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License agreements - Lilly (Details) - USD ($) $ in Thousands	1 Months Ended				3 Months Ended								12 Months Ended			121 Months Ended
	May 31, 2019	Mar. 31, 2016	Jul. 31, 2010	Dec. 31, 2009	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, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2019
License agreements
Research and Development Expense													$ 1,154,111	$ 1,197,957	$ 1,326,134
Revenues					$ 579,389	$ 551,581	$ 529,932	$ 497,857	$ 528,402	$ 449,683	$ 521,516	$ 382,282	2,158,759	1,881,883	1,536,216
Europe
License agreements
Revenues													90,000	79,900	66,900
Eli Lilly
License agreements
Upfront payment received under license agreement				$ 90,000
Revenues													0	120,000	110,000
Product royalties in accounts receivable					$ 23,600				14,000				23,600	14,000		$ 23,600
Eli Lilly \| Non-U.S.
License agreements
Revenues													$ 80,400	40,100	9,100
Eli Lilly \| Phase IIB
License agreements
Associated future global development costs from the initiation of a Phase IIb trial, if elected to co-develop (as a percentage)			30.00%	30.00%									30.00%
Research and Development Expense													$ 0	68,600	40,800
Accrued and other liabilities									$ 23,100					23,100
Eli Lilly \| Pre-specified Events \| Maximum
License agreements
Upfront and immediate milestone payment to be received under license agreement				$ 665,000
Eli Lilly \| Development Milestones
License agreements
Amount recognized and received for the achievement of a predefined milestone														20,000	30,000	149,000
Eli Lilly \| Development Milestones \| Maximum
License agreements
Upfront and immediate milestone payment to be received under license agreement				150,000
Eli Lilly \| Regulatory Milestones
License agreements
Amount recognized and received for the achievement of a predefined milestone														$ 100,000		$ 235,000
Eli Lilly \| Regulatory Milestones \| JAPAN
License agreements
Amount recognized and received for the achievement of a predefined milestone															15,000
Eli Lilly \| Regulatory Milestones \| Europe
License agreements
Amount recognized and received for the achievement of a predefined milestone															$ 65,000
Eli Lilly \| Regulatory Milestones \| Maximum
License agreements
Upfront and immediate milestone payment to be received under license agreement				365,000
Eli Lilly \| Commercialization Milestones \| Maximum
License agreements
Upfront and immediate milestone payment to be received under license agreement				$ 150,000
Royalty payments on future global net sales (as a percent)													20.00%
Eli Lilly \| GVHD
License agreements
Upfront payment under license agreement		$ 35,000
Additional milestone payments under the license agreement		$ 40,000
Eli Lilly \| GVHD \| Regulatory Milestones
License agreements
Milestone payment made under license agreement	$ 20,000