Items]
Concentration risk, percentage	29.00%	23.00%	27.00%	21.00%
Customer B | Accounts Receivable, Net
Concentration Risk [Line Items]
Concentration risk, percentage					13.00%
Customer C | Revenue
Concentration Risk [Line Items]
Concentration risk, percentage		10.00%
Customer C | Accounts Receivable, Net
Concentration Risk [Line Items]
Concentration risk, percentage					12.00%
Customer D | Accounts Receivable, Net
Concentration Risk [Line Items]
Concentration risk, percentage			16.00%		11.00%

Summary of Significant Accoun_6

Summary of Significant Accounting Policies - Receivable and Related Credit Loss (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended	6 Months Ended
	Dec. 31, 2020	Jun. 30, 2021	Jun. 30, 2021
Accounting Policies [Abstract]
Financing receivable, gross amount, current	$ 0	$ 1,100	$ 1,100
Financing receivable, net amount, noncurrent	7,000	5,900	5,900
Allowance for Credit Losses
Beginning balance, financing receivable, allowance for credit loss, current		0	0
Additions: charged to other income (expense), net, allowance for credit loss, current		0	0
Reclassification, allowance for credit loss, current		(1,100)	(1,100)
Ending balance, financing receivable, allowance for credit loss, current	0	(1,100)	(1,100)
Beginning balance, financing receivable, allowance for credit loss, noncurrent		(7,000)	(7,000)
Additions: charged to other income (expense), net, allowance for credit loss, noncurrent	(7,000)	0	0
Reclassification, allowance for credit loss, noncurrent		1,100	1,100
Ending balance, financing receivable, allowance for credit loss, noncurrent	(7,000)	(5,900)	(5,900)
Financing receivable, net amount, current	0	0	0
Financing receivable, net amount, noncurrent	$ 0	$ 0	$ 0

Investment in Joint Venture (De

Investment in Joint Venture (Details) - USD ($) $ / shares in Units, $ in Thousands		1 Months Ended		6 Months Ended
		Jun. 30, 2020	May 31, 2018	Jun. 30, 2021	Dec. 31, 2020
Schedule of Equity Method Investments [Line Items]
Common stock, shares authorized (in shares)				350,000,000	350,000,000
Common stock, shares reserved for future issuance (in shares)				13,939,220	11,344,620
Common stock, shares issued (in shares)				101,265,100	100,213,985
Common stock, shares outstanding (in shares)				101,265,100	100,213,985
Assets	[1]			$ 2,291,885	$ 2,271,781
Threshold percentage of fair value that is no less than internal rate of return				20.00%
Fair value of joint venture threshold				40.00%
Variable Interest Entity
Schedule of Equity Method Investments [Line Items]
Assets				$ 27,500	$ 35,000
Guardant Health AMEA, Inc
Schedule of Equity Method Investments [Line Items]
Payments to acquire interest in joint venture			$ 9,000
Equity method investment, shares purchased (in shares)			40,000
Equity method investment, ownership percentage			50.00%
Common stock, shares authorized (in shares)		89,000,000
Guardant Health AMEA, Inc | Class A
Schedule of Equity Method Investments [Line Items]
Common stock, shares authorized (in shares)		80,000,000
Common stock, shares issued (in shares)				0	0
Common stock, shares outstanding (in shares)				0	0
Guardant Health AMEA, Inc | Class B
Schedule of Equity Method Investments [Line Items]
Common stock, shares authorized (in shares)		9,000,000
Common stock, shares issued (in shares)				91,109	0
Common stock, shares outstanding (in shares)				91,109	0
Guardant Health AMEA, Inc | Class B | AMEA 2020 Plan
Schedule of Equity Method Investments [Line Items]
Common stock, shares reserved for future issuance (in shares)		4,595,555
Guardant Health AMEA, Inc | Series A
Schedule of Equity Method Investments [Line Items]
Preferred stock, shares authorized (in shares)		80,000,000
Preferred stock issued (in shares)				80,000,000	80,000,000
Preferred stock dividend rate (in usd per share)		$ 0.05
Preferred stock outstanding (in shares)				80,000,000	80,000,000
Guardant Health AMEA, Inc | Series A | SoftBank
Schedule of Equity Method Investments [Line Items]
Preferred stock issued (in shares)		40,000,000
Guardant Health AMEA, Inc | Series A | Guardant Health, Inc.
Schedule of Equity Method Investments [Line Items]
Preferred stock issued (in shares)		40,000,000
Guardant Health AMEA, Inc | SoftBank
Schedule of Equity Method Investments [Line Items]
Equity method investment, shares purchased (in shares)			40,000
Equity method investment, ownership percentage			50.00%
Redeemable noncontrolling interest, redemption value			$ 41,000
Guardant Health AMEA, Inc | SoftBank | Series A
Schedule of Equity Method Investments [Line Items]
Common stock reclassified and converted into preferred stock (in shares)		1,000
[1]	As of June 30, 2021 and December 31, 2020, this balance includes $27.5 million and $35.0 million of assets, respectively, that can be used only to settle obligations of the consolidated variable interest entity (“VIE”) and VIE’s subsidiaries, and $3.8 million and $4.9 million, respectively, of liabilities of the consolidated VIE and VIE’s subsidiaries, for which their creditors do not have recourse to the general credit of the Company. See Note 3, Investment in Joint Venture .

