The Company granted 18,660 and 14,635 shares of common stock to the Board during the nine months ended September 30, 2023 and 2022, respectively. The Company recognized $0.6 million and $0.4 million of stock-based compensation expense related to stock grants during the nine months ended September 30, 2023 and 2022, respectively.

During the nine months ended September 30, 2023, the Company granted 126,931 restricted stock units to certain executives that vest over three years. During the nine months ended September 30, 2022, the Company granted 1,057 and 135,054 restricted stock units to certain executives and employees that vest over one and three years, respectively.

Nonvested restricted stock units as of September 30, 2023, and changes during the nine months ended September 30, 2023 (unaudited) were as follows:


	Shares			Weighted Average Grant-Date Fair Value
Nonvested as of December 31, 2022		338,448		$	33.28
Granted		126,931			34.57
Vested		(8,426	)		35.95
Nonvested as of September 30, 2023		456,953		$	33.62

The Company's stock-based compensation expense related to the restricted stock units during the three and nine months ended September 30, 2023 and 2022 (unaudited), which was included in General and administrative expenses within the Condensed Consolidated Statements of Income, was as follows:


	Three Months Ended				Nine Months Ended
(millions)	September 30, 2023		September 30, 2022		September 30, 2023		September 30, 2022
Stock-based compensation expense	$	1.3	$	1.5	$	3.8	$	4.3

As of September 30, 2023, there was $6.9 million of unrecognized stock-based compensation expense related to restricted stock units that are expected to be recognized over a weighted average remaining period of approximately 1.8 years.

During the nine months ended September 30, 2023 and 2022, the Company granted 126,921 and 132,304 PSUs, respectively, to certain executives. The performance target 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 PSU's granted in 2023 ("2023 PSUs"), the PSU's granted in 2022 ("2022 PSUs") and the PSU's granted in 2021 ("2021 PSUs") are 253,842, 258,114 and 97,096, respectively. The Company is currently recognizing expense for the 2023 PSUs based on a payout of 134,536 shares, the 2022 PSUs based on a payout of 201,329 shares, and the maximum payout of 97,096 shares for the 2021 PSUs.

Nonvested PSUs as of September 30, 2023, and changes during the nine months ended September 30, 2023 (unaudited), were as follows:


	Shares		Weighted Average Grant-Date Fair Value
Nonvested as of December 31, 2022		177,605	$	31.94
Granted		126,921		34.57
Nonvested as of September 30, 2023		304,526	$	33.04

The Company's stock-based compensation expense related to PSUs during the three and nine months ended September 30, 2023 and 2022 (unaudited), which was included in General and administrative expenses within the Condensed Consolidated Statements of Income, was as follows:


	Three Months Ended				Nine Months Ended
(millions)	September 30, 2023		September 30, 2022		September 30, 2023		September 30, 2022
Stock-based compensation expense	$	1.4	$	0.7	$	3.7	$	1.9

As of September 30, 2023, there was $6.7 million of unrecognized stock-based compensation expenses related to PSUs that are expected to be recognized over a weighted average remaining period of approximately 1.8 years. In addition, the Company could recognize additional future stock-based compensation expenses of $4.1 million and $1.7 million for the 2023 PSUs and the 2022 PSUs, respectively, if the maximum performance target is achieved for each award.