Stock Incentive Plan. Our stockholders have approved the issuance of up to 27.9 million shares under the Amended and Restated 2005 Stock Incentive Plan (the “2005 Plan”). This includes 2.9 million shares that were approved by our stockholders at our 2023 Annual Meeting. Shares reserved under the 2005 Plan can be granted to officers and other key employees of our Company and its subsidiaries and to non-employee directors of our Company in the form of stock options, stock appreciation rights, performance unit awards, restricted stock awards, or stock bonus awards. Shares granted under the 2005 Plan in the form of a performance unit award, restricted stock award, or stock bonus award are counted toward the aggregate number of shares of common stock available for issuance under the 2005 Plan as two shares for every one share granted or issued in payment of such award. As of December 31, 2023, 5.7 million shares were available for issuance, with 5.2 million shares available for grant.

Restricted Stock. We generally issue new shares (versus treasury shares) to fulfill restricted stock award grants. Restricted stock awards are granted at no cost to the recipient. Historically, our restricted stock awards have vested annually primarily over two to four years with no restrictions other than the passage of time (i.e., the shares are released upon calendar vesting with no further restrictions) (or “Time-Based Awards”). Unvested Time-Based Awards are typically forfeited and cancelled upon termination of employment with our Company. Certain Time-Based Awards may vest (i.e., vesting accelerates) upon a change in control, as defined, the involuntary termination of employment, or death. The fair value of the Time-Based Awards (determined by using the closing market price of our common stock on the grant date) is charged to expense on a straight-line basis over the requisite service period for the entire award.

We also issue restricted stock shares to key members of management that vest upon meeting pre-established financial and operational performance objectives (“Performance-Based Awards”) over a defined measurement period. The structure of the performance goals for the Performance-Based Awards has been approved by our stockholders. Certain Performance-Based Awards may vest (i.e., vesting accelerates) upon a change in control, as defined, or the involuntary termination of employment. The fair value of the Performance-Based Awards (determined by using the closing market price of our common stock on the grant date) is charged to expense on a straight-line basis over the performance period (generally two-years).

Additionally, we issue restricted stock to key members of management which vest upon the achievement of specified Company market valuations and conditions ("Market-Based Awards"). During 2023 and 2022, we issued Market-Based Awards to key members of management, which vest upon meeting a relative total shareholder return performance achievement tier ("rTSR Market-Based Awards") over a three-year measurement period. Certain rTSR Market-Based Awards may vest (i.e., vesting accelerates) upon a change in control, as defined, or the involuntary termination of employment. The fair value of the rTSR Market-Based Awards (determined using a Monte Carlo valuation method) is charged to expense on a straight-line basis over a three-year performance period.

A summary of our unvested restricted stock activity during 2023 is as follows (shares in thousands):


	Year Ended
	December 31, 2023
	Shares			Weighted- Average Grant Date Fair Value
Unvested awards, beginning		1,147		$	53.34
Awards granted		720			52.09
Awards forfeited/cancelled		(112	)		53.61
Awards vested		(508	)		50.52
Unvested awards, ending		1,247		$	53.61

The weighted-average grant date fair value per share of restricted stock shares granted during 2023, 2022, and 2021 was $52.09, $63.25, and $48.82, respectively. The total market value of restricted stock shares vesting during 2023, 2022, and 2021 was $28.0 million, $26.4 million, and $21.0 million, respectively.

1996 Employee Stock Purchase Plan. As of December 31, 2023, we have an employee stock purchase plan whereby 2.9 million shares of our common stock have been reserved for sale to our U.S. employees through payroll deductions. The price for shares purchased under the plan is 85% of the market value on the last day of the purchase period. Purchases are made at the end of each month. During 2023, 2022, and 2021, 73,982 shares, 58,362 shares, and 64,342 shares, respectively, were purchased under the plan for $3.3 million ($39.83 to $50.72 per share), $3.0 million ($44.95 to $55.46 per share), and $2.6 million ($36.63 to $48.98 per share), respectively. As of December 31, 2023, 1.1 million shares remain eligible for purchase under the plan.

Stock-Based Compensation Expense. We recorded stock-based compensation expense of $29.0 million, $27.2 million, and $21.4 million, respectively, for 2023, 2022, and 2021. As of December 31, 2023, there was $35.8 million of total compensation cost related to unvested awards not yet recognized. This amount, excluding the impact of forfeitures, is expected to be recognized over a weighted-average period of 1.7 years.

We recorded a deferred income tax benefit related to stock-based compensation expense during 2023, 2022, and 2021, of $6.0 million, $5.7 million, and $4.9 million, respectively. The actual income tax benefit realized for the tax deductions from the vesting of restricted stock for 2023, 2022, and 2021, totaled $4.8 million, $4.5 million, and $4.4 million, respectively.