Condensed Consolidated Balanc_5

Condensed Consolidated Balance Sheet Components - Property, Plant and Equipment (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 134,008	$ 97,127
Less: accumulated depreciation	(44,271)	(34,345)
Property and equipment, net	89,737	62,782
Machinery and equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	50,960	40,216
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, gross	35,542	34,037
Computer hardware
Property, Plant and Equipment [Line Items]
Property and equipment, gross	15,929	10,862
Construction in progress
Property, Plant and Equipment [Line Items]
Property and equipment, gross	26,892	7,833
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Property and equipment, gross	3,591	3,043
Computer software
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 1,094	$ 1,136

Condensed Consolidated Balanc_6

Condensed Consolidated Balance Sheet Components - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Balance Sheet Related Disclosures [Abstract]
Depreciation and amortization expense	$ 5.1	$ 3.2	$ 9.6	$ 6.2

Condensed Consolidated Balanc_7

Condensed Consolidated Balance Sheet Components - Accrued Expenses (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Balance Sheet Related Disclosures [Abstract]
Operating lease liabilities	$ 7,547	$ 6,632
Accrued tax liabilities	4,500	4,634
Accrued professional services	6,564	3,397
Accrued clinical trials and studies	2,625	1,264
Accrued legal expenses	2,081	2,875
Purchases of property and equipment included in accrued expenses	2,383	1,156
Accrued royalty obligations	179	146
Others	6,119	2,535
Total accrued expenses	$ 31,998	$ 22,639

Fair Value Measurements, Cash_3

Fair Value Measurements, Cash Equivalents and Marketable Securities - Measured on Recurring Basis (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	$ 838,114	$ 620,630
Debt securities, short-term	853,072	961,902
Debt securities, long-term	55,368	246,597
Total assets	1,746,554	1,829,129
Initial fair value of contingent consideration at acquisition date	2,120	1,245
Financial and nonfinancial liabilities, fair value disclosure	2,120	1,245
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	838,114	620,630
Debt securities, short-term	0	0
Debt securities, long-term	0	0
Total assets	838,114	620,630
Initial fair value of contingent consideration at acquisition date	0	0
Financial and nonfinancial liabilities, fair value disclosure	0	0
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Debt securities, short-term	853,072	961,902
Debt securities, long-term	55,368	246,597
Total assets	908,440	1,208,499
Initial fair value of contingent consideration at acquisition date	0	0
Financial and nonfinancial liabilities, fair value disclosure	0	0
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Debt securities, short-term	0	0
Debt securities, long-term	0	0
Total assets	0	0
Initial fair value of contingent consideration at acquisition date	2,120	1,245
Financial and nonfinancial liabilities, fair value disclosure	2,120	1,245
U.S. government debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, short-term	853,072	961,902
Debt securities, long-term	55,368	246,597
U.S. government debt securities | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, short-term	0	0
Debt securities, long-term	0	0
U.S. government debt securities | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, short-term	853,072	961,902
Debt securities, long-term	55,368	246,597
U.S. government debt securities | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, short-term	0	0
Debt securities, long-term	0	0
Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	838,114	620,630
Money market funds | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	838,114	620,630
Money market funds | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Money market funds | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	$ 0	$ 0

Fair Value Measurements, Cash_4

Fair Value Measurements, Cash Equivalents and Marketable Securities - Narrative (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2021	Dec. 31, 2020
Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long term maturity period (years)	1 year 3 months 18 days
Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long term maturity period (years)	2 years
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contingent liability from business acquisition	$ 2,120	$ 1,245
Level 3 | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contingent liability from business acquisition	$ 2,120	$ 1,245

Fair Value Measurements, Cash_5

Fair Value Measurements, Cash Equivalents and Marketable Securities - Activity In Level 3 Instruments (Details) - Fair Value, Measurements, Recurring - Level 3 - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Redeemable Noncontrolling Interest
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value — beginning of period	$ 59,400	$ 45,500	$ 57,100	$ 49,600
Increase (decrease) in fair value	1,645	6,186	5,932	3,159
Net loss for the period	(1,645)	(1,286)	(3,632)	(2,359)
Fair value — end of period	59,400	50,400	59,400	50,400
Contingent Consideration
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value — beginning of period	1,245	1,175	1,245	1,365
Increase (decrease) in fair value	875	0	875	(190)
Net loss for the period	0	0	0	0
Fair value — end of period	$ 2,120	$ 1,175	$ 2,120	$ 1,175

