Accrued Expenses - Components of Accrued Expenses (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Payables and Accruals [Abstract]
Accrued clinical	$ 43,976	$ 61,815
Product revenue allowances	38,772	30,552
Accrued payroll	12,432	12,604
MTPC - Supply of Validation Drug Product	5,904	0
Lease liability	$ 5,317	$ 4,989
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	us-gaap:AccruedLiabilitiesCurrent	us-gaap:AccruedLiabilitiesCurrent
Royalties	$ 2,868	$ 2,713
Professional fees	2,262	3,444
Accrued commercial manufacturing	634	2,680
Accrued severance	528	725
Accrued other	10,328	9,549
Total accrued expenses	$ 123,021	$ 129,071