Agreements - Fusion (Details) - USD ($)	3 Months Ended												12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Collaborative Agreements disclosures
Revenue from contract with customer	$ 44,864,000	$ 13,281,000	$ 15,542,000	$ 8,584,000	$ 13,416,000	$ 10,928,000	$ 9,287,000	$ 19,815,000	$ 39,448,000	$ 8,480,000	$ 39,020,000	$ 28,499,000	$ 82,271,000	$ 53,446,000	$ 115,447,000
Fusion Pharmaceuticals | Development milestones
Collaborative Agreements disclosures
Potential milestone payment																$ 15,000,000
Fusion Pharmaceuticals | Phase 2 clinical trial
Collaborative Agreements disclosures
Potential milestone payment					1,500,000									1,500,000
Fusion Pharmaceuticals | Milestone payments
Collaborative Agreements disclosures
Potential milestone payment																35,000,000
License and milestone fees
Collaborative Agreements disclosures
Revenue from contract with customer	$ 29,551,000	$ 79,000	5,079,000	79,000	1,747,000	672,000	1,321,000	11,540,000	29,580,000	79,000	31,080,000	18,730,000	34,788,000	15,280,000	79,469,000
License and milestone fees | Fusion Pharmaceuticals
Collaborative Agreements disclosures
Potential milestone payment																$ 50,000,000
License and milestone fees | Fusion Pharmaceuticals | Phase 1 clinical trial
Collaborative Agreements disclosures
Revenue from contract with customer														500,000
Research and development support
Collaborative Agreements disclosures
Revenue from contract with customer			$ 51,000	$ 17,000	218,000	388,000	388,000	383,000	452,000	650,000	902,000	1,478,000	$ 68,000	1,377,000	3,482,000
Clinical materials revenue
Collaborative Agreements disclosures
Revenue from contract with customer					$ 2,170,000	$ 1,427,000	$ 336,000	$ 702,000	$ 1,829,000	$ 1,248,000	$ 599,000	$ 678,000		$ 4,635,000	$ 4,354,000