License and Collaboration Agreements (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Deferred revenue, current	$ 28,505,000		$ 28,505,000			$ 1,435,000
Product | AbbVie
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Contract with customer, liability	58,400,000		58,400,000
Potential cash payment upon excercising license option					$ 75,000,000.0
Potential cash payment upon achievement of certain development and commercial milestones					205,000,000.0
Potential cash payment upon achievement of certain sales-based cash milestones					450,000,000.0
Revenue	1,600,000		1,600,000
Product | AbbVie | Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Potential future milestones receivable (up to)					75,000,000.0
Product | AbbVie | Upfront License Payment
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Contract with customer, liability					$ 60,000,000.0
Product | Adaptimmune
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Revenue	356,000	$ 288,000	2,000,000.0	$ 431,000
Deferred revenue, current	136,000		136,000
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]
Contract with customer, liability							$ 2,000,000.0
Product | Adaptimmune | Research Support Payment
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Contract with customer, liability	$ 1,300,000		$ 1,300,000