Condensed Consolidated Statements of Operations (unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Revenue:
Precision oncology testing	$ 42,064	$ 17,822	$ 70,901	$ 32,013
Development services	11,911	1,560	19,729	4,061
Total revenue	53,975	19,382	90,630	36,074
Costs and operating expenses:
Cost of precision oncology testing	14,650	9,506	25,673	17,551
Cost of development services	2,183	453	4,695	1,661
Research and development expense	19,532	11,554	35,848	19,809
Sales and marketing expense	19,439	11,575	37,246	22,887
General and administrative expense	13,439	8,997	26,100	15,516
Total costs and operating expenses	69,243	42,085	129,562	77,424
Loss from operations	(15,268)	(22,703)	(38,932)	(41,350)
Interest income	3,099	989	5,584	1,974
Interest expense	(287)	(317)	(580)	(648)
Other income (expense), net	(51)	395	96	4,544
Loss before provision for income taxes	(12,507)	(21,636)	(33,832)	(35,480)
Provision for (benefit from) income taxes	(1,207)	3	(1,181)	3
Net loss	(11,300)	(21,639)	(32,651)	(35,483)
Fair value adjustment of redeemable noncontrolling interest	(300)	0	(5,000)	0
Net loss attributable to Guardant Health, Inc. common stockholders	$ (11,600)	$ (21,639)	$ (37,651)	$ (35,483)
Net loss per share attributable to common stockholders, basic and diluted (in usd per share)	$ (0.13)	$ (1.75)	$ (0.43)	$ (2.92)
Weighted-average shares used in computing net loss per share attributable to common stockholders, basic and diluted (in shares)	89,036	12,388	87,494	12,155