Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Statement of Comprehensive Income [Abstract]
Net loss	$ (67,851)	$ (84,263)	$ (83,221)
Other comprehensive income (loss), net of tax impact:
Unrealized gain (loss) on available-for-sale securities	1,110	449	(446)
Foreign currency translation adjustments	84	0	0
Other comprehensive income (loss)	1,194	449	(446)
Comprehensive loss	(66,657)	(83,814)	(83,667)
Comprehensive loss attributable to redeemable noncontrolling interest	(7,800)	(800)	0
Comprehensive loss attributable to Guardant Health, Inc.	$ (74,457)	$ (84,614)	$ (83,667)