Fair Value Measurements, Cash_6

Fair Value Measurements, Cash Equivalents and Marketable Securities - Cash Equivalents and Marketable Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020	Jun. 30, 2020
Debt Securities, Available-for-sale [Line Items]
Cash and cash equivalents	$ 938,590	$ 832,977	$ 164,671
Amortized cost, cash and cash equivalents and debt securities available-for-sale	1,745,946	1,826,825
Gross Unrealized Gain	613	2,339
Gross Unrealized Loss	(5)	(35)
Cash, cash equivalents and debt securities, fair value	1,746,554	1,829,129
Money market funds
Debt Securities, Available-for-sale [Line Items]
Cash and cash equivalents	838,114	620,630
Gross Unrealized Gain	0	0
Gross Unrealized Loss	0	0
Estimated fair value, cash and cash equivalents	838,114	620,630
U.S. government debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized cost, debt securities, available-for-sale	907,832	1,206,195
Gross Unrealized Gain	613	2,339
Gross Unrealized Loss	(5)	(35)
Estimated fair value, debt securities	$ 908,440	$ 1,208,499

Patent License Acquisition (Det

Patent License Acquisition (Details) - USD ($) $ in Thousands	1 Months Ended	6 Months Ended
	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Business Acquisition [Line Items]
Finite-lived intangible assets		$ 16,986		$ 16,986
In process research and development expensed		$ 0	$ 8,500
Minimum
Business Acquisition [Line Items]
Useful life (years)		6 years
Maximum
Business Acquisition [Line Items]
Useful life (years)		12 years
Patent and Covenant Rights | Minimum
Business Acquisition [Line Items]
Useful life (years)	6 years
Patent and Covenant Rights | Maximum
Business Acquisition [Line Items]
Useful life (years)	12 years
KeyGene Patent License Acquisition
Business Acquisition [Line Items]
Payment in connection with a license agreement	$ 18,500
Asset acquisition, transaction costs	600
In process research and development expensed	8,500
Settlement of prior dispute between parties	$ 1,200
KeyGene Patent License Acquisition | Patent and Covenant Rights
Business Acquisition [Line Items]
Finite-lived intangible assets			$ 9,400

Intangible Assets, Net and Go_3

Intangible Assets, Net and Goodwill - Schedule of Intangible Assets by Class (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2021	Dec. 31, 2020
Finite-Lived Intangible Assets [Line Items]
Intangible assets subject to amortization, gross carrying amount	$ 16,986	$ 16,986
Intangible assets subject to amortization, accumulated amortization	(3,397)	(2,431)
Intangible assets subject to amortization, net	13,589	14,555
Goodwill	3,290	3,290
Gross Carrying Amount	21,876	21,876
Net Carrying Amount	18,479	19,445
IPR&D
Finite-Lived Intangible Assets [Line Items]
IPR&D	1,600	1,600
Acquired license
Finite-Lived Intangible Assets [Line Items]
Intangible assets subject to amortization, gross carrying amount	11,886	11,886
Intangible assets subject to amortization, accumulated amortization	(1,915)	(1,367)
Intangible assets subject to amortization, net	$ 9,971	$ 10,519
Remaining Weighted Average Useful Life	9 years 3 months 18 days	9 years 9 months 18 days
Non-compete agreements and other covenant rights
Finite-Lived Intangible Assets [Line Items]
Intangible assets subject to amortization, gross carrying amount	$ 5,100	$ 5,100
Intangible assets subject to amortization, accumulated amortization	(1,482)	(1,064)
Intangible assets subject to amortization, net	$ 3,618	$ 4,036
Remaining Weighted Average Useful Life	4 years 4 months 24 days	4 years 10 months 24 days

Intangible Assets, Net and Go_4

Intangible Assets, Net and Goodwill - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Goodwill and Intangible Assets Disclosure [Abstract]
Amortization of intangible assets	$ 0.5	$ 0.5	$ 1	$ 0.8

Intangible Assets, Net and Go_5

Intangible Assets, Net and Goodwill - Schedule of Future Amortization (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Goodwill and Intangible Assets Disclosure [Abstract]
Remainder of 2021	$ 982
2022	1,947
2023	1,947
2024	1,952
2025	1,705
2026 and thereafter	5,056
Intangible assets subject to amortization, net	$ 13,589	$ 14,555

Debt - Narrative (Details)

