In June 2024, in connection with our stockholders’ approval at our 2024 annual meeting of stockholders, we adopted the 2024 Long Term Incentive Plan (the “2024 LTIP”), which provides for the issuance of restricted stock units, performance stock units, stock options, and various other forms of awards, and reserved 3,100,000 shares of common stock for issuance under the 2024 LTIP. The 2024 LTIP supersedes and replaces all of our previous long-term incentive plans (the “Prior Plans”), such that awards may not be granted under the Prior Plans subsequent to the adoption of the 2024 LTIP. Awards granted under the Prior Plans will remain subject to the terms and conditions set forth in the applicable Prior Plan. The Prior Plans and 2024 LTIP are collectively referred to herein as the “LTIP.”

We record compensation expense associated with the issuance of awards under the LTIP on a straight-line basis over the vesting period based on the fair value of the awards as of the date of grant within general and administrative expense in the accompanying consolidated statements of operations. The following table outlines the compensation expense recorded by type of award (in thousands):


	Year Ended December 31,
	2024		2023		2022
Restricted and deferred stock units	$	28,395	$	19,502	$	19,401
Performance stock units	19,877		15,429		11,966

Total stock-based compensation	$	48,272	$	34,931	$	31,367

As of December 31, 2024, unrecognized compensation expense related to the awards granted under the LTIP will be amortized through the relevant periods as follows (in thousands):


	Unrecognized Compensation Expense		Final Year of Recognition
Restricted and deferred stock units	$	34,232	2027
Performance stock units	22,877		2026
Total unrecognized stock-based compensation	$	57,109

We grant time-based restricted stock units (“RSUs”) to our officers, executives, and employees and time-based deferred stock units (“DSUs”) to our non-employee directors under the LTIP. Each RSU and DSU represents a right to receive one share of our common stock after the RSU or DSU vests and is settled. RSUs generally vest ratably either over a one, two, or three-year service period on each anniversary following the grant date. RSUs are settled in shares of our common stock shortly after vesting. DSUs generally vest over a one-year period following the grant date. DSUs are settled in shares of our common stock upon the non-employee director’s separation of service from our Board. The grant-date fair value of RSUs and DSUs is equal to the closing price of our common stock on the date of the grant.

The following table presents the changes in non-vested RSUs and DSUs for the year ended December 31, 2024:


	RSUs and DSUs	Weighted-Average Grant-Date Fair Value
Non-vested, beginning of year	855,627	$	66.31
Granted	477,506	64.30
Vested	(317,672)	64.94
Forfeited	(82,559)	66.89
Non-vested, end of year	932,902	$	65.69

We grant market-based performance stock units (“PSUs”) to our officers and certain executives under the LTIP. The number of shares of our common stock issued to settle PSUs ranges from zero to 225% (or, for PSUs granted prior to fiscal year 2023, 200%) of the number of PSUs granted and is determined based on performance achievement against certain market-based criteria over a three-year performance period. PSUs generally vest on December 31 of the year preceding the third anniversary of the date of grant and settle by March 15 of the following year upon the determination and approval of performance achievement by the Compensation Committee of our Board.

Performance achievement is determined based on either, or a combination of, (1) our annualized absolute total stockholder return (“TSR”) or (2) for certain PSUs granted prior to fiscal year 2023, our absolute TSR relative to that of a defined peer group. Absolute TSR is determined based upon the change in our stock price over the performance period plus dividends paid. For awards with a relative TSR component, our absolute TSR is compared with the absolute TSRs of a group of peer companies over the performance period.

The grant-date fair value of the PSUs was estimated using a Monte Carlo valuation model. The Monte Carlo valuation model is based on random projections of stock price paths and repeated numerous times to achieve a probabilistic assessment. Significant assumptions used in this valuation include our expected volatility as well as the volatilities for each of our peers and an interpolated risk-free interest rate based on U.S. Treasury yields with maturities consistent with the performance period.

The following table presents the change of non-vested PSUs for the year ended December 31, 2024:


	PSUs	Weighted-Average Grant-Date Fair Value
Non-vested, beginning of year	472,593	$	92.08
Granted(1)	270,509	74.55
Additional shares based on performance(2)	59,504	97.45
Vested(2)	(139,218)	91.59
Forfeited	(13,342)	99.71

Non-vested, end of year(1)	650,046	$	85.23

(1)The number of awards assumes that the associated performance condition is met at the target amount (multiplier of one). The final number of shares of our common stock issued may vary depending on the performance multiplier, which ranges from zero to 225% (or, for PSUs granted prior to fiscal year 2023, 200%), depending on the level of satisfaction of the performance condition.

(2)Upon completion of the performance period for the PSUs granted in 2021, a performance achievement of 200% or 141%, as applicable, was applied to each of the grants, resulting in a number of shares greater than the target amount of such PSUs vesting and being settled during the year ended December 31, 2024.

The aggregate grant-date fair value of the PSUs granted under the LTIP during the year ended December 31, 2024 was $20.2 million. The performance period for PSUs granted in 2022 ended on December 31, 2024. These PSUs are expected to be released during the first quarter of 2025 with a performance achievement of 46% or 54%, as applicable.

The following table presents the range of assumptions used to determine the fair value of the PSUs with market-based settlement criteria as granted under the LTIP throughout each of the periods presented:


	Year Ended December 31,
	2024	2023	2022
Expected term (in years)	3.0	3.0	3.2
Risk-free interest rate	4.5%	3.6% to 5.0%	1.8% to 3.2%
Expected daily volatility	3.0%	3.1% to 3.7%	4.0% to 4.7%