Accrued Expenses - Additional Information (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Accrued Liabilities [Line Items]
Deferred revenue	$ 20,071	$ 190
Out-license Revenue
Accrued Liabilities [Line Items]
Deferred revenue	20,000
Dunkirk, NY | Manufacturing Facility | Prepaid Expenses and Other Current Assets
Accrued Liabilities [Line Items]
Accrued construction costs to be reimbursed	$ 32,100