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)	2017		2016		2017		2016
Research and development	$	596	$	476	$	1,156	$	893
General and administrative		1,462		1,590		2,926		3,182

Stock-based compensation expense	$	2,058	$	2,066	$	4,082	$	4,075

The Company granted 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. 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.

For the three months ended June 30, 2017 and 2016, 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,
	2017	2016
Risk-free interest rate	1.85 - 2.05%	1.38 - 1.54%
Expected life in years	6	6
Expected volatility	80.93 - 81.03%	80.70 - 80.81%
Expected dividend yield	0	0

The Company adopted ASU 2016-09 – Stock Compensation (Topic 718): Improvement to Employee Share-Based Payment Accounting, effective January 1, 2017. The update revises requirements in the following areas: minimum statutory withholding, accounting for income taxes, and forfeitures. Prior to adoption, the Company recognized share-based compensation, net of estimated forfeitures, over the vesting period of the grant. Upon adoption of ASU 2016-09, the Company elected to change its accounting policy to recognize forfeitures as they occur. The new forfeiture policy election was adopted using a modified retrospective approach with a cumulative effect adjustment of $122 thousand recorded to accumulated deficit as of January 1, 2017.

Stock option activity under the Company’s stock option plan for the six months ended June 30, 2017 is as follows:


	Number of Shares			Weighted- Average Exercise Price		Weighted- Average Contractual Term (Years)		Aggregate Intrinsic Value
Outstanding, December 31, 2016		3,465,335		$	5.07
Granted		265,500			6.39
Exercised		(80,000	)		4.85
Cancelled		(113,000	)		6.66

Outstanding, June 30, 2017		3,537,835		$	5.13		6.51	$	5,876

Options exercisable, June 30, 2017		2,624,335		$	4.42		5.57	$	5,400

Options exercisable, December 31, 2016		2,671,835		$	4.40		5.88	$	3,383

Options available for future grant		1,625,260

At June 30, 2017, total unrecognized compensation costs related to unvested stock options outstanding amounted to $3.0 million. The cost is expected to be recognized over a weighted-average period of 1.48 years.

A summary of the status of unvested restricted stock for the six months ended June 30, 2017 is as follows:


	Number of Shares			Weighted-Average Grant Date Fair Value
Non-vested, December 31, 2016		1,680,492		$	7.49
Granted		—			—
Vested		(350,000	)		9.35
Cancelled		—			—

Non-vested, June 30, 2017		1,330,492		$	9.46

At June 30, 2017, total unrecognized compensation costs related to unvested restricted stock outstanding amounted to $7.5 million. The cost is expected to be recognized over a weighted-average period of 1.37 years.