Condensed Consolidated Statements of Comprehensive Loss (unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Statement of Comprehensive Income [Abstract]
Net loss	$ (31,829)	$ (21,351)
Other comprehensive income, net of tax impact:
Unrealized gain on available-for-sale securities	6,571	485
Foreign currency translation adjustments	23	(69)
Other comprehensive income	6,594	416
Comprehensive loss	(25,235)	(20,935)
Comprehensive gain (loss) attributable to redeemable noncontrolling interest	4,100	(4,700)
Comprehensive loss attributable to Guardant Health, Inc.	$ (21,135)	$ (25,635)