Debt - Narrative (Details) $ / shares in Units, $ in Thousands	1 Months Ended	3 Months Ended	6 Months Ended
	Nov. 30, 2020USD ($)d$ / shares	Jun. 30, 2021USD ($)	Jun. 30, 2021USD ($)	Jun. 30, 2020USD ($)	Dec. 31, 2020USD ($)	Nov. 16, 2020$ / shares
Debt Instrument [Line Items]
Amortization of debt issuance costs | $			$ 1,282	$ 0
Notes Hedges, strike price (in dollars per share) | $ / shares						$ 182.60
Share price, premium						75.00%
Common stock share price (in dollars per share) | $ / shares						$ 104.34
Purchase of convertible senior note hedges | $	$ 90,000
Senior Notes Due 2027 | Conversion Period Three
Debt Instrument [Line Items]
Threshold percentage of common stock price trigger	130.00%
Threshold of common stock trading days	20
Threshold of consecutive common stock trading days	30
Senior Notes Due 2027 | Convertible Debt
Debt Instrument [Line Items]
Principal amount | $	$ 1,150,000	$ 1,150,000	1,150,000		$ 1,150,000
Stated interest rate	0.00%
Maximum special interest rate percentage	0.50%
Conversion ratio	0.0071523
Conversion price (in dollars per share) | $ / shares	$ 139.82
Estimated fair value | $		1,300,000	1,300,000		$ 1,300,000
Senior Notes Due 2027 | Convertible Debt | Conversion Period One
Debt Instrument [Line Items]
Threshold percentage of common stock price trigger	130.00%
Threshold of common stock trading days	20
Threshold of consecutive common stock trading days	30
Senior Notes Due 2027 | Convertible Debt | Conversion Period Two
Debt Instrument [Line Items]
Threshold of common stock trading days	5
Threshold of consecutive common stock trading days	10
Minimum percentage of common stock price trigger	98.00%
Senior Notes Due 2027 | Convertible senior notes
Debt Instrument [Line Items]
Amortization of debt issuance costs | $		$ 600	$ 1,300
Effective interest rate of the liability component		0.20%	0.20%

Debt - Components of Convertibl

Debt - Components of Convertible Senior Notes (Details) - Convertible Debt - Senior Notes Due 2027 - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020	Nov. 30, 2020
Debt Instrument [Line Items]
Principal	$ 1,150,000	$ 1,150,000	$ 1,150,000
Less: debt discount, net of amortization	0	(331,074)
Less: debt issuance costs, net of amortization	(16,461)	(12,634)
Net carrying amount	1,133,539	806,292
2027 Notes	0	335,667
Less: issuance costs	0	(5,264)
Net amount recorded in equity	$ 0	$ 330,403

Leases - Narrative (Details)

Leases - Narrative (Details) $ in Millions	1 Months Ended	3 Months Ended		6 Months Ended
	Jul. 31, 2020segment	Jun. 30, 2021USD ($)	Jun. 30, 2020USD ($)	Jun. 30, 2021USD ($)	Jun. 30, 2020USD ($)
Lessee, Lease, Description [Line Items]
Operating lease expense | $		$ 6.9	$ 1.9	$ 10.8	$ 3.4
Office and laboratory space
Lessee, Lease, Description [Line Items]
Number lease agreements, not yet commenced | segment	2
Renewal lease term, lease not yet commenced	10 years
Office and laboratory space | San Diego, California
Lessee, Lease, Description [Line Items]
Lease not yet commenced, term	8 years
Office and laboratory space | Palo Alto, California
Lessee, Lease, Description [Line Items]
Lease not yet commenced, term	12 years
Minimum
Lessee, Lease, Description [Line Items]
Lease term		1 year		1 year
Maximum
Lessee, Lease, Description [Line Items]
Lease term		12 years		12 years

Leases - Lease Information (Det

Leases - Lease Information (Details)	Jun. 30, 2021	Dec. 31, 2020
Leases [Abstract]
Weighted-average remaining lease term (in years)	10 years 3 months 18 days	5 years 6 months
Weighted-average discount rate	4.14%	8.07%

Leases - Schedule of Operating

Leases - Schedule of Operating Liability Maturities (Details) $ in Thousands	Jun. 30, 2021USD ($)
Leases [Abstract]
Remainder of 2021	$ 5,398
2022	21,454
2023	28,976
2024	31,529
2025	32,084
2026 and thereafter	177,402
Total operating lease payments	296,843
Less: imputed interest	(54,792)
Less: lease incentives	(22,721)
Total operating lease liabilities	$ 219,330

Commitments and Contingencies -

Commitments and Contingencies - Narrative (Details)	1 Months Ended
	Mar. 31, 2021patent	Dec. 31, 2020patent	Nov. 30, 2020patent	Jul. 31, 2018segmentpetition	Nov. 30, 2017patent
Other Commitments [Line Items]
Gain contingency, patents allegedly infringed upon, number				4	4
Foundation Medicine, Inc. vs. Guardant Health, Inc.
Other Commitments [Line Items]
Gain contingency, patents allegedly infringed upon, number | patent	2	2	7
Number of petitions filed				6
Number of petitions denied | segment				4
Number of petitions remaining				2

Common Stock (Details)

