Notes Payable - Summary of Future Principal Payments Including Paid In-Kind Interest under Innovatus Loan Agreement (Detail) - Loan and Security Agreement [Member] - Innovatus Life Sciences Lending Fund I, LP [Member] - Term Loan [Member] $ in Thousands	Dec. 31, 2017 USD ($)
Debt Instrument [Line Items]
2018	$ 4,788
2019	7,181
2020	2,394
Total	$ 14,363