License and Collaboration Agreements (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Deferred revenue, current	$ 23,688,000		$ 23,688,000		$ 1,435,000
Product | AbbVie
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Remaining balance in deferred revenue	59,900,000		59,900,000
Potential cash payment upon excercising license option	75,000,000.0		75,000,000.0
Potential cash payment upon achievement of certain development and commercial milestones	205,000,000.0		205,000,000.0
Potential cash payment upon achievement of certain sales-based cash milestones	450,000,000.0		450,000,000.0
Revenue	86,000		86,000
Product | AbbVie | Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Potential future milestones receivable (up to)	75,000,000.0		75,000,000.0
Product | AbbVie | Upfront License Payment
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Remaining balance in deferred revenue	60,000,000.0		60,000,000.0
Product | Adaptimmune
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Revenue	602,000	$ 142,000	1,700,000	$ 142,000
Deferred revenue, current	242,000		242,000
Product | Adaptimmune | Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Potential future milestones receivable (up to)	288,000,000.0		288,000,000.0
Product | Adaptimmune | Upfront License Payment
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Remaining balance in deferred revenue		$ 2,000,000.0		$ 2,000,000.0
Product | Adaptimmune | Research Support Payment
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Remaining balance in deferred revenue	$ 1,300,000		$ 1,300,000