The Company’s 2011 Stock Incentive Plan (the “2011 Plan”) is administered by the Company’s Board of Directors and permits the Company to grant incentive and non-qualified stock options, stock appreciation rights, restricted stock, restricted stock units and other stock-based awards.

The Company’s board of directors authorized and declared a special cash dividend of $20.0 million to holders of the Company's common stock, which was payable on September 5, 2019 to stockholders of record as of the close of business on August 28, 2019. The board of directors determined, in accordance with the adjustment provision of the 2011 Plan, that the special cash dividend was unusual and non-recurring and that appropriate adjustment to the stock options to purchase shares of the Company’s common stock outstanding under the 2011 Plan was required. The Company treated this adjustment as a modification to the original stock option grant because the terms of the agreements were modified in order to preserve the value of the option awards after a large non-recurring cash dividend. These options were amended to decrease the exercise price and increase the shares subject to the stock option. However, as the fair value of the underlying stock decreased more than the exercise price upon modification, and the result was a decrease in the fair value of such options. Accordingly, no incremental value was provided and no additional compensation cost was recorded by the Company.

At September 30, 2019, there were 1.2 million shares remaining available for grant under the 2011 Plan. The weighted-average grant date fair value per share of stock options granted during the three and nine months ended September 30, 2019 was $3.53. The weighted-average grant date fair value per share of stock options granted during the nine months ended September 30, 2018.

The fair value of stock options granted to employees during the nine months ended September 30, 2019 and 2018 was estimated at the date of grant using the following assumptions:

	Nine Months Ended September 30,
	2019			2018
Risk-free interest rate		1.8	%	2.3 – 2.9%
Expected dividend yield		0	%	0%
Expected term	5.4 years			5.3 - 5.8 years
Expected volatility		67	%	62 – 64%

The Company recognized stock-based compensation expense during the three and nine months ended September 30, 2019 and 2018 as follows:

	Three Months Ended September 30,				Nine Months Ended September 30,
(in thousands)	2019		2018		2019		2018
Research and development expense	$	—	$	256	$	223	$	870
General and administrative expense		703		526		1,561		1,456
Total stock-based compensation expense	$	703	$	782	$	1,784	$	2,326