Significant Agreements - Celgene, Accounting Analysis (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Significant Agreements
Revenue from contract with customer	$ 39,752	$ 27,666	$ 44,096	$ 30,447
REBLOZYL Agreement | Collaboration, License, and Option Agreement
Significant Agreements
Payments received			219,600
Revenue from contract with customer	25,000
Sotarcept | Collaboration, License, and Option Agreement
Significant Agreements
Payments received			44,900
Regulatory Milestone | Luspatercept | Collaboration, License, and Option Agreement
Significant Agreements
Collaborative arrangement potential milestone payments on acceptance of regulatory application	$ 20,000		$ 20,000