Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Accrued expenses
Accrued development milestones	$ 32,801	$ 12,000
Accrued employee compensation and benefits	9,462	3,521
Accrued clinical trial costs	9,736	16,476
Accrued commercialization and other professional fees	17,864	15,408
Other accrued expenses and current liabilities	6,907	4,697
Total accrued expenses and other current liabilities	$ 76,770	$ 52,102