During the years ended December 31, 2023, 2022 and 2021, we granted performance share units (which we refer to as “PSUs”) covering up to 0.5 million, 0.5 million, and 0.2 million shares of common stock, respectively in each year, assuming maximum level of performance, with grant date fair values of $60.05, $55.93, and $58.28 per share, respectively, that are subject to both service and performance vesting conditions. The quantity of shares that will ultimately vest and be issued for the PSUs ranges from 0% to up to 250% of a targeted number of shares dependent upon the participant and will be determined based on an achievement of a three year adjusted pre-tax income performance goal. During the years ended December 31, 2023, 2022, and 2021 we issued 0.3 million, 0.3 million, and 0.3 million shares of common stock, respectively, upon the vesting and settlement of PSU that were granted in previous periods. Approximately 1.1 million shares will vest from 2024 to 2026 if the defined maximum performance targets are met, and no shares will vest if the defined minimum performance targets are not met.

During the years ended December 31, 2023, 2022 and 2021, we granted restricted stock units (which we refer to as “RSUs”) covering 0.2 million, 0.2 million and 0.2 million shares of common stock, respectively, with grant date fair values of $62.76, $62.90 and $53.21 per share, respectively, that primarily vest over a three year period. During the years ended December 31, 2023, 2022, and 2021, we

granted 12.0 thousand, 11.0 thousand and 7.0 thousand shares of common stock, respectively, on an unrestricted basis (which we refer to as “stock awards”) with grant date fair values of $65.30, $54.46 and $78.30, respectively, to our non-employee directors.

During the years ended December 31, 2023, 2022 and 2021, the Company recognized stock-based compensation expense of $36.8 million, $20.0 million and $14.4 million, respectively, which is generally included in selling, general and administrative on the consolidated statements of operations. Stock-based compensation expense for PSUs is initially estimated based on target performance achievement and adjusted as appropriate throughout the performance period. Accordingly, future compensation cost associated with outstanding PSUs may increase or decrease based on the probability and extent of achievement with respect to the applicable performance measures. During the year ended December 31, 2023, in accordance with ASC 718, Compensation—Stock Compensation, we updated our recognition of stock-based compensation expense associated with previously granted PSU awards to reflect probable financial results as they relate to the performance goals of the awards. Accordingly, our estimate of the number of shares which will ultimately vest under our PSU awards increased by a total of 0.5 million shares during the year ended December 31, 2023, of which 0.3 million shares were attributed to PSUs granted in previous periods. We recorded a cumulative catch-up adjustment to increase stock-based compensation expense of $14.5 million ($10.7 million net of tax), or $0.33 per share (basic and diluted), during the year ended December 31, 2023.

The following table summarizes the activity of our PSUs, assuming current estimated level of performance achievement, RSUs, and stock awards for the years ended December 31, 2023, 2022 and 2021 (shares in thousands):


	Year Ended December 31,
	2023			2022			2021
	Shares		Weighted average per share grant date fair value	Shares		Weighted average per share grant date fair value	Shares		Weighted average per share grant date fair value
Outstanding, beginning of year	977	$	50.78	1,104	$	31.48	1,462	$	26.76
Granted	707		61.09	428		59.41	347		55.60
Vested	(450)		36.27	(518)		27.17	(675)		29.31
Forfeited	(59)		60.86	(37)		57.79	(30)		37.68
Adjustment for PSU awards granted in previous periods	282		55.93	-		-	-		-
Outstanding, end of year	1,457	$	59.27	977	$	50.78	1,104	$	31.48

A summary of our outstanding PSUs, assuming current estimated level of performance achievement, and RSUs are as follows (in thousands, except years):