Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Accrued expenses
Accrued development milestones	$ 7,167	$ 12,000
Accrued employee compensation and benefits	19,835	3,521
Accrued clinical trial costs	15,097	16,476
Accrued commercialization and other professional fees	12,244	15,408
Other accrued expenses and current liabilities	71,924	4,697
Total accrued expenses and other current liabilities	$ 126,267	$ 52,102