Agreements - Fusion (Details) - USD ($)	3 Months Ended														6 Months Ended		12 Months Ended
	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, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jun. 30, 2016
Collaborative Agreements disclosures
Revenue from contract with customer	$ 13,416,000	$ 10,928,000	$ 9,287,000	$ 19,815,000	$ 39,448,000	$ 8,480,000	$ 39,020,000	$ 28,499,000	$ 13,846,000	$ 7,660,000	$ 7,408,000	$ 19,714,000	$ 18,029,000	$ 14,851,000	$ 21,506,000	$ 32,880,000	$ 53,446,000	$ 115,447,000	$ 48,628,000	$ 60,002,000
Fusion Pharmaceuticals
Collaborative Agreements disclosures
Potential milestone payment	500,000																500,000
Fusion Pharmaceuticals | Development milestones
Collaborative Agreements disclosures
Potential milestone payment									15,000,000						15,000,000				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						35,000,000				35,000,000
ASU 2014-09 | Adjustments due to new guidance
Collaborative Agreements disclosures
Revenue from contract with customer																	5,000,000
License and milestone fees
Collaborative Agreements disclosures
Revenue from contract with customer	1,747,000	672,000	1,321,000	11,540,000	29,580,000	79,000	31,080,000	18,730,000	5,076,000	76,000	76,000	10,077,000	10,692,000	6,070,000	5,152,000	16,762,000	15,280,000	79,469,000	15,305,000	26,915,000
License and milestone fees | Fusion Pharmaceuticals
Collaborative Agreements disclosures
Potential milestone payment									50,000,000						50,000,000				50,000,000
License and milestone fees | Fusion Pharmaceuticals | Phase 1 clinical trial
Collaborative Agreements disclosures
Revenue from contract with customer																	500,000
License and milestone fees | ASU 2014-09 | Adjustments due to new guidance
Collaborative Agreements disclosures
Potential milestone payment	5,000,000																5,000,000
Research and development support
Collaborative Agreements disclosures
Revenue from contract with customer	218,000	388,000	388,000	383,000	452,000	650,000	902,000	1,478,000	1,427,000	1,354,000	1,335,000	1,059,000	848,000	772,000	2,781,000	1,620,000	1,377,000	3,482,000	5,175,000	4,014,000
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	$ 633,000	$ 46,000	$ 53,000	$ 1,198,000	$ 3,000	$ 2,325,000	$ 679,000	$ 2,328,000	$ 4,635,000	$ 4,354,000	$ 1,930,000	$ 3,579,000