Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Accrued expenses
Accrued development milestones	$ 26,881	$ 12,000
Accrued employee compensation and benefits	32,195	3,521
Accrued clinical trial costs	13,238	16,476
Accrued commercialization and other professional fees	13,713	15,408
Other accrued expenses and current liabilities	32,096	4,697
Total accrued expenses and other current liabilities	$ 118,123	$ 52,102