10. 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)	2015		2014		2015		2014
Research and development	$	316	$	410	$	610	$	786
General and administrative		3,169		802		3,967		1,649

Stock-based employee compensation expense	$	3,485	$	1,212	$	4,577	$	2,435

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. The Company granted an aggregate of 23,800 and 104,300 stock options during the three and six months ended June 30, 2014 with a weighted-average grant date fair value of $2.84 and $3.23 per share, respectively.

On March 31, 2014, the Company extended the contractual life of 71,167 fully vested stock options held by one employee by an additional 9 months.

On March 31, 2014, the Company extended the contractual life of 33,333 fully vested stock options and 66,667 unvested stock options held by one employee.

On September 8, 2014, the Company extended the contractual life of 82,834 fully vested stock options and 23,333 unvested stock options held by one employee by an additional 3 months.

On September 15, 2014, the Company extended the contractual life of 39,167 fully vested stock options and 113,333 unvested stock options held by one employee.

On June 17, 2015, the Company extended the contractual life of 157,500 fully vested stock options held by a director.

For the three months ended June 30, 2015 and 2014, 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,
	2015			2014
Risk-free interest rate		1.69	%		1.98	%
Expected life in years		6			6
Expected volatility		85.57	%		94.07	%
Expected dividend yield		0			0

Stock option activity under the Company’s stock option plan for the three months ended June 30, 2015 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, 2014		6,505,663		$	4.07
Granted		51,800			9.11
Exercised		(2,860,299	)		3.97
Cancelled		(153,833	)		4.13

Outstanding, June 30, 2015		3,543,331		$	4.23		3.89	$	27,534

Vested and unvested expected to vest at June 30, 2015		3,491,349		$	4.12		5.76	$	27,130

Options exercisable, June 30, 2015		1,912,531		$	4.12		5.76	$	15,074

Options exercisable, December 31, 2014		3,781,162		$	4.10		5.80	$	4,130

Options available for future grant		3,635,802

At June 30, 2015, 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 1.49 years.

During the three months ended June 30, 3015, the Company issued 1,050,000 shares of restricted stock to employees, which vests ratably in annual installments over three years, commencing on the first anniversary of the grant date. No shares of restricted stock were issued during the three or six months ended June 30, 2014.

A summary of the status of unvested restricted stock for the three months ended June 30, 2015 is as follows:


	Number of Shares			Weighted-Average Grant Date Fair Value
Non-vested, December 31, 2014		144,508		$	4.70
Granted		1,050,000			9.35
Vested		(70,991	)		4.62
Cancelled		—			—

Non-vested, June 30, 2015		1,123,517		$	9.05

At June 30, 2015, total unrecognized compensation costs related to unvested restricted stock outstanding amounted to $9.5 million. The cost is expected to be recognized over a weighted-average period of 1.93 years.