Preferred Stock Warrant Liability - Summary of Assumptions and Inputs Used in Determining Fair Value of Preferred Stock Warrant Liability Valued Using Black-Scholes Option-Pricing Model (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2013
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Risk-free interest rate	1.83%
Expected term (in years)	8 years 6 months
Expected volatility	80.00%
Expected dividend yield	0.00%
Fair value of Series A-2 convertible preferred stock		$ 0	$ 0
Series A-2 Convertible Preferred Stock [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Fair value of Series A-2 convertible preferred stock	$ 14,870			$ 156,000