Accrued Expenses and Other Current Liabilities - Schedule of Accrued Expenses and Other Current Liabilities (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Payables And Accruals [Abstract]
Research and development	$ 1,372	$ 1,216
Payroll and other employee-related expenses	5,683	8,207
Professional services fees	4,281	2,544
Interest expense	2,879	1,195
Product revenue reserves	628	616
Accrual for employee stock purchase plan	740	251
Other	202	281
Total accrued expenses and other current liabilities	$ 15,785	$ 14,310