Accrued Expenses (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Accrued Liabilities and Other Liabilities [Abstract]
Accrued compensation	$ 4,397	$ 4,014
Accrued research and development expenses	3,414	2,384
Accrued professional expenses	1,049	735
Other accrued expenses	347	411
Other restructuring expenses	173
Total	$ 9,380	$ 7,544