Accrued Expenses and Other Current Liabilities - Additional Information (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Accrued Expenses
Other accrued expenses	$ 8,688	$ 12,157
Write-down of excess non-cancellable ZURAMPIC sample purchase commitments		1,300
Other accrued expenses, finished goods inventory	200	200
Commercial and Sample Supply Commitments
Accrued Expenses
Accrual for non-cancellable purchase commitments	$ 2,500	$ 3,400