Condensed Consolidated Statements of Operations (unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Revenue:
Precision oncology testing	$ 50,991	$ 42,064	$ 111,237	$ 70,901
Development services	15,344	11,911	22,608	19,729
Total revenue	66,335	53,975	133,845	90,630
Costs and operating expenses:
Cost of precision oncology testing	17,809	14,650	36,000	25,673
Cost of development services	4,626	2,183	6,941	4,695
Research and development expense	36,319	19,532	73,335	35,848
Sales and marketing expense	25,015	19,439	50,130	37,246
General and administrative expense	37,186	13,439	56,971	26,100
Total costs and operating expenses	120,955	69,243	223,377	129,562
Loss from operations	(54,620)	(15,268)	(89,532)	(38,932)
Interest income	2,640	3,099	5,958	5,584
Interest expense	(10)	(287)	(22)	(580)
Other income (expense), net	2,285	(51)	2,076	96
Loss before provision for income taxes	(49,705)	(12,507)	(81,520)	(33,832)
Provision for (benefit from) income taxes	34	(1,207)	48	(1,181)
Net loss	(49,739)	(11,300)	(81,568)	(32,651)
Adjustment of redeemable noncontrolling interest	(4,900)	(300)	(800)	(5,000)
Net loss attributable to Guardant Health, Inc. common stockholders	$ (54,639)	$ (11,600)	$ (82,368)	$ (37,651)
Net loss per share attributable to Guardant Health, Inc. common stockholders, basic and diluted (in usd per share)	$ (0.57)	$ (0.13)	$ (0.87)	$ (0.43)
Weighted-average shares used in computing net loss per share attributable to Guardant Health, Inc. common stockholders, basic and diluted (in shares)	96,011	89,036	95,196	87,494