Description of Business	3 Months Ended
Mar. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Description of Business	Description of Business Guardant 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 it 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, reimbursement and commercial adoption to improve patient clinical outcomes, lower healthcare costs and accelerate biopharmaceutical drug development. In pursuit of its goal to manage cancer across all stages of the disease, it has launched its Guardant360 and GuardantOMNI liquid biopsy-based tests for advanced stage cancer patients, and is developing tests from its LUNAR early detection program to address the needs of early stage cancer patients with adjuvant treatment selection, cancer survivors with surveillance and asymptomatic individuals with screening. The Company was incorporated in Delaware in December 2011 and is headquartered in Redwood City, California. In April 2018, the Company established Guardant Health AMEA, Inc. (the “Joint Venture”) in the United States with an entity affiliated with SoftBank. Under the terms of the joint venture agreement, the Company held a 50% ownership interest in the Joint Venture. As of March 31, 2019, the Joint Venture has subsidiaries in Singapore and Japan (see Note 3). Reverse Stock Split In September 2018, the Company’s Board of Directors and its stockholders approved a 0.7378-for-one reverse stock split of the Company’s common stock. The reverse stock split became effective on September 19, 2018. The par value of the common stock was not adjusted as a result of the reverse stock split. Adjustments corresponding to the reverse stock split were made to the ratio at which the convertible preferred stock was convertible into common stock immediately prior to the closing of the Company's initial public offering (the “IPO”). All share and per share amounts in the accompanying condensed consolidated financial statements have been retroactively adjusted for all periods presented to give effect to this reverse stock split.

Description of Business

Guardant 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 it 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, reimbursement and commercial adoption to improve patient clinical outcomes, lower healthcare costs and accelerate biopharmaceutical drug development. In pursuit of its goal to manage cancer across all stages of the disease, it has launched its Guardant360 and GuardantOMNI liquid biopsy-based tests for advanced stage cancer patients, and is developing tests from its LUNAR early detection program to address the needs of early stage cancer patients with adjuvant treatment selection, cancer survivors with surveillance and asymptomatic individuals with screening.

The Company was incorporated in Delaware in December 2011 and is headquartered in Redwood City, California. In April 2018, the Company established Guardant Health AMEA, Inc. (the “Joint Venture”) in the United States with an entity affiliated with SoftBank. Under the terms of the joint venture agreement, the Company held a 50% ownership interest in the Joint Venture. As of March 31, 2019, the Joint Venture has subsidiaries in Singapore and Japan (see Note 3).

Reverse Stock Split

In September 2018, the Company’s Board of Directors and its stockholders approved a 0.7378-for-one reverse stock split of the Company’s common stock. The reverse stock split became effective on September 19, 2018. The par value of the common stock was not adjusted as a result of the reverse stock split. Adjustments corresponding to the reverse stock split were made to the ratio at which the convertible preferred stock was convertible into common stock immediately prior to the closing of the Company's initial public offering (the “IPO”). All share and per share amounts in the accompanying condensed consolidated financial statements have been retroactively adjusted for all periods presented to give effect to this reverse stock split.