Stock-Based Compensation - Summary of Warrant Activity (Detail) - Outstanding Warrants	9 Months Ended
	Sep. 30, 2017 shares
Warrant [Line Items]
Warrants, Beginning Balance	17,768,314
Warrants exercised	(32,787)
Warrants, Ending Balance	17,735,527
Warrants, Vested and exercisable Ending Balance	15,884,027