Significant Accounting Policies - Summary of Changes in Level 3 Instruments Measured at Fair Value On Recurring Basis (Detail) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance as of January 1	$ 850
Level 3
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance as of January 1	850	$ 650
Change in fair value of warrant liability	341	200
Reclassification of warrant liability to equity	(1,191)	0
Balance as of September 30	$ 0	$ 850