The Company measures stock-based compensation expense at the grant date, based on the estimated fair value of the award based on assumptions as of the grant date. The expense is recognized on a straight-line basis over the requisite employee service period or performance period (generally the vesting period) for awards expected to vest. For those awards in which there is no requisite service period, the Company immediately recognizes the compensation expense. If the award is later modified, the Company may measure the award based on the estimated fair value at the modification date and recognize expense over the remaining requisite employee service period or performance period. The Company accounts for forfeitures of stock-based awards as they occur.

The Company has an amended and restated long-term incentive plan (the "Plan") under which the Company may grant future awards. On March 7, 2018, the Company’s Board of Directors (the “Board”) approved an amendment to the Plan that increased the number of shares of common stock available under the Plan from 2,975,000 to 3,775,000. Company stockholders approved the Plan amendment on May 8, 2018. Forfeited and expired options under the Plan become generally available for reissuance. At December 31, 2020, 647,903 shares remained available for grant under the Plan.

Stock-based compensation expense related to vested stock grants are included in General and administrative expenses within the Consolidated Statements of (Loss) Income. The Company’s authorized vested stock grants to certain directors and related expense for the years ended December 31, 2020, 2019 and 2018, was as follows:

	Year Ended December 31,
(millions, except stock grants)	2020		2019		2018
Vested stock grants		25,066		14,076		12,736
Stock-based compensation expense	$	0.5	$	0.5	$	0.5

During the year ended December 31, 2019, the Company granted of 37,235 restricted stock units to certain executives that vest over three years from the grant date.

During the year ended December 31, 2018, the Company granted of 48,663 and 8,426 restricted stock units to certain executives that vest over three years and five years from the grant date, respectively.

Nonvested restricted stock units as of December 31, 2020, and changes during the year ended December 31, 2020 were as follows:

	Shares			Weighted Average Grant-Date Fair Value
Nonvested as of December 31, 2019		153,442		$	27.46
Granted		—			—
Vested		(102,166	)		24.56
Forfeited		—			—
Nonvested as of December 31, 2020		51,276		$	33.24

The Company's stock-based compensation expense related to the restricted stock units for the years ended December 31, 2020, 2019 and 2018, which is included in General and administrative expenses within the Consolidated Statements of (Loss) Income, was as follows:

	Year Ended December 31,
(millions)	2020		2019		2018
Stock-based compensation expense	$	1.1	$	1.1	$	0.9

Unrecognized stock-based compensation expense related to restricted stock units and the respective weighted average periods in which the expense will be recognized as of December 31, 2020 was as follows:

	Year Ended December 31,
(millions)	2020
Unrecognized stock-based compensation	$	0.6
Weighted average (years)	1.2 years

In September 2014, the Board authorized a performance-based incentive program under the Plan (“Performance-based Incentive Program”), whereby the Company may issue PSU’s to certain individuals that represent shares potentially issuable in the future. The objective of the Performance-Based Incentive Program is to link compensation to business performance, encourage the ownership of the Company’s common stock, retain key employees and reward management’s performance. The Performance-Based Incentive Program provides participants with the opportunity to earn vested common stock if certain performance targets for pre-tax cash flow are achieved over the cumulative three-year period starting in the year of grant and the participants satisfy service-based vesting requirements. The stock-based compensation expense associated with nonvested PSU’s is recognized on a straight-line basis over the shorter of the vesting period or minimum service period and dependent upon the probable outcome of the number of shares that will ultimately be issued based on the achievement of pre-tax cash flow over the cumulative three-year period.

The Company granted awards during the years ended December 31, 2020, 2019 and 2018 of 96,056, 125,232 and 100,715, respectively, under the Performance-Based Incentive Program. The performance target is based on the achievement of free cash flow before cash taxes and interest payments over the cumulative three-year period starting in the year of grant, subject to certain discretionary adjustments by the Board. 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 awards granted in 2020 (“2020 PSU’s) and 2019 (“2019 PSU’s), are 181,504 and 227,478, respectively.

Due to the impact of COVID-19 on the Company’s operations, during the year ended December 31, 2020, the Compensation Committee of the Board modified the performance target for the awards granted in 2018 (“2018 PSU’s”), as well as evaluated qualitative performance factors for the Company during 2020, which resulted in achievement of 95% of the target for the 2018 PSU’s. The 2018 PSU’s vested as of December 31, 2020. The Company concluded this determination was a Type III modification and compensation expense was recorded based on the fair value of the awards at the date of modification. Had the Compensation Committee not made this determination, the Company would have recorded no compensation expense related to the 2018 PSU’s. The performance targets for the 2019 and 2020 PSU’s have not been amended. As such, during the year ended December 31, 2020, $1.4 million of compensation expense related to the

2019 PSU’s was reversed, since the Company no longer expected the required performance targets to be achieved. In addition, the Company has not recorded compensation expense related to the 2020 PSU’s.

Nonvested PSU’s as of December 31, 2020, and changes during the year ended December 31, 2020 was as follows:

	Shares			Weighted Average Grant-Date Fair Value
Nonvested as of December 31, 2019		212,096		$	35.01
Granted		96,056			37.89
Vested		(81,115	)		30.01
Forfeited		(23,173	)		36.27
Expired		(3,646	)		37.59
Nonvested as of December 31, 2020		200,218		$	35.27

The Company's stock-based compensation expense (net reduction of expense) related to PSU’s during the years ended December 31, 2020, 2019 and 2018, which is included in General and administrative expenses within the Consolidated Statements of (Loss) Income, was as follows:

	Year Ended December 31,
(millions)	2020			2019		2018
Stock-based compensation expense	$	(1.0	)	$	3.3	$	1.4

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.