License Agreements - Novartis (Details) - USD ($) $ in Thousands	1 Months Ended					3 Months Ended								12 Months Ended			134 Months Ended
	Apr. 30, 2016	Sep. 30, 2014	Jan. 31, 2010	Dec. 31, 2009	Nov. 30, 2009	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2020
License agreements
Revenues						$ 789,509	$ 620,643	$ 688,043	$ 568,507	$ 579,389	$ 551,581	$ 529,932	$ 497,857	$ 2,666,702	$ 2,158,759	$ 1,881,883
U.S.
License agreements
Revenues														2,600,000	2,100,000	1,800,000
Europe
License agreements
Revenues														105,000	90,000	79,900
JAKAFI
License agreements
Revenues														1,937,850	1,684,968	1,386,964
Novartis
License agreements
Upfront and immediate milestone payment to be received under license agreement					$ 210,000
Upfront payment received under license agreement				$ 150,000
Immediate milestone payment received under license agreement			$ 60,000
Revenues														170,000	0	60,000
Reimbursable costs included in accounts receivable						200				400				200	400		$ 200
Research and development expenses reimbursed														300	1,500	3,200
Novartis | Pre-specified Events | Maximum
License agreements
Upfront and immediate milestone payment to be received under license agreement					1,200,000
Novartis | Development Milestones
License agreements
Amount recognized and received for the achievement of a predefined milestone																	157,000
Novartis | Development Milestones | Maximum
License agreements
Upfront and immediate milestone payment to be received under license agreement					174,000
Novartis | Regulatory Milestones
License agreements
Amount recognized and received for the achievement of a predefined milestone																	280,000
Novartis | Regulatory Milestones | Maximum
License agreements
Upfront and immediate milestone payment to be received under license agreement					495,000
Novartis | Sales and Commercial Milestones
License agreements
Amount recognized and received for the achievement of a predefined milestone																	200,000
Novartis | Sales and Commercial Milestones | Maximum
License agreements
Upfront and immediate milestone payment to be received under license agreement					$ 500,000
Novartis | TABRECTA
License agreements
Revenues														4,100
Novartis | TABRECTA | Development Milestones
License agreements
Amount recognized and received for the achievement of a predefined milestone														25,000
Novartis | TABRECTA | Regulatory Milestones
License agreements
Amount recognized and received for the achievement of a predefined milestone														45,000
Novartis | TABRECTA | Regulatory Milestones | JAPAN
License agreements
Amount recognized and received for the achievement of a predefined milestone														20,000
Novartis | GVHD | Development and Regulatory Milestones | Maximum
License agreements
Upfront and immediate milestone payment to be received under license agreement	$ 75,000
Novartis | JAKAFI | U.S.
License agreements
Revenues														89,900	77,600	63,000
Royalties payable						$ 96,400				$ 50,200				96,400	50,200		$ 96,400
Novartis | JAKAVI
License agreements
Revenues														$ 277,900	$ 225,900	194,700
Novartis | JAKAVI | Minimum
License agreements
Royalty payments on future global net sales (as a percent)														12.00%
Novartis | JAKAVI | Maximum
License agreements
Royalty payments on future global net sales (as a percent)														14.00%
Novartis | JAKAVI | Regulatory Milestones | Europe
License agreements
Amount recognized and received for the achievement of a predefined milestone		$ 60,000
Novartis | JAKAVI | Sales and Commercial Milestones
License agreements
Amount recognized and received for the achievement of a predefined milestone														$ 80,000		60,000
Revenues														$ 1,200,000		$ 900,000