Accrued Expenses - Schedule of Accrued Expenses (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Accrued Liabilities Current [Abstract]
Payroll and employee-related costs	$ 8,174	$ 7,321
Research costs	9,853	7,973
Licensing fees	26	625
Professional fees	2,537	1,848
Intellectual property costs	1,739	2,193
Accrued property and equipment	53	294
Other	15	598
Total	$ 22,397	$ 20,852