The Company has four equity compensation plans, adopted in 2017, 2013, 2007 and 2004 (the “Plans”) which, taken together, authorize the grant of up to 16,000,000 shares of common stock to employees, directors, and consultants. On May 23, 2019, the board of directors approved the amendment and restatement of the 2017 Omnibus Incentive Plan, which increases the number of shares available for issuance under the 2017 plan by up to 3,500,000 shares, subject to the approval of the Company’s stockholders at the Company’s 2020 annual meeting of stockholders. During the three months ended March 31, 2020, the Company approved a grant of 797,500 stock options which are contingently issuable upon approval of the increase in shares available by the stockholders. Additionally, on June 14, 2017, the Company adopted its 2017 Employee Stock Purchase Plan (the “ESPP”), which authorizes the issuance of up to 1,000,000 shares of common stock for future issuances to eligible employees.

The total fair value of stock options vested and recorded as compensation expense during the three months ended March 31, 2020 and 2019, was $1.9 million and $1.7 million, respectively. As of March 31, 2020, $13.0 million of unrecognized cost related to non-vested stock options was expected to be recognized over a weighted-average period of approximately 1.56 years. The total intrinsic value of options exercised was approximately $0.8 million and $0.4 million for the three months ended March 31, 2020 and 2019, respectively.

The following table summarizes the status of the Company’s stock option activity granted under the Plans to employees, directors, and consultants (aggregate intrinsic value in thousands):

	Stock Options			Weighted- Average Exercise price		Weighted- Average Remaining Contractual Term		Aggregate Intrinsic Value
Outstanding at December 31, 2019		10,916,936		$	8.88		5.68	$	69,785
Granted		55,045			7.32		—		—
Exercised		(70,200	)		4.84		—		—
Forfeited and expired		(58,550	)		14.45		—		—
Outstanding at March 31, 2020		10,843,231		$	8.87		5.47	$	—
Vested and exercisable at March 31, 2020		8,731,256		$	7.67		4.88	$	619

The Company determines the fair value of stock-based awards on the grant date using the Black-Scholes option pricing model, which is impacted by assumptions regarding several highly subjective variables. The following table summarizes the weighted-average assumptions used as inputs to the Black-Scholes model during the periods indicated:

	Three Months Ended			Three Months Ended
	March 31, 2020			March 31, 2019
Weighted average grant date fair value	$	7.32		$	8.03
Expected dividend yield		—	%		—	%
Expected stock price volatility		67	%		64	%
Risk-free interest rate		0.75	%		2.63	%
Expected life of options (in years)		5.0			6.3

The ESPP is available to eligible employees (as defined in the plan document). Under the ESPP, shares of the Company’s common stock may be purchased at a discount (15%) of the lesser of the closing price of the Company’s common stock on the first trading or the last trading day of the offering period. The current offering period extends from December 1, 2019 to May 31, 2020. The Company expects to offer six-month offering periods after the current period. The 2017 Plans reserved 1,000,000 shares of common stock for issuance under the ESPP. Stock-based compensation related to the ESPP amounted to $0.1 million for each of the three months ended March 31, 2020 and 2019.

The Company granted 131,000 restricted stock awards to employees during 2019. No restricted stock awards were granted during the three months ended March 31, 2020. Stock-based compensation related to the restricted stock awards amounted to $0.4 million for the three months ended March 31, 2020. As of March 31, 2020, $1.0 million of unrecognized cost related to non-vested restricted stock awards were expected to be recognized over a weighted-average period of approximately 0.4 years.

The components of stock-based compensation and the amounts recorded within research and development expenses and selling, general, and administrative expenses in the Company’s consolidated statements of operations and comprehensive loss consisted of the following for the three months ended March 31, 2020 and 2019 (in thousands):

	Three Months Ended March 31,
	2020		2019
Stock options	$	1,864	$	1,693
Restricted stock expense		397		—
Employee stock purchase plan		70		85
Total stock-based compensation expense	$	2,331	$	1,778
Cost of sales	$	54	$	64
Research and development expenses		946		591
Selling, general, and administrative expenses		1,331		1,123
Total stock-based compensation expense	$	2,331	$	1,778