Stock-Based Compensation (Tables)

9 Months Ended

Sep. 30, 2015

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Summary of Assumptions Used in Black-Scholes Option Pricing Model

The fair values of stock options granted during the three and nine months ended September 30, 2015 and 2014 were estimated as of the dates of grant using the Black-Scholes option pricing model with the following assumptions:

	Three Months Ended September 30,		Nine Months Ended September 30,
	2015	2014	2015	2014
Risk-free interest rate	1.77%	1.92%	1.43% - 1.89%	1.80% - 2.72%
Expected volatility	64.1%	65.0%	64.0% - 67.1%	65.0% - 71.0%
Expected dividend yield	0%	0%	0%	0%
Expected life of employee options (in years)	6.25	6.25	6.25	6.25
Expected life of nonemployee options (in years)	10	10	10	10

Summary of Compensation Expense Relating to Stock Options

During the three and nine months ended September 30, 2015 and 2014, the Company recognized compensation expense relating to stock options, as follows:

	Three Months Ended September 30,				Nine Months Ended September 30,
	2015		2014		2015		2014
Research and development	$	283	$	38	$	761	$	269
General and administrative		378		184		1,046		762
Total stock option expense	$	661	$	222	$	1,807	$	1,031

Summary of Stock Option Award Activity

A summary of stock option award activity as of and for the nine months ended September 30, 2015 is presented below:

	Number of Shares			Weighted Average Exercise Price
Outstanding, December 31, 2014		1,022,360		$	8.16
Granted		629,000			10.91
Exercised		(101,588	)		3.18
Expired		(8,000	)		0.25
Outstanding, September 30, 2015		1,541,772			9.65
Options exercisable, September 30, 2015		433,806		$	7.00