Net Loss Per Share Attributable to Guardant Health, Inc. Common Stockholders - Schedule of Net Loss Per Share Attributable to Common Stockholders (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Earnings Per Share [Abstract]
Net loss	$ (479,449)	$ (654,588)	$ (384,770)
Adjustment of redeemable noncontrolling interest	0	0	(20,900)
Net loss attributable to Guardant Health, Inc. common stockholders - basic	(479,449)	(654,588)	(405,670)
Net loss attributable to Guardant Health, Inc. common stockholders - diluted	$ (479,449)	$ (654,588)	$ (405,670)
Net loss per share attributable to Guardant Health, Inc. common stockholders, basic (in usd per share)	$ (4.28)	$ (6.41)	$ (4.00)
Net loss per share attributable to Guardant Health, Inc. common stockholders, diluted (in usd per share)	$ (4.28)	$ (6.41)	$ (4.00)
Weighted-average shares used in computing net loss per share attributable to Guardant Health, Inc. common stockholders, basic (in shares)	111,988	102,178	101,314
Weighted-average shares used in computing net loss per share attributable to Guardant Health, Inc. common stockholders, diluted (in shares)	111,988	102,178	101,314