Share-Based Compensation (Tables)

9 Months Ended

Sep. 30, 2016

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

Summary of Share-based Compensation Expense

Total share-based compensation expense related to all share-based awards for the three and nine months ended September 30, 2016 and 2015 was comprised of the following (in thousands):

	Three Months Ended   September 30,				Nine Months Ended   September 30,
	2016		2015		2016		2015
Research and development:
Stock options	$	1,678	$	636	$	4,154	$	1,609
Restricted stock	—		240		30		1,452
Warrants	10		15		25		40
Research and development share-based compensation expense	1,688		891		4,209		3,101
General and administrative:
Stock options	1,666		1,443		4,934		2,950
Restricted stock	516		545		1,645		3,719
Warrants	56		182		183		573
General and administrative share-based compensation expense	2,238		2,170		6,762		7,242
Total share-based compensation expense included in expenses	$	3,926	$	3,061	$	10,971	$	10,343

Stock Options, Valuation Assumptions

The Company estimated the fair value of each stock option grant on the grant date using the Black-Scholes model with the following weighted-average assumptions:

	Nine Months Ended   September 30,
	2016		2015
Expected volatility	141	%	147	%
Expected life (years)	5.74 years		4.91 years
Risk-free interest rate	1.3	%	1.4	%
Dividend yield	—		—

Summary of Stock Option Activity

The Company’s 2013 Equity Incentive Plan stock option activity for the nine months ended September 30, 2016 is comprised of the following:

	Outstanding Stock Options
	Shares Underlying Stock Options		Weighted- Average Exercise Price per Share
Outstanding at December 31, 2015	2,318,685		$	22.01
Granted	364,500		$	17.59
Exercised	(10,000	)	$	8.52
Forfeited	(47,700	)	$	25.76
Outstanding at September 30, 2016	2,625,485		$	21.38

Summary of Restricted Stock Activity

The Company’s restricted stock award activity for the nine months ended September 30, 2016 is comprised of the following:

	Number of Shares		Weighted- Average Grant Date Fair Market Value
Unvested at December 31, 2015	1,072,899		$	13.00
Vested	(30,220	)	$	5.53
Unvested at September 30, 2016	1,042,679		$	13.22