Options are exercisable once vested. Options are exercisable at such times and subject to such terms as determined by the Compensation Committee, but under no circumstances may be exercised if such exercise would cause a violation of the ownership limit in the Company’s charter. Options expire 10 years from the date of grant. Beginning in 2017, the CNG Committee decided to the replace stock options granted to executives with performance based stock units for executive compensation. See the "Performance-Based Stock Units" section below.

Also as defined under the terms of the Plan, restricted stock grants may be awarded. The stock grants are subject to a vesting period over which the restrictions are released and the stock certificates are given to the grantee. During the vesting period, the grantee is not permitted to sell, transfer, pledge, encumber or assign shares of restricted stock granted under the Plan; however, the grantee has the ability to vote the shares and receive nonforfeitable dividends paid on shares. Unless otherwise determined by the Compensation Committee at the time of grant, the forfeiture and transfer restrictions on the shares lapse over a four-year period beginning on the date of grant. For actions taken prior to July 2020, references to the Compensation Committee refer to its predecessor, the CNG Committee; the Board split the CNG Committee into two committees, the Compensation Committee and the Nominating and Governance Committee, effective July 1, 2020.

A summary of stock option activity is as follows:


Options	Number of Shares	Weighted Average Exercise Price		Weighted Average Remaining Contractual Life (Years)	Aggregate Intrinsic Value as of December 31, 2021
Outstanding at December 31, 2018	417,581	$	31.58

Exercised	(211,057)	14.65

Outstanding at December 31, 2019	206,524	$	48.88

Exercised	(134,930)	35.26

Outstanding at December 31, 2020	71,594	$	74.54

Exercised	(62,322)	73.36

Outstanding at December 31, 2021	9,272	$	82.47	3.98	$1,338

Vested	9,272	$	82.47	3.98	$1,338
Ending Exercisable	9,272	$	82.47	3.98	$1,338

The aggregate intrinsic value in the table above represents the total value (the difference between the Company’s closing stock price on the last trading day of 2021 and the exercise price, multiplied by the number of in-the-money options) that would

have been received by the option holders had all option holders exercised their options on December 31, 2021. The amount of aggregate intrinsic value will change based on the fair market value of the Company’s stock. The total intrinsic value of options exercised for the years ended December 31, 2021, 2020 and 2019 was $3,925, $10,016 and $18,089, respectively.

There have been no options granted since 2016. The fair value of each option grant was estimated on the date of grant using the Black-Scholes option-pricing model. The Black-Scholes model incorporates assumptions to value stock-based awards. The risk-free rate is based on the U.S. Treasury yield curve in effect at the time of the grant for the estimated life of the option. The Company uses actual historical data to calculate the expected price volatility, dividend yield and average expected term. The forfeiture rate, which is estimated at a weighted-average of 4.6% of unvested options outstanding as of December 31, 2021, is adjusted periodically based on the extent to which actual forfeitures differ, or are expected to differ, from the previous estimates.


	Options Outstanding				Options Exercisable
Exercise Price	Shares	Weighted Average Remaining Contractual Life	Weighted Average Exercise Price		Shares	Weighted Average Exercise Price
$65.36 - $65.36	1,582	3.15	$	65.36	1,582	$	65.36
$85.99 - $85.99	7,690	4.15	85.99		7,690	85.99

The Company recorded compensation expense relating to outstanding options of $0, $27 and $364 in general and administrative expense for the years ended December 31, 2021, 2020 and 2019, respectively. Net proceeds received for the years ended December 31, 2021, 2020 and 2019, related to option exercises was $4,572, $4,759 and $3,063, respectively. At December 31, 2021, there was no unrecognized compensation expense related to non-vested stock options under the Plan.

The Company recorded $9,260, $9,244 and $9,173 of expense in general and administrative expense in its statement of operations related to restricted stock awards granted to employees and directors for the years ended December 31, 2021, 2020 and 2019, respectively. The forfeiture rate, which is estimated at a weighted-average of 10.0% of unvested awards outstanding as of December 31, 2021, is adjusted periodically based on the extent to which actual forfeitures differ, or are expected to differ, from the previous estimates. At December 31, 2021 there was $13,843 of total unrecognized compensation expense related to non-vested restricted stock awards under the Plan. That cost is expected to be recognized over a weighted-average period of 2.15 years. The fair value of common stock awards is determined based on the closing trading price of the Company’s common stock on the grant date.


Restricted Stock Grants	Shares	Weighted-Average Grant-Date Fair Value
Unreleased at December 31, 2018	223,114	$	80.02
Granted	109,081	101.52
Released	(110,724)	79.58
Cancelled	(8,863)	90.11
Unreleased at December 31, 2019	212,608	$	91.62
Granted	95,671	98.81
Released	(94,164)	89.43
Cancelled	(5,083)	93.16
Unreleased at December 31, 2020	209,032	$	95.86
Granted	99,802	132.75
Released	(96,248)	91.65
Cancelled	(12,808)	113.89
Unreleased at December 31, 2021	199,778	$	115.16

The performance-based stock units (the "PSUs") granted to executives represent the right to earn shares of the Company's common stock. These awards have two financial performance components: (1) the Company's core FFO performance ("FFO Target"), and (2) the Company's total stockholder return relative to the performance of a defined group of peers ("TSR Target"). Each of these performance components are weighted 50% and are measured over the performance period, which is defined as the three-year period ending December 31 from the year of grant. At the end of the performance period, the financial performance components are reviewed to determine the number of shares actually granted to executives, which can be as low as zero shares and up to a maximum of two shares issued for each PSU. A summary of the PSU activity is as follows:


Performance-Based Stock Units	Units	Weighted-Average Grant-Date Fair Value
Unvested at December 31, 2018	58,806	$	89.87
Granted	49,334	103.18
Unvested at December 31, 2019	108,140	$	95.94
Granted	45,242	129.38
Released	(30,071)	$	112.16
Unvested at December 31, 2020	123,311	$	104.25
Granted	40,832	138.04
Released	(28,735)	$	117.19
Unvested at December 31, 2021	135,408	$	111.69

The Company recorded $8,043, $7,048 and $3,514 of expense in general and administrative expense in its statement of operations related to PSUs granted to employees for the years ended December 31, 2021, 2020 and 2019, respectively. The Company estimated the fair value of the PSUs as of the grant date, using the closing trading price of the Company's common stock on the grant date to value the FFO Target portion. A Monte Carlo simulation model was used to calculate the fair value of the TSR Target portion of the PSUs, using the following assumptions:


	For the Year Ended December 31,
	2021	2020	2019
Intrinsic value	$30,701	$12,266	$6,211
Risk-free rate	0.22%	1.42%	2.53%
Volatility	28.5%	18.4%	20.7%
Expected term (in years)	2.9	2.9	2.8
Dividend yield	—%	—%	—%
Unrecognized compensation cost	$8,859	$6,406	$4,315
Term over which compensation cost recognized (in years)	3	3	3

Under the terms of the PSUs, dividends for the entire measurement period are paid in cash when the shares are released, so a dividend yield of zero was used. The valuation model applied in this calculation utilizes subjective assumptions that could potentially change over time, including the probabilities associated with achieving the FFO Targets (categorized within Level 3 of the fair value hierarchy). Therefore, the amount of unrecognized compensation expense at December 31, 2021 noted above does not necessarily represent the expense that will ultimately be realized by the Company in the statement of operations.