Stock-Based Compensation

6 Months Ended

Jun. 30, 2016

Stock-Based Compensation

7. Stock-Based Compensation

The Company recognized stock-based compensation expense on all employee and non-employee awards as follows:

	For the three months ended June 30,				For the six months ended June 30,
(in thousands)	2016		2015		2016		2015
Research and development	$	476	$	316	$	893	$	610
General and administrative		1,590		3,169		3,182		3,967
Stock-based compensation expense	$	2,066	$	3,485	$	4,075	$	4,577

The Company granted an aggregate of 116,000 and 136,000 stock options during the three and six months ended June 30, 2016 with a weighted-average grant date fair value of $5.91 and $5.62 per share, respectively. The Company granted an aggregate of 1,800 and 51,800 stock options during the three and six months ended June 30, 2015 with a weighted-average grant date fair value of $6.85 and $6.59 per share, respectively.

For the three months ended June 30, 2016 and 2015, the fair value of stock options was estimated on the date of grant using a Black-Scholes option valuation model with the following assumptions:

	For the three months ended June 30,
	2016	2015
Risk-free interest rate	1.38 - 1.54%	1.69%
Expected life in years	6	6
Expected volatility	80.70 - 80.81%	85.57%
Expected dividend yield	0	0

Stock option activity under the Company’s stock option plan for the six months ended June 30, 2016 is as follows:

(in thousands, except share and per share data)	Number of Shares			Weighted- Average Exercise Price		Weighted- Average Contractual Term (Years)		Aggregate Intrinsic Value
Outstanding, December 31, 2015		3,481,469		$	4.96
Granted		136,000			8.13
Exercised		(169,000	)		4.81
Cancelled		(10,366	)		6.48
Outstanding, June 30, 2016		3,438,103		$	5.08		6.75	$	4,046
Vested and unvested expected to vest at June 30, 2016		3,353,760		$	5.08		5.71	$	3,947
Options exercisable, June 30, 2016		2,237,935		$	5.08		5.71	$	3,430
Options exercisable, December 31, 2015		2,120,834		$	4.24		5.84	$	8,622
Options available for future grant		2,642,596

At June 30, 2016, total unrecognized compensation costs related to unvested stock options outstanding amounted to $4.2 million. The cost is expected to be recognized over a weighted-average period of 1.54 years.

A summary of the status of unvested restricted stock for the six months ended June 30, 2016 is as follows:

	Number of Shares			Weighted- Average Grant Date Fair Value
Non-vested, December 31, 2015		1,586,388		$	9.00
Granted		—			—
Vested		(350,000	)		9.35
Cancelled		—			—
Non-vested, June 30, 2016		1,236,388		$	9.00

At June 30, 2016, total unrecognized compensation costs related to unvested restricted stock outstanding amounted to $9.4 million. The cost is expected to be recognized over a weighted-average period of 1.53 years.