Common Stock Reserved for Issuance (Tables)

9 Months Ended

12 Months Ended

Sep. 30, 2015

Dec. 31, 2014

Equity [Abstract]

Schedule of Common Stock Reserved for Future Issuance

The common stock reserved for future issuance at December 31, 2013 and 2014 was as follows:

	December 31,
	2013		2014
Conversion of outstanding convertible preferred stock		25,036,330		27,654,928
Shares underlying outstanding stock options		2,723,406		4,248,504
Shares available for future stock option grants		1,848,367		295,101
Warrant to purchase convertible preferred stock		128,231		128,231
Total shares of common stock reserved		29,736,334		32,326,764

Summary of Assumptions to Use Option Pricing Model

The placement warrants were valued at their grant dates using the Black-Scholes pricing model and the following weighted average assumptions:

	September 30, 2015
Common Stock Warrant:
Expected term (in years)		5.0
Expected volatility		31.8	%
Risk-free interest rate		1.6	%
Expected dividend yield		0	%

The Company used the Black-Scholes option-pricing model to estimate the fair value of the convertible preferred stock warrant with the following assumptions:

	December 31,
	2013			2014
Series C Warrant:
Expected term (in years)		2.0			5.3
Expected volatility		30.0	%		30.0	%
Risk-free interest rate		0.4	%		1.7	%
Expected dividend yield		0	%		0	%