Warrant Liabilities - Summary of Assumptions Used Black-Scholes Option-Pricing Model (Details) - $ / shares	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
Convertible Preferred Stock Warrants | Minimum
Class Of Warrant Or Right [Line Items]
Expected term (in years)	1 year	1 year 9 months 15 days
Fair value of underlying shares	$ 10.80	$ 0.67
Volatility	79.20%	63.10%
Risk-free interest rate	0.23%	0.38%
Convertible Preferred Stock Warrants | Maximum
Class Of Warrant Or Right [Line Items]
Expected term (in years)	6 years 15 days	7 years 15 days
Fair value of underlying shares	$ 12.24	$ 1.56
Volatility	111.10%	80.80%
Risk-free interest rate	1.54%	2.30%
Common Stock Warrants | Minimum
Class Of Warrant Or Right [Line Items]
Expected term (in years)	6 years	6 years 9 months 15 days
Fair value of underlying shares	$ 15.00	$ 1.03
Volatility	82.00%	76.30%
Risk-free interest rate	1.51%	2.13%
Common Stock Warrants | Maximum
Class Of Warrant Or Right [Line Items]
Expected term (in years)	6 years 6 months 29 days	7 years 6 months 29 days
Fair value of underlying shares	$ 42.00	$ 1.07
Volatility	82.60%	80.40%
Risk-free interest rate	1.63%	2.41%