We have stock option and stock incentive plans for employees and non-employee Directors that provide for grants of restricted stock awards (“RSAs”), restricted stock units (“RSUs”), performance stock units (“PSUs”), and options to purchase shares of our common stock at exercise prices generally equal to the fair value of such stock at the dates of grant. We also maintain a shareholder-approved Employee Stock Purchase Plan (the “ESPP”) for the benefit of our employees. The ESPP allows eligible employees to purchase common stock on a regular basis at the lower of 85% of the market price at the beginning or end of each offering period.

During the six months ended June 30, 2019 the Compensation Committee of our Board of Directors (the “Committee”) authorized awards from approved stock incentive plans of RSUs to certain employees, RSAs to non-employee Directors and RSAs and PSUs to certain Company officers, which, assuming that performance under the PSUs were to be achieved at target levels, together totaled 492,000 shares and had an aggregate grant date market value of $14.6 million. Two types of PSUs were granted in 2019, one with a short-term performance component and the other with a long-term performance component. If performance thresholds are met, the short-term PSUs granted in 2019 represent the right to receive up to 150% of the target number of shares of common stock. The performance component of the short-term PSU awards granted in 2019 is based on attaining specified levels of adjusted earnings before interest, taxes, depreciation, and amortization, (“EBITDA”), as defined in the PSU grant documents, for the 2019 calendar year. If performance thresholds are met, the long-term PSUs granted in 2019 represent the right to receive up to 288% of the target number of shares of common stock. The performance component of the long-term PSU awards granted in 2019 is based on attaining specified levels of adjusted revenue growth and gross margin, as defined in the PSU grant document, for the years 2019 through 2023. We currently believe that achievement of the performance component for both types of PSUs is probable, and we reevaluate this likelihood on a quarterly basis.

During the six months ended June 30, 2018 the Committee authorized awards from approved stock incentive plans of RSUs to certain employees, RSAs to non-employee Directors and RSAs and PSUs to certain Company officers, which, including PSUs at target levels, together totaled 305,000 shares of common stock and had an aggregate grant date market value of $6.8 million. The PSUs granted in 2018 represented the right to receive up to 150% of the target number of shares of common stock based on meeting performance thresholds. The performance component of PSU awards granted in 2018 was based on attaining specified levels of adjusted EBITDA, as defined in the PSU grant documents, for the 2018 calendar year. The PSUs granted in 2018 earned 80% of the target number of shares.

The Committee authorized, from approved stock incentive plans, grants of stock options to purchase a total of 169,000 and 219,000 shares to certain Company officers during the six months ended June 30, 2019 and 2018, respectively. The exercise prices of the options were equal to the closing stock prices on their respective grant dates.

Employees purchased common stock totaling 24,000 shares and 36,000 shares in the six months ended June 30, 2019 and 2018, respectively, through the ESPP. There were no purchases of shares through the ESPP during the three months ended June 30, 2019 and 2018.

The following weighted-average assumptions were used to determine the fair value of options and shares purchased under the ESPP:


	Three Months Ended				Six Months Ended
	June 30, 2019				June 30, 2019
	Stock Options		ESPP		Stock Options		ESPP
Expected life		N/A		0.5 Years		5.0 Years		0.5 Years
Expected stock price volatility		N/A		0.39		0.40		0.39
Risk-free interest rate		N/A		2.56%		2.54%		2.56%

The following table summarizes total stock compensation expenses prior to the capitalization of amounts into deferred preservation and inventory costs (in thousands):


	Three Months Ended				Six Months Ended
	June 30,				June 30,
	2019		2018		2019		2018
RSA, RSU, and PSU expense	$	1,936	$	1,521	$	3,446	$	2,469
Stock option and ESPP expense		502		483		973		889
Total stock compensation expense	$	2,438	$	2,004	$	4,419	$	3,358

Included in the total stock compensation expense, as applicable in each period, were expenses related to RSAs, RSUs, PSUs, and stock options issued in each respective year, as well as those issued in prior periods that continue to vest during the period, and compensation related to the ESPP. These amounts were recorded as stock compensation expense and were subject to our normal allocation of expenses to inventory costs and deferred preservation costs. We capitalized $168,000 and $300,000 in the three and six months ended June 30, 2019, respectively, and $132,000 and $238,000 in the three and six months ended June 30, 2018, respectively, of the stock compensation expense into our inventory costs and deferred preservation costs.

As of June 30, 2019 we had total unrecognized compensation costs of $16.1 million related to RSAs, RSUs, and PSUs and $2.8 million related to unvested stock options. As of June 30, 2019 this expense is expected to be recognized over a weighted-average period of 2.8 years for PSUs, 2.0 years for stock options, 1.9 years for RSUs, and 1.5 years for RSAs.