Condensed Consolidated Statements of Operations (unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Revenue:
Precision oncology testing	$ 52,147	$ 18,298	$ 123,048	$ 50,311
Development services	8,701	3,394	28,430	7,455
Total revenue	60,848	21,692	151,478	57,766
Costs and operating expenses:
Cost of precision oncology testing	16,578	9,671	42,251	27,222
Cost of development services	1,936	380	6,631	2,041
Research and development expense	24,569	14,253	60,417	34,062
Sales and marketing expense	18,802	13,464	56,048	36,351
General and administrative expense	16,440	8,129	42,540	23,645
Total costs and operating expenses	78,325	45,897	207,887	123,321
Loss from operations	(17,477)	(24,205)	(56,409)	(65,555)
Interest income	4,286	958	9,870	2,932
Interest expense	(280)	(304)	(860)	(952)
Other income (expense), net	179	43	275	4,587
Loss before provision for (benefit from) income taxes	(13,292)	(23,508)	(47,124)	(58,988)
Provision for (benefit from) income taxes	(202)	0	(1,383)	3
Net loss	(13,090)	(23,508)	(45,741)	(58,991)
Fair value adjustment of redeemable noncontrolling interest	300	(950)	(4,700)	(950)
Net loss attributable to Guardant Health, Inc. common stockholders	$ (12,790)	$ (24,458)	$ (50,441)	$ (59,941)
Net loss per share attributable to common stockholders, basic and diluted (in usd per share)	$ (0.14)	$ (1.94)	$ (0.56)	$ (4.87)
Weighted-average shares used in computing net loss per share attributable to common stockholders, basic and diluted (in shares)	93,303	12,582	89,452	12,300