Related Party Transactions	3 Months Ended
Related Party Transactions	Mar. 31, 2020
Related Party Transactions [Abstract]
Related Party Transactions	Related Party Transactions As of March 31, 2020, Pfizer held 22,032,040 shares of Common Stock and had appointed one member to the Company’s board of directors. In April 2018, the Company and Pfizer entered into a transition services agreement (the Pfizer TSA) for Pfizer to provide professional services to the Company related to research and development, project management, and other administrative functions. In September 2019, the Company and Pfizer terminated the Pfizer TSA. For the three months ended March 31, 2020 and 2019, the costs incurred under the Pfizer TSA were zero and $2.7 million, respectively. The Company also purchased certain lab supplies from Pfizer in connection with its research and development activities. For the three months ended March 31, 2020 and 2019, the total lab supplies and services purchased from Pfizer were zero and $0.6, million respectively. As of March 31, 2020 and December 31, 2019, the Company had an amount payable to Pfizer of zero and $1.7 million, respectively, which was recorded in the accrued and other current liabilities on the accompanying condensed balance sheets. Sublease Agreement In December 2018, the Company entered into a sublease with Bellco Capital LLC (Bellco) for 1,293 square feet of office space in Los Angeles California for a three year term. The Company’s executive chairman, Arie Belldegrun, M.D., FACS, is the Chairman and an owner of Bellco. The total right of use asset and associated liability recorded related to this related party lease was $0.1 million and $0.2 million at March 31, 2020 and 2019, respectively. In February 2019, the Company subleased 2,180 square feet of its office space in New York, New York, to ByHeart, Inc.(ByHeart), formerly known as Second Science, Inc. ByHeart is a development-stage infant formula company. Certain of the Company’s board members and executive officers have beneficial ownership in ByHeart and two serve on the board of directors of ByHeart. In September 2019, the Company entered into an amendment to the sublease agreement and increased the subleased space to 2,907 square feet. Sublease income for the three months ended March 31, 2020 and 2019 was $0.1 million and was recognized as other income. Consulting Agreements In June 2018, the Company entered into a services agreement with Two River Consulting LLC (Two River) a firm affiliated with the Company’s President and Chief Executive Officer, the Company’s Executive Chairman of the board of directors, and a director of the Company to provide various managerial, administrative, accounting and financial services to the Company. The costs incurred for services provided under this agreement were $0.1 million and $0.2 million for the three months ended March 31, 2020 and 2019, respectively. In August 2018, the Company entered into a consulting agreement with Bellco. Pursuant to the consulting agreement, Bellco provides certain services for the Company, which are performed by Dr. Belldegrun and include without limitation, providing advice and analysis with respect to the Company’s business, business strategy and potential opportunities in the field of allogeneic CAR T cell therapy and any other aspect of the CAR T cell therapy business as the Company may agree. In consideration for these services, the Company paid Bellco $33,333 per month in arrears commencing January 2019 and $37,500 per month in arrears commencing January 2020. The Company may also, at its discretion, pay Bellco an annual performance award in an amount up to 60% of the aggregate compensation payable to Bellco in a calendar year. The Company also reimburses Bellco for out of pocket expenses incurred in performing the services. The cost incurred for services provided and out-of-pocket expenses incurred under this consulting agreement were $0.2 million for the three months ended March 31, 2020 and 2019, respectively