Condensed Consolidated Statements of Comprehensive Loss (unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Statement of Comprehensive Income [Abstract]
Net loss	$ (49,739)	$ (11,300)	$ (81,568)	$ (32,651)
Other comprehensive income (loss), net of tax impact:
Unrealized gain (loss) on available-for-sale securities	(2,338)	852	4,233	1,337
Foreign currency translation adjustments	25	159	48	90
Other comprehensive income (loss)	(2,313)	1,011	4,281	1,427
Comprehensive loss	(52,052)	(10,289)	(77,287)	(31,224)
Comprehensive loss attributable to redeemable noncontrolling interest	(4,900)	(300)	(800)	(5,000)
Comprehensive loss attributable to Guardant Health, Inc.	$ (56,952)	$ (10,589)	$ (78,087)	$ (36,224)