There were 13,420 and 25,066 stock grants granted during the six months ended June 30, 2021 and 2020, respectively. The Company recognized $0.5 million of stock-based compensation expense related to stock grants for the three and six months ended June 30, 2021 and 2020.

During the six months ended June 30, 2021, the Company granted 160,843 and 152,659 restricted stock units to certain executives and employees that vest over two and three years, respectively.

Nonvested restricted stock units as of June 30, 2021, and changes during the six months ended June 30, 2021 (unaudited) were as follows:

	Shares		Weighted Average Grant-Date Fair Value
Nonvested as of December 31, 2020		51,276	$	33.24
Granted		313,502		34.45
Nonvested as of June 30, 2021		364,778	$	34.28

The Company's stock-based compensation expense related to the restricted stock units for the three and six months ended June 30, 2021 and 2020 (unaudited), respectively, which is included in General and administrative expenses within the Condensed Consolidated Statements of Income (Loss), was as follows:

	Three Months Ended				Six Months Ended
(millions)	June 30, 2021		June 30, 2020		June 30, 2021		June 30, 2020
Stock-based compensation expense	$	1.3	$	0.3	$	2.1	$	0.6

As of June 30, 2021, there was $9.3 million of unrecognized stock-based compensation costs related to the restricted stock units that are expected to be recognized over a weighted average remaining period of approximately 1.9 years.

During the six months ended June 30, 2021, the Company granted 50,868 performance share units to certain executives. The performance target is based on the achievement of a certain level income from operations, excluding depreciation and amortization, as well as certain other discretionary adjustments by the Board, over the three-year performance period from 2021 through 2023. 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 shares granted in 2021 are 101,736. The Company is currently recognizing expense based on maximum payout of 101,736 shares.

Due to the impact of COVID-19 on the Company’s operations, the Company expects the targets for the PSU awards granted in 2019 (“2019 PSU’s) and 2020 (“2020 PSU’s) to not be achieved, which are based on the achievement of certain free cash flow targets before cash tax and interest payments, subject to certain discretionary adjustments by the Board, over the three-year performance periods of 2019 through 2021 and 2020 through 2022, respectively. As such, during the six months ended June 30, 2020, the Company reversed $1.4 million of compensation expense related to the 2019 PSU’s. In addition, during the six months

ended June 30, 2020, the Company reversed $1.8 million of compensation expense related to the PSU awards granted in 2018 (“2018 PSU’s”), as the targets were not expected to be achieved as of June 30, 2020; however, during December 2020, the Compensation Committee of the Board modified the performance target for the 2018 PSU’s, as well as evaluated qualitative performance factors for the Company for 2020, which resulted in achievement of 95% of the target. The 2018 PSU’s vested as of December 31, 2020.

Nonvested PSU’s as of June 30, 2021, and changes during the year ended June 30, 2021 (unaudited) were as follows:

	Shares			Weighted Average Grant-Date Fair Value
Nonvested as of December 31, 2020		200,218		$	35.27
Granted		50,868			34.97
Forfeited		(3,375	)		35.96
Nonvested as of June 30, 2021		247,711		$	35.20

The Company's stock-based compensation expense (net reduction of expense) related to PSU’s during the three and six months ended June 30, 2021 and 2020 (unaudited), respectively, which is included in General and administrative expenses within the Condensed Consolidated Statements of Income (Loss), was as follows:

	Three Months Ended				Six Months Ended
(millions)	June 30, 2021		June 30, 2020		June 30, 2021		June 30, 2020
Stock-based compensation expense	$	0.3	$	0.1	$	0.4	$	(3.1	)

As of June 30, 2021, there was $3.1 million of unrecognized compensation costs related to PSU awards that are expected to be recognized over a weighted average remaining period of approximately 2.4 years. Since the Company no longer expects the required performance targets to be achieved for the 2019 and 2020 PSU’s, no future compensation expense is expected to be recognized; however, future compensation expense for the 2019 and 2020 PSU’s could reach a maximum of $14.1 million if certain performance targets are achieved.