Commitments and Contingencies - Narrative (Details)	1 Months Ended
	Jul. 31, 2018 petition patent	Mar. 31, 2018 petition	Nov. 30, 2017 company patent
Other Commitments [Line Items]
Gain contingency, patents allegedly infringed upon, number | patent	4		4
Personal Genome Diagnostics, Inc. and Foundation Medicine, Inc, vs. Guardant Health, Inc. Subsequent Filing
Other Commitments [Line Items]
Number of companies that infringed on a patent | company			2
Personal Genome Diagnostics, Inc. vs. Guardant Health, Inc.
Other Commitments [Line Items]
Number of petitions filed	2	2
Personal Genome Diagnostics, Inc. vs. Guardant Health, Inc. Subsequent Filing
Other Commitments [Line Items]
Number of petitions filed	6
Number of petitions denied	4