Description of Business	6 Months Ended
	Jun. 30, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Description of Business	Description of BusinessGuardant Health, Inc. (the “Company”) is a leading precision oncology company focused on helping conquer cancer globally through use of its proprietary blood tests, vast data sets and advanced analytics. The key to conquering cancer is unprecedented access to its molecular information throughout all stages of the disease, which the Company enables by a routine blood draw, or liquid biopsy. The Guardant Health Oncology Platform is designed to leverage the Company’s capabilities in technology, clinical development, regulatory and reimbursement to drive commercial adoption, accelerate drug development, improve patient clinical outcomes and lower healthcare costs. In pursuit of its goal to manage cancer across all stages of the disease, the Company has launched its Guardant360 and GuardantOMNI liquid biopsy-based tests for advanced stage cancer and is developing tests from its LUNAR program which aims to address the needs of early stage cancer patients with neoadjuvant and adjuvant treatment selection, cancer survivors with surveillance, and asymptomatic individuals eligible for cancer screening and individuals at a higher risk for developing cancer with early detection and is developing tests from its LUNAR program which aims to address the needs of early stage cancer patients with neoadjuvant and adjuvant treatment selection, cancer survivors with surveillance, and asymptomatic individuals eligible for cancer screening and individuals at a higher risk for developing cancer with early detection. Using data collected from the Company's Guardant360 tests, the Company has also developed GuardantINFORM platform to further accelerate precision oncology drug development by biopharmaceutical companies by offering them an in-silico research platform to further unlock insights into tumor evolution and treatment resistance across various biomarker-driven cancers. The Company was incorporated in Delaware in December 2011 and is headquartered in Redwood City, California. In May 2018, the Company formed and capitalized Guardant Health AMEA, Inc. (the “Joint Venture”) in the United States with an affiliate of SoftBank Vision Fund (AIV M1) L.P. (“SoftBank”). Under the terms of the joint venture agreement, the Company held a 50% ownership interest in the Joint Venture. As of June 30, 2020, the Joint Venture has subsidiaries in Singapore and Japan (see Note 3, Investment in Joint Venture) and the Company has a subsidiary in Switzerland, which was incorporated in 2019.