8. 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)	2018		2017		2018		2017
Research and development	$	609	$	596	$	1,212	$	1,156
General and administrative		1,102		1,462		4,158		2,926

Stock-based compensation expense	$	1,711	$	2,058	$	5,370	$	4,082

The Company granted an aggregate of 198,000 and 205,500 stock options during the three and six months ended June 30, 2018 with a weighted-average grant date fair value of $3.06 and $3.06 per share, respectively. The Company granted an aggregate of 148,500 and 265,500 stock options during the three and six months ended June 30, 2017 with a weighted-average grant date fair value of $4.48 and $4.45 per share, respectively.

On February 15, 2018, the Company extended the contractual life of 751,667 fully vested stock options held by one officer of the Company by an additional 9 months. Additionally, on March 12, 2018, the Company extended the contractual life of 117,500 fully vested stock options held by a director. These extensions resulted in additional stock compensation expense of $481 thousand in the three and six months ended June 30, 2018.

The Company recognizes forefeitures as they occur. For the three months ended June 30, 2018 and 2017, 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,
	2018	2017
Risk-free interest rate	2.66 - 2.91%	1.85 - 2.05%
Expected life in years	6	6
Expected volatility	81.48 - 81.66%	80.93 - 81.03%
Expected dividend yield	0	0

Stock option activity under the Company’s stock option plan for the six months ended June 30, 2018 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, 2017		3,852,135		$	5.12
Granted		205,500			4.32
Exercised		(104,167	)		2.30
Cancelled		(149,666	)		5.50

Outstanding, June 30, 2018		3,803,802		$	5.08		6.14	$	415

Options exercisable, June 30, 2018		2,840,835		$	4.97		5.16	$	415

Options exercisable, December 31, 2017		2,925,502		$	5.12		5.58	$	1,152

Options available for future grant		318,961

At June 30, 2018, 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 1.62 years.

In September 2017, the Company issued a stock option award as an inducement grant for the purchase of an aggregate of 500,000 shares of the Company’s common stock, outside of the 2012 Plan, at an exercise price of $6.19 per share. The inducement grant is excluded from the option activity table above.

A summary of the status of unvested restricted stock for the six months ended June 30, 2018 is as follows:


	Number of Shares			Weighted-Average Grant Date Fair Value
Non-vested, December 31, 2017		1,808,559		$	5.74
Granted		—			—
Vested		(538,824	)		7.84
Cancelled		(70,867	)		5.07

Non-vested, June 30, 2018		1,198,868		$	4.83

At June 30, 2018, total unrecognized compensation costs related to unvested restricted stock outstanding amounted to $4.3 million. The cost is expected to be recognized over a weighted-average period of 1.56 years.