We use share-based payments to compensate employees and non-employee directors. We recognize the cost of share-based payments under the fair-value-based method. Outstanding share-based awards include equity instruments in the form of stock options or restricted stock units that have included service conditions and, in certain cases, performance conditions. Our share-based awards also include share-settled performance unit awards. Share-settled performance unit awards are accounted for as equity awards. In 2020, we granted performance-based cash-settled phantom units, which are accounted for as a liability classified award. We issue shares of common stock when vested stock options are exercised, when restricted stock is granted and when restricted stock units and share-settled performance unit awards vest.

Stock Options — We estimate the grant date fair values of stock options using the Black-Scholes-Merton valuation model. Volatility assumptions are based on the historic volatility of our common stock over the most recent period equal to the expected term of the options as of the date such options are granted. The expected term assumptions are based on our experience with respect to employee stock option activity. Dividend yield assumptions are based on the expected dividends at the time the options are granted. The risk-free interest rate assumptions are determined by reference to United States Treasury yields. No options were granted during the nine months ended September 30, 2022 or 2021.

Stock option activity from January 1, 2022 to September 30, 2022 follows:


				Weighted
				Average
	Underlying			Exercise Price
	Shares			Per Share
Outstanding at January 1, 2022		3,720,150		$	20.93
Exercised		(640,000	)	$	16.20
Expired		(135,000	)	$	17.00
Outstanding at September 30, 2022		2,945,150		$	22.14
Exercisable at September 30, 2022		2,945,150		$	22.14

Restricted Stock Units — For all restricted stock unit awards made to date, shares of common stock are not issued until the units vest. Restricted stock units are subject to forfeiture for failure to fulfill service conditions and, in certain cases, performance conditions. Forfeitable dividend equivalents are accrued on certain restricted stock units that will be paid upon vesting. We use the straight-line method to recognize periodic compensation cost over the vesting period.

Restricted stock unit activity from January 1, 2022 to September 30, 2022 follows:


						Weighted
						Average Grant
	Time			Performance		Date Fair Value
	Based			Based		Per Share
Non-vested restricted stock units outstanding at January 1, 2022		3,044,719			359,315	$	8.31
Granted		1,554,849			—	$	17.37
Vested		(1,437,286	)		—	$	7.32
Forfeited		(57,668	)		—	$	12.90
Non-vested restricted stock units outstanding at September 30, 2022		3,104,614			359,315	$	12.71

As of September 30, 2022, we had unrecognized compensation cost related to our unvested restricted stock units totaling $30.1 million. The weighted-average remaining vesting period for these unvested restricted stock units was 1.65 years.

Performance Unit Awards — We have granted share-settled performance unit awards to certain employees (the “Performance Units”) on an annual basis since 2010. The Performance Units provide for the recipients to receive a grant of shares of common stock upon the achievement of certain performance goals during a specified period established by the Compensation Committee. The performance period for the Performance Units is generally the three-year period commencing on April 1 of the year of grant.

The performance goals for the Performance Units are tied to our total shareholder return for the performance period as compared to total shareholder return for a peer group determined by the Compensation Committee. For the performance units granted in April 2022 and April 2021, the peer group includes one market index and three market indices, respectively. The performance goals are considered to be market conditions under the relevant accounting standards and the market conditions were factored into the determination of the fair value of the respective Performance Units. For the Performance Units granted beginning in April 2019, the recipients will receive the target number of shares if our total shareholder return during the performance period, when compared to the peer group, is at the 55th percentile. If our total shareholder return during the performance period, when compared to the peer group, is at the 75th percentile or higher, then the recipients will receive two times the target number of shares. If our total shareholder return during the performance period, when compared to the peer group, is at the 25th percentile, then the recipients will only receive one-half of the target number of shares. If our total shareholder return during the performance period, when compared to the peer group, is between the 25th and 55th percentile, or the 55th and 75th percentile, then the shares to be received by the recipients will be determined using linear interpolation for levels of achievement between these points.

For the Performance Units granted beginning in April 2019, the payout shall not exceed the target number of shares if our total shareholder return is negative or zero. Additionally, the Performance Units granted in April 2020 will not pay out if our total shareholder return is not equal to or greater than the total stockholder return of the S&P 500 Index for the performance period.

The total target number of shares with respect to the Performance Units for the awards granted in 2018-2022 is set forth below:


	2022		2021		2020		2019		2018
	Performance		Performance		Performance		Performance		Performance
	Unit Awards		Unit Awards		Unit Awards		Unit Awards		Unit Awards
Target number of shares		414,000		843,000		500,500		489,800		310,700

In April 2021, 621,400 shares were issued to settle the 2018 Performance Units. In April 2022, 979,600 shares were issued to settle the 2019 Performance Units. The Performance Units granted in 2020, 2021 and 2022 have not reached the end of their respective performance periods.

Because the Performance Units are share-settled awards, they are accounted for as equity awards and measured at fair value on the date of grant using a Monte Carlo simulation model. The fair value of the Performance Units is set forth below (in thousands):


	2022		2021		2020		2019		2018
	Performance		Performance		Performance		Performance		Performance
	Unit Awards		Unit Awards		Unit Awards		Unit Awards		Unit Awards
Aggregate fair value at date of grant	$	10,743	$	7,225	$	826	$	9,958	$	8,004

These fair value amounts are charged to expense on a straight-line basis over the performance period. Compensation expense associated with the Performance Units is shown below (in thousands):


	2022		2021		2020		2019		2018
	Performance		Performance		Performance		Performance		Performance
	Unit Awards		Unit Awards		Unit Awards		Unit Awards		Unit Awards
Three months ended September 30, 2022	$	895	$	602	$	69	NA		NA
Three months ended September 30, 2021	NA		$	602	$	69	$	830	NA
Nine months ended September 30, 2022	$	1,791	$	1,806	$	206	$	830	NA
Nine months ended September 30, 2021	NA		$	1,204	$	206	$	2,489	$	667

As of September 30, 2022, we had unrecognized compensation cost related to our unvested Performance Units totaling $12.7 million. The weighted-average remaining vesting period for these unvested Performance Units was 1.45 years.

Phantom Units — In May 2020, the Compensation Committee approved a grant of long-term performance-based phantom units to our Chief Executive Officer and President, William A. Hendricks, Jr (the “Phantom Units”). The Phantom Units were granted outside of the 2014 Plan. Pursuant to this phantom unit grant, Mr. Hendricks may earn from 0% to 200% of a target award of 298,500 phantom units based on our achievement of the same performance conditions over the same performance period that applies to the Performance Units granted in April 2020, as described above. Earned Phantom Units, if any, will be settled in 2023, following completion of the three-year performance period, in a cash payment equal to the number of earned phantom units multiplied by our average trading price per share over the twenty consecutive trading days ending March 31, 2023. Because the Phantom Units are cash-settled awards, they are accounted for as a liability classified award. The grant date fair value of the Phantom Units was $1.2 million. Compensation expense is recognized on a straight-line basis over the performance period, with the amount recognized fluctuating as a result of the Phantom Units being remeasured to fair value at the end of each reporting period due to their liability-award classification. We recognized a $1.4 million and $0.2 million decrease to compensation expense associated with the Phantom Units during the three months ended September 30, 2022 and 2021, respectively, due to a decrease in fair value during the periods. We recognized $2.3 million and $1.3 million of compensation expense for the nine months ended September 30, 2022 and 2021, respectively.