Subsequent Events	6 Months Ended
Jun. 30, 2020
Subsequent Events [Abstract]
Subsequent Events	Note 11. Subsequent Events On May 27, 2020, the Company entered into an Option, License and Collaboration Agreement (Gilead Collaboration Agreement), Common Stock Purchase Agreement (the Purchase Agreement), and Investor Rights Agreement, each with Gilead Sciences, Inc. (Gilead). The transaction closed on July 13, 2020 following expiration of the antitrust waiting period. Upon closing, Gilead made an upfront payment of $175 million pursuant to the Gilead Collaboration Agreement, Gilead made an equity investment of approximately $200 million in the Company by purchasing 5,963,029 shares of Arcus common stock at a per share price of $33.54 pursuant to the Purchase Agreement, and the Company appointed Gilead’s designee, Merdad Parsey, M.D., Ph.D., to the Company’s Board of Directors pursuant to the Investor Rights Agreement. Pursuant to the terms of the Gilead Collaboration Agreement, Gilead has an exclusive license to develop and commercialize zimberelimab (formerly referred to as AB122) in certain markets and obtained exclusive options to acquire an exclusive license to develop and commercialize all of the Company’s current and future clinical programs during the 10-year collaboration term and, for those programs that enter clinical development prior to the end of the collaboration term, for up to an additional three years thereafter. Gilead may exercise its option, on a program-by-program basis, upon payment of an option fee that ranges from $200 million to $275 million per program for the Company’s current clinical programs, and $150 million per program for all other programs that enter clinical development. If Gilead exercises its option with respect to the Company’s TIGIT program, the Company is also eligible to receive up to $500 million in potential U.S. regulatory approval milestones with respect to domvanalimab (formerly referred to as AB154). Upon Gilead’s exercise of its option to a program, the two companies will co-develop and equally share global development costs, subject to certain opt-out rights of the Company, expense caps on the Company’s spending and true-up adjustments. For each optioned program, provided the Company has not exercised its opt-out rights, the Company has an option to co-promote in the United States with equal sharing of related profits and losses. Gilead has the right to exclusively commercialize any optioned programs outside of the U.S., subject to the rights of the Company’s existing partners to any territories, and Gilead will pay to the Company tiered royalties as a percentage of revenues ranging from the high teens to the low twenties. Gilead will further provide ongoing research and development support of up to $400 million over the collaboration term. Pursuant to the Purchase Agreement and the Investor Rights Agreement, Gilead has the right, at its option, to purchase additional shares from the Company, up to a maximum of 35% of the Company’s then-outstanding voting common stock, from time to time over the next five years, at a purchase price equal to the greater of a 20% premium to market (based on a trailing five-day average closing price) at the time Gilead exercises such option, and the $33.54 initial purchase price. The Investor Rights Agreement also includes a three-year standstill and a two-year lockup and provides Gilead with registration rights commencing at the end of the lockup period, pro rata participation rights in certain future financings and the right to designate two individuals to be appointed to the Company’s Board of Directors.

Subsequent Events

6 Months Ended

Jun. 30, 2020

Note 11. Subsequent Events

On May 27, 2020, the Company entered into an Option, License and Collaboration Agreement (Gilead Collaboration Agreement), Common Stock Purchase Agreement (the Purchase Agreement), and Investor Rights Agreement, each with Gilead Sciences, Inc. (Gilead). The transaction closed on July 13, 2020 following expiration of the antitrust waiting period. Upon closing, Gilead made an upfront payment of $175 million pursuant to the Gilead Collaboration Agreement, Gilead made an equity investment of approximately $200 million in the Company by purchasing 5,963,029 shares of Arcus common stock at a per share price of $33.54 pursuant to the Purchase Agreement, and the Company appointed Gilead’s designee, Merdad Parsey, M.D., Ph.D., to the Company’s Board of Directors pursuant to the Investor Rights Agreement.

Pursuant to the terms of the Gilead Collaboration Agreement, Gilead has an exclusive license to develop and commercialize zimberelimab (formerly referred to as AB122) in certain markets and obtained exclusive options to acquire an exclusive license to develop and commercialize all of the Company’s current and future clinical programs during the 10-year collaboration term and, for those programs that enter clinical development prior to the end of the collaboration term, for up to an additional three years thereafter. Gilead may exercise its option, on a program-by-program basis, upon payment of an option fee that ranges from $200 million to $275 million per program for the Company’s current clinical programs, and $150 million per program for all other programs that enter clinical development. If Gilead exercises its option with respect to the Company’s TIGIT program, the Company is also eligible to receive up to $500 million in potential U.S. regulatory approval milestones with respect to domvanalimab (formerly referred to as AB154).

Upon Gilead’s exercise of its option to a program, the two companies will co-develop and equally share global development costs, subject to certain opt-out rights of the Company, expense caps on the Company’s spending and true-up adjustments. For each optioned program, provided the Company has not exercised its opt-out rights, the Company has an option to co-promote in the United States with equal sharing of related profits and losses. Gilead has the right to exclusively commercialize any optioned programs outside of the U.S., subject to the rights of the Company’s existing partners to any territories, and Gilead will pay to the Company tiered royalties as a percentage of revenues ranging from the high teens to the low twenties. Gilead will further provide ongoing research and development support of up to $400 million over the collaboration term.

Pursuant to the Purchase Agreement and the Investor Rights Agreement, Gilead has the right, at its option, to purchase additional shares from the Company, up to a maximum of 35% of the Company’s then-outstanding voting common stock, from time to time over the next five years, at a purchase price equal to the greater of a 20% premium to market (based on a trailing five-day average closing price) at the time Gilead exercises such option, and the $33.54 initial purchase price. The Investor Rights Agreement also includes a three-year standstill and a two-year lockup and provides Gilead with registration rights commencing at the end of the lockup period, pro rata participation rights in certain future financings and the right to designate two individuals to be appointed to the Company’s Board of Directors.