Accrued Expenses and Other Current Liabilities (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Accrued expenses and other liabilities:
Accrued compensation and benefits	$ 6,890	$ 7,886
Accrued consulting and professional fees	3,601	3,841
Accrued research and development	1,742	1,855
Accrued other	7,783	5,357
Total accrued expenses and other current liabilities	$ 20,016	$ 18,939