During the three months ended March 31, 2024 and 2023, the Company granted 158,343 and 126,931 RSU's, respectively, to certain executives that vest over three years.

Nonvested RSU's as of March 31, 2024, and changes during the three months ended March 31, 2024 (unaudited) were as follows:


	Shares			Weighted Average Grant-Date Fair Value
Nonvested as of December 31, 2023		290,787		$	32.89
Granted		158,343			54.00
Vested		(4,694	)		31.96
Nonvested as of March 31, 2024		444,436		$	40.39

The Company's stock-based compensation expense related to RSU's during the three months ended March 31, 2024 and 2023 (unaudited), which was included in General and administrative expenses within the Condensed Consolidated Statements of Income, was as follows:


	Three Months Ended
(millions)	March 31, 2024		March 31, 2023
Stock-based compensation expense	$	1.4	$	1.1

As of March 31, 2024, there was $12.6 million of unrecognized stock-based compensation expense related to RSU's that are expected to be recognized over a weighted average remaining period of approximately 2.3 years.

There were 251,462 nonvested PSU's outstanding at a weighted average grant-date fair value of $32.66 as of March 31, 2024 and December 31, 2023. There were no changes during the three months ended March 31, 2024.

During the three months ended March 31, 2023, the Company granted 126,921 PSU's ("2023 PSU's") to certain executives. The performance target for PSU's is based on the achievement of a certain level of operating income, excluding depreciation and amortization, as well as certain other discretionary adjustments by the Board, over a three-year performance period. The ultimate number of shares issued could change depending on the Company’s results over the performance period. The maximum amount of shares that could be issued for the 2023 PSU's and the PSU's granted in 2022 ("2022 PSU's") are 248,056 and 254,868, respectively. The Company is currently recognizing expense for the 2023 PSU's and 2022 PSU's based on a payout of 126,509 shares and 193,700 shares, respectively.

The Company's stock-based compensation expense related to PSU's during the three months ended March 31, 2024 and 2023 (unaudited), which was included in General and administrative expenses within the Condensed Consolidated Statements of Income, was as follows:


	Three Months Ended
(millions)	March 31, 2024		March 31, 2023
Stock-based compensation expense	$	0.9	$	1.1

As of March 31, 2024, there was $4.2 million of unrecognized stock-based compensation expenses related to PSU's that are expected to be recognized over a weighted average remaining period of approximately 1.4 years. In addition, the Company could recognize additional future stock-based compensation expenses of $4.2 million and $1.9 million for the 2023 PSU's and 2022 PSU's, respectively, if the maximum performance target is achieved for each award.