Fair Value Measurements - Schedule of Remeasured Preferred Stock Warrants to Fair Value using OPM and/or PWERM Models (Detail)		12 Months Ended
	Dec. 31, 2014	Dec. 31, 2014
Class of Stock [Line Items]
Expected dividend rate		0.00%
Outstanding Preferred Stock Warrants [Member]
Class of Stock [Line Items]
Expected dividend rate	0.00%
Minimum [Member]
Class of Stock [Line Items]
Expected term (in years)		1 year 2 months 12 days
Expected volatility		69.00%
Risk-free interest rate		0.30%
Minimum [Member] | Outstanding Preferred Stock Warrants [Member]
Class of Stock [Line Items]
Expected term (in years)	1 year 2 months 12 days
Expected volatility	69.00%
Risk-free interest rate	0.30%
Expected dividend rate	0.00%
Discount for lack of marketability	19.50%
Maximum [Member]
Class of Stock [Line Items]
Expected term (in years)		2 years 6 months
Expected volatility		86.00%
Risk-free interest rate		0.60%
Maximum [Member] | Outstanding Preferred Stock Warrants [Member]
Class of Stock [Line Items]
Expected term (in years)	2 years 6 months
Expected volatility	86.00%
Risk-free interest rate	0.60%
Expected dividend rate	0.00%
Discount for lack of marketability	24.30%