Stock-Based Compensation (Tables)

6 Months Ended

Jun. 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 six months ended June 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 June 30,		Six Months Ended June 30,
	2015	2014	2015	2014
Risk-free interest rate	1.87% - 1.89%	1.80% - 1.99%	1.43% - 1.89%	1.80% - 2.72%
Expected volatility	64%	65%	64% - 67%	65% - 71%
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 six months ended June 30, 2015 and 2014, the Company recognized compensation expense relating to stock options, as follows:

	Three Months Ended June 30,				Six Months Ended June 30,
	2015		2014		2015		2014
Research and development	$	280	$	159	$	478	$	231
General and administrative		420		297		668		578
Total stock option expense	$	700	$	456	$	1,146	$	809

Summary of Stock Option Award Activity

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

	Number of Shares			Weighted Average Exercise Price
Outstanding, December 31, 2014		1,022,360		$	8.16
Granted		604,000			10.45
Exercised		(34,880	)		1.02
Expired		(8,000	)		0.25
Outstanding, June 30, 2015		1,583,480			9.23
Options exercisable, June 30, 2015		456,453		$	6.25