Commitments and Contingencies - Schedule of Additional Milestone Payments under Intellectual Property License Agreements (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($)
Other Commitments [Line Items]
Cash Payments	$ 12,875
Development [Member]
Other Commitments [Line Items]
Cash Payments	1,600
Regulatory [Member]
Other Commitments [Line Items]
Cash Payments	10,275
Commercialization [Member]
Other Commitments [Line Items]
Cash Payments	$ 1,000