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 March 31,
(in thousands)	2018		2017
Research and development	$	603	$	560
General and administrative		3,056		1,464

Stock-based compensation expense	$	3,659	$	2,024

The Company granted an aggregate of 7,500 stock options during the three months ended March 31, 2018 with a weighted-average grant date fair value of $3.00 per share. The Company granted an aggregate of 117,000 stock options during the three months ended March 31, 2017 with a weighted-average grant date fair value of $4.48 per share.

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 months ended March 31, 2018.

For the three months ended March 31, 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 March 31,
	2018	2017
Risk-free interest rate	2.56 - 2.74%	2.04 - 2.23%
Expected life in years	6	6
Expected volatility	80.75 - 81.10%	80.31 - 80.90%
Expected dividend yield	0	0

The Company accounts for forfeitures under 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 three months ended March 31, 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		7,500			4.27
Exercised		—			—
Cancelled		(36,667	)		5.93

Outstanding, March 31, 2018		3,822,968		$	5.08		6.20	$	1,020

Options exercisable, March 31, 2018		2,951,502		$	4.83		5.36	$	1,019

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

Options available for future grant		403,962

At March 31, 2018, total unrecognized compensation costs related to unvested stock options outstanding amounted to $5.0 million. The cost is expected to be recognized over a weighted-average period of 1.70 years.

A summary of the status of unvested restricted stock for the three months ended March 31, 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		(205,491	)		5.38
Cancelled		(70,867	)		5.07

Non-vested, March 31, 2018		1,532,201		$	5.82

At March 31, 2018, total unrecognized compensation costs related to unvested restricted stock outstanding amounted to $7.9 million. The cost is expected to be recognized over a weighted-average period of 1.48 years.