Stock-Based Compensation (Tables)

9 Months Ended

Sep. 30, 2016

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, 2016 and 2015 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,
	2016	2015	2016	2015
Risk-free interest rate	1.19%	1.77%	1.19% - 1.79%	1.43% - 1.89%
Expected volatility	71.9%	64.1%	67.8% - 72.6%	64.0% - 67.1%
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

Summary of Compensation Expense Relating to Stock Options

During the three and nine months ended September 30, 2016 and 2015, the Company recognized compensation expense relating to stock options, as follows:

	Three Months Ended September 30,				Nine Months Ended September 30,
	2016		2015		2016		2015
Research and development	$	375	$	283	$	867	$	761
General and administrative		402		378		1,104		1,046
Total stock option expense	$	777	$	661	$	1,971	$	1,807

Summary of Stock Option Award Activity

A summary of stock option award activity related to employees, non-employee members of the Company’s Board of Directors and non-employee consultants as of and for the nine months ended September 30, 2016 is presented below:

	Number of Shares			Weighted Average Exercise Price
Outstanding, December 31, 2015		1,658,408		$	10.27
Granted		797,000			5.99
Exercised		(28,000	)		1.41
Forfeited		(95,792	)		12.15
Expired		(32,499	)		11.03
Outstanding, September 30, 2016		2,299,117			8.80
Options exercisable, September 30, 2016		887,213		$	8.98