Common Stock (Details) - USD ($)	1 Months Ended	3 Months Ended	6 Months Ended		12 Months Ended
	Jun. 30, 2020	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020	Dec. 31, 2018
Class of Stock [Line Items]
Dividends on common stock			$ 0		$ 0
Common stock, shares reserved for future issuance (in shares)			13,939,220		11,344,620
Issuance of common stock in public offering, net of offering costs (in shares)	4,312,500
Share price of stock issued (in usd per share)	$ 84	$ 84		$ 84
Issuance of common stock in public offering, net of offering costs	$ 354,600,000	$ 354,600,000		$ 354,600,000
Shares underlying outstanding stock options
Class of Stock [Line Items]
Common stock, shares reserved for future issuance (in shares)			2,703,906		3,101,181
Shares underlying unvested restricted stock units
Class of Stock [Line Items]
Common stock, shares reserved for future issuance (in shares)			1,155,370		1,118,655
Market-based restricted stock units
Class of Stock [Line Items]
Common stock, shares reserved for future issuance (in shares)			2,260,764		3,391,148
Performance-based restricted stock units
Class of Stock [Line Items]
Common stock, shares reserved for future issuance (in shares)			415,535		377,922
Shares available for issuance under the 2018 Incentive Award Plan
Class of Stock [Line Items]
Common stock, shares reserved for future issuance (in shares)			5,928,052		1,819,223
Shares available for issuance under the 2018 Employee Stock Purchase Plan
Class of Stock [Line Items]
Common stock, shares reserved for future issuance (in shares)			1,475,593		1,536,491	922,250

Stock-Based Compensation - Stoc

Stock-Based Compensation - Stock Option Activity (Details) $ / shares in Units, $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2021USD ($)$ / sharesshares	Dec. 31, 2020USD ($)$ / sharesshares
Shares Available for Grant
Beginning number of shares, available for grant (in shares)	1,819,223
2018 plan annual increase (in shares)	3,689,000
Ending number of shares, available for grant (in shares)	5,928,052	1,819,223
Shares Subject to Options Outstanding
Beginning number of shares, outstanding (in shares)	3,101,181
Granted (in shares)	60,677
Exercised (in shares)	(371,711)
Canceled (in shares)	(86,241)
Ending number of shares, outstanding (in shares)	2,703,906	3,101,181
Options vested and exercisable, number of options (in shares)	2,091,339
Weighted-Average Exercise Price
Beginning balance of options outstanding (in usd per share) | $ / shares	$ 15.80
Granted (in usd per share) | $ / shares	142.73
Exercised (in usd per share) | $ / shares	14.34
Canceled (in usd per share) | $ / shares	47.02
Ending balance of options outstanding (in usd per share) | $ / shares	17.86	$ 15.80
Options vested and exercisable, weighted average exercise price per share (in usd per share) | $ / shares	$ 9.16
Weighted-Average Remaining Contractual Life and Aggregate Intrinsic Value
Options outstanding, weighted average remaining contractual term (in years)	6 years 6 months	6 years 10 months 24 days
Options outstanding, aggregate intrinsic value | $	$ 288,749	$ 350,670
Options vested and exercisable, weighted average remaining contractual term (in years)	6 years 1 month 6 days
Options vested and exercisable, aggregate intrinsic value | $	$ 240,569
Equity Option
Shares Available for Grant
Granted (in shares)	(60,677)
Canceled (in shares)	42,956
Restricted Stock Units
Shares Available for Grant
Granted (in shares)	(177,166)
Canceled (in shares)	94,075
Market-based restricted stock units
Shares Available for Grant
Canceled (in shares)	558,254
Weighted-Average Remaining Contractual Life and Aggregate Intrinsic Value
Risky rate, cost of equity	0.16
Performance-based restricted stock units
Shares Available for Grant
Granted (in shares)	(52,917)
Canceled (in shares)	15,304

