Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenue:
Precision oncology testing	[1]	$ 180,462	$ 78,407	$ 42,088
Development services	[1]	33,913	12,232	7,754
Total revenue		214,375	90,639	49,842
Costs and operating expenses:
Cost of precision oncology testing		62,255	39,846	28,883
Cost of development services		8,465	3,364	2,735
Research and development expense		86,292	50,714	25,562
Sales and marketing expense		78,335	53,465	32,497
General and administrative expense		61,399	36,192	36,777
Total costs and operating expenses		296,746	183,581	126,454
Loss from operations		(82,371)	(92,942)	(76,612)
Interest income		13,741	5,266	2,234
Interest expense		(1,181)	(1,251)	(2,702)
Loss on debt extinguishment		0	0	(5,075)
Other income (expense), net		88	4,702	(1,059)
Loss before provision for income taxes		(69,723)	(84,225)	(83,214)
Provision for (benefit from) income taxes		(1,872)	38	7
Net loss		(67,851)	(84,263)	(83,221)
Adjustment of redeemable noncontrolling interest		(7,800)	(800)	0
Net loss attributable to Guardant Health, Inc.		(75,651)	(85,063)	(83,221)
Deemed dividend related to repurchase of convertible preferred stock		(1,100)
Net loss attributable to Guardant Health, Inc. common stockholders		$ (75,651)	$ (85,063)	$ (88,995)
Net loss per share attributable to common stockholders, basic and diluted (in usd per share)		$ (0.84)	$ (2.80)	$ (7.07)
Weighted-average shares used in computing net loss per share attributable to common stockholders, basic and diluted (in shares)		90,597	30,403	12,582
Series A Convertible Preferred Stock
Costs and operating expenses:
Deemed dividend related to repurchase of convertible preferred stock		$ 0	$ 0	$ (4,716)
Series D Convertible Preferred Stock
Costs and operating expenses:
Deemed dividend related to repurchase of convertible preferred stock		$ 0	$ 0	$ (1,058)

[1] Fiscal year 2018 and 2017 results do not reflect the impact of the adoption of the new revenue accounting standard in fiscal year 2019.