Stock-Based Compensation - Narr

Stock-Based Compensation - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands	May 26, 2020	Jan. 01, 2020	Nov. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average grant date fair value, grants in period (in usd per share)				$ 81.79	$ 44.61	$ 84.02	$ 45.52
Stock based compensation not recognized, options				$ 19,700		$ 19,700
Stock based compensation not recognized, period for recognition (years)						2 years 8 months 12 days
Stock-based compensation				$ 34,507	$ 25,815	$ 89,576	$ 32,153
Common stock, shares reserved for future issuance (in shares)				13,939,220		13,939,220		11,344,620
Class B | AMEA 2020 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average grant date fair value, grants in period (in usd per share)				$ 0.33		$ 0.33
Stock based compensation not recognized, options				$ 600		$ 600
Stock based compensation not recognized, period for recognition (years)						2 years 2 months 12 days
Total market-based restricted stock units approved and granted (in shares)						382,223
Guardant Health AMEA, Inc | Class B | AMEA 2020 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, shares reserved for future issuance (in shares)					4,595,555		4,595,555
Guardant Health AMEA, Inc | Class B | AMEA 2020 Plan | Tranche One
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Market-based stock unit vesting period						4 years
Option term, expiration period						10 years
Guardant Health AMEA, Inc | Class B | AMEA 2020 Plan | Tranche Two
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Option term, expiration period						5 years
Threshold percentage for individual's combined voting power triggering five year option term						10.00%
Purchase price of common stock (as a percent of the fair value of common stock)						110.00%
Stock options issued and outstanding
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercises in period, intrinsic value				$ 11,100	$ 33,100	$ 49,400	$ 50,300
Common stock, shares reserved for future issuance (in shares)				2,703,906		2,703,906		3,101,181
Expected dividend yield				0.00%	0.00%	0.00%	0.00%
Stock options issued and outstanding | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility				63.60%	66.50%	63.60%	66.50%
Risk-free interest rate				0.30%	0.40%	0.30%	0.40%
Stock options issued and outstanding | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility				66.70%	68.50%	66.70%	73.30%
Risk-free interest rate				1.10%	0.40%	1.10%	1.60%
Shares underlying unvested restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock based compensation not recognized, period for recognition (years)						3 years 1 month 6 days
Stock based compensation not recognized, other than options				$ 98,100		$ 98,100
Weighted average grant date fair value of MSU (in usd per share)						$ 154.94
Common stock, shares reserved for future issuance (in shares)				1,155,370		1,155,370		1,118,655
Performance-based restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock based compensation not recognized, period for recognition (years)						3 years 7 months 6 days
Stock based compensation not recognized, other than options				$ 4,900		$ 4,900
Additional service period requirement			6 months
Weighted-average derivative service period			4 years
Stock-based compensation				$ 300		$ 700
Total market-based restricted stock units approved and granted (in shares)						52,917
Weighted average grant date fair value of MSU (in usd per share)						$ 135.94
Common stock, shares reserved for future issuance (in shares)				415,535		415,535		377,922
Performance-based restricted stock units | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Market-based stock unit vesting period			4 years
Performance-based restricted stock units | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Market-based stock unit vesting period			4 years 6 months
MSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock based compensation not recognized, period for recognition (years)						9 months 18 days
Stock based compensation not recognized, other than options				$ 49,000		$ 49,000
Market-based stock unit vesting period	7 years
Stock-based compensation				$ 22,300		$ 66,300
Market-based restricted stock share price goal	30 days
Weighted average grant date fair value of MSU (in usd per share)						$ 67
Common stock, shares reserved for future issuance (in shares)				2,260,764		2,260,764		3,391,148
Expected dividend yield						0.00%
Expected volatility						65.50%
Risk-free interest rate						0.53%
Risky rate, cost of equity						0.16
MSUs | Chief Executive Officer
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total market-based restricted stock units approved and granted (in shares)	1,695,574
MSUs | President and Chief Operating Officer
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total market-based restricted stock units approved and granted (in shares)	1,695,574
MSUs | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average derivative service period						9 months 29 days
Market-based stock units holding period during vesting	6 months
Discount for post-vesting restrictions						10.40%
MSUs | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average derivative service period						2 years 25 days
Market-based stock units holding period during vesting	12 months
Discount for post-vesting restrictions						14.50%
Shares available for issuance under the 2018 Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock based compensation not recognized, period for recognition (years)						4 months 24 days
Stock based compensation not recognized, other than options				$ 1,400		$ 1,400
Stock-based compensation				$ 800	$ 1,100	$ 1,600	$ 1,600
Purchase price of common stock (as a percent of the fair value of common stock)						85.00%
Common stock, shares reserved for future issuance (in shares)				1,475,593		1,475,593		1,536,491	922,250
Expected dividend yield				0.00%	0.00%	0.00%	0.00%
Expected volatility				50.80%	73.20%	50.80%	73.20%
Risk-free interest rate				0.00%	0.20%	0.00%	0.20%
Shares authorized (in shares)		942,614
Maximum employee subscription rate, ESPP				10.00%		10.00%
Purchase period						6 months
Common stock issued under employee stock purchase plan (in shares)				60,898	58,164	60,898	58,164

Stock-Based Compensation - Rest

Stock-Based Compensation - Restricted Stock Activity (Details)	6 Months Ended
	Jun. 30, 2021$ / sharesshares
Shares underlying unvested restricted stock units
Restricted Stock Units Outstanding
Beginning unvested balance (in shares) | shares	1,118,655
Granted (in shares) | shares	177,166
Vested and released (in shares) | shares	(46,376)
Canceled (in shares) | shares	(94,075)
Ending unvested balance (in shares) | shares	1,155,370
Weighted-Average Grant Date Fair Value
Beginning balance of options outstanding (in usd per share)	$ 92.89
Granted (in usd per share)	154.94
Vested and released (in usd per share)	80.32
Canceled (in usd per share)	92.67
Ending balance of options outstanding (in usd per share)	$ 102.93
Performance-based restricted stock units
Restricted Stock Units Outstanding
Beginning unvested balance (in shares) | shares	377,922
Granted (in shares) | shares	52,917
Canceled (in shares) | shares	(15,304)
Ending unvested balance (in shares) | shares	415,535
Weighted-Average Grant Date Fair Value
Beginning balance of options outstanding (in usd per share)	$ 113.40
Granted (in usd per share)	135.94
Canceled (in usd per share)	113.40
Ending balance of options outstanding (in usd per share)	$ 116.27
MSUs
Restricted Stock Units Outstanding
Beginning unvested balance (in shares) | shares	3,391,148
Vested and released (in shares) | shares	(572,130)
Canceled (in shares) | shares	(558,254)
Ending unvested balance (in shares) | shares	2,260,764
Weighted-Average Grant Date Fair Value
Beginning balance of options outstanding (in usd per share)	$ 67
Granted (in usd per share)	67
Vested and released (in usd per share)	70.58
Canceled (in usd per share)	70.58
Ending balance of options outstanding (in usd per share)	$ 65.20

Stock-Based Compensation - Mark

Stock-Based Compensation - Market-based Restricted Stock Units (Details) - MSUs	6 Months Ended
	Jun. 30, 2021shares
Tranche 1 - $120 per share
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of MSUs (in shares)	565,192
Tranche 2 - $150 per share
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of MSUs (in shares)	565,191
Tranche 3 - $200 per share
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of MSUs (in shares)	565,191

Stock-Based Compensation - AMEA

Stock-Based Compensation - AMEA 2020 Equity Incentive Plan (Details) $ / shares in Units, $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2021USD ($)$ / sharesshares	Dec. 31, 2020USD ($)$ / sharesshares
Shares Available for Grant
Beginning number of shares, available for grant (in shares)	1,819,223
Ending number of shares, available for grant (in shares)	5,928,052	1,819,223
Shares Subject to Options Outstanding
Beginning number of shares, outstanding (in shares)	3,101,181
Granted (in shares)	60,677
Exercised (in shares)	(371,711)
Canceled (in shares)	(86,241)
Ending number of shares, outstanding (in shares)	2,703,906	3,101,181
Options vested and exercisable, number of options (in shares)	2,091,339
Weighted-Average Exercise Price
Beginning balance of options outstanding (in usd per share) | $ / shares	$ 15.80
Granted (in usd per share) | $ / shares	142.73
Exercised (in usd per share) | $ / shares	14.34
Canceled (in usd per share) | $ / shares	47.02
Ending balance of options outstanding (in usd per share) | $ / shares	17.86	$ 15.80
Options vested and exercisable, weighted average exercise price per share (in usd per share) | $ / shares	$ 9.16
Weighted-Average Remaining Contractual Life and Aggregate Intrinsic Value
Options outstanding, weighted average remaining contractual term (in years)	6 years 6 months	6 years 10 months 24 days
Options outstanding, aggregate intrinsic value | $	$ 288,749	$ 350,670
Options vested and exercisable, weighted average remaining contractual term (in years)	6 years 1 month 6 days
Options vested and exercisable, aggregate intrinsic value | $	$ 240,569
AMEA 2020 Plan | Class B
Shares Available for Grant
Beginning number of shares, available for grant (in shares)	542,220
Granted (in shares)	(382,223)
Canceled (in shares)	92,412
Ending number of shares, available for grant (in shares)	252,409	542,220
Shares Subject to Options Outstanding
Beginning number of shares, outstanding (in shares)	4,053,335
Granted (in shares)	382,223
Exercised (in shares)	(91,109)
Canceled (in shares)	(92,412)
Ending number of shares, outstanding (in shares)	4,252,037	4,053,335
Options vested and exercisable, number of options (in shares)	2,352,180
Weighted-Average Exercise Price
Beginning balance of options outstanding (in usd per share) | $ / shares	$ 0.58
Granted (in usd per share) | $ / shares	0.58
Exercised (in usd per share) | $ / shares	0.58
Canceled (in usd per share) | $ / shares	0.58
Ending balance of options outstanding (in usd per share) | $ / shares	0.58	$ 0.58
Options vested and exercisable, weighted average exercise price per share (in usd per share) | $ / shares	$ 0.58
Weighted-Average Remaining Contractual Life and Aggregate Intrinsic Value
Options outstanding, weighted average remaining contractual term (in years)	9 years 2 months 12 days	9 years 7 months 6 days
Options outstanding, aggregate intrinsic value | $	$ 0	$ 0
Options vested and exercisable, weighted average remaining contractual term (in years)	9 years 1 month 6 days
Options vested and exercisable, aggregate intrinsic value | $	$ 0

Stock-Based Compensation - St_2

Stock-Based Compensation - Stock Based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	$ 34,507	$ 25,815	$ 89,576	$ 32,153
Cost of precision oncology testing
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	873	407	1,640	710
Research and development expense
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	4,564	2,622	8,864	4,986
Sales and marketing expense
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	3,438	2,167	6,318	3,965
General and administrative expense
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	$ 25,632	$ 20,619	$ 72,754	$ 22,492

Stock-Based Compensation - Valu

Stock-Based Compensation - Valuation of Stock Options (Details) - Stock options issued and outstanding	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected dividend yield	0.00%	0.00%	0.00%	0.00%
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	5 years 5 months 26 days	5 years 6 months	5 years 5 months 26 days	5 years 6 months
Expected volatility	63.60%	66.50%	63.60%	66.50%
Risk-free interest rate	0.30%	0.40%	0.30%	0.40%
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	6 years 14 days	6 years 1 month 6 days	6 years 14 days	6 years 1 month 6 days
Expected volatility	66.70%	68.50%	66.70%	73.30%
Risk-free interest rate	1.10%	0.40%	1.10%	1.60%

Stock-Based Compensation - Empl

Stock-Based Compensation - Employee Stock Purchase Plan (Details) - Shares available for issuance under the 2018 Employee Stock Purchase Plan	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	6 months	6 months	6 months	6 months
Expected volatility	50.80%	73.20%	50.80%	73.20%
Risk-free interest rate	0.00%	0.20%	0.00%	0.20%
Expected dividend yield	0.00%	0.00%	0.00%	0.00%

Net Loss Per Share Attributab_3

Net Loss Per Share Attributable to Guardant Health, Inc. Common Stockholders - Schedule of Net Loss Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Earnings Per Share [Abstract]
Net loss	$ (97,575)	$ (49,739)	$ (204,933)	$ (81,568)
Adjustment of redeemable noncontrolling interest	0	(4,900)	(2,300)	(800)
Net loss attributable to Guardant Health, Inc. common stockholders, basic	(97,575)	(54,639)	(207,233)	(82,368)
Net loss attributable to Guardant Health, Inc. common stockholders	$ (97,575)	$ (54,639)	$ (207,233)	$ (82,368)
Net loss per share attributable to Guardant Health, Inc. common stockholders, basic (in usd per share)	$ (0.96)	$ (0.57)	$ (2.05)	$ (0.87)
Net loss per share attributable to Guardant Health, Inc. common stockholders, diluted (in usd per share)	$ (0.96)	$ (0.57)	$ (2.05)	$ (0.87)
Weighted-average shares used in computing net loss per share attributable to Guardant Health, Inc. common stockholders, basic (in shares)	101,172	96,011	101,064	95,196
Weighted-average shares used in computing net loss per share attributable to Guardant Health, Inc. common stockholders, diluted (in shares)	101,172	96,011	101,064	95,196

Net Loss Per Share Attributab_4

Net Loss Per Share Attributable to Guardant Health, Inc. Common Stockholders - Schedule of Antidilutive Securities (Details) - shares	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	14,813,000	5,997,000	15,090,000	5,451,000
Stock options outstanding (in shares)	2,703,906		2,703,906		3,101,181
AMEA 2020 Plan | Class B
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Stock options outstanding (in shares)	4,252,037		4,252,037		4,053,335
Stock options issued and outstanding
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	2,720,000	4,056,000	2,816,000	4,200,000
Restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	1,147,000	542,000	1,133,000	519,000
MSUs
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	2,261,000	1,342,000	2,453,000	671,000
PSUs
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	409,000	0	408,000	0
ESPP obligation
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	43,000	37,000	45,000	40,000
Common stock subject to repurchase
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	8,000	20,000	10,000	21,000
Convertible senior notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	8,225,000	0	8,225,000	0

Segment and Geographic Inform_3

Segment and Geographic Information (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Segment Reporting Information [Line Items]
Total revenue	$ 92,101	$ 66,335	$ 170,766	$ 133,845
Assets | Geographic Concentration Risk | Net Assets, Geographic Area
Segment Reporting Information [Line Items]
Concentration risk, percentage			98.00%		94.00%
United States
Segment Reporting Information [Line Items]
Total revenue	87,868	61,422	$ 160,168	126,035
International
Segment Reporting Information [Line Items]
Total revenue	$ 4,233	$ 4,913	$ 10,598	$ 7,810

Subsequent Events (Details)

Subsequent Events (Details) - USD ($) $ in Thousands	1 Months Ended	6 Months Ended
	Jul. 31, 2021	Jun. 30, 2021	Jun. 30, 2020
Subsequent Event [Line Items]
Non-marketable equity and other investments		$ 12,750	$ 0
Subsequent Event
Subsequent Event [Line Items]
Non-marketable equity and other investments	$ 26,000