The Company has a defined contribution plan covering all eligible employees. Under the plan, employees may contribute up to 90 percent of their eligible annual compensation with the Company making matching contributions on employee deferrals of up to 5 percent of eligible employee wages. The matching contributions on pilot deferrals is 10 percent of eligible wages resulting from the pilot collective bargaining agreement.

The Company recognized expense under this plan of $18.6 million, $19.0 million, and $19.1 million for the years ended December 31, 2020, 2019 and 2018, respectively.

The Company reserved 2,000,000 shares of common stock for the Company to grant stock options, restricted stock, cash-settled stock appreciation rights ("SARs") and other stock-based awards to certain officers, directors and employees of the Company under the 2016 Long-Term Incentive Plan (the "2016 Plan"). The 2016 Plan is administered by the Company’s compensation committee of the Board of Directors.

The Company reserved 1,000,000 shares of common stock for employee purchases under the 2014 Employee Stock Purchase Plan ("ESPP"). Shares are purchased semi-annually, at a discount, based on the market value at period-end. Employees may contribute up to 25 percent of their base pay per offering period, not to exceed $25,000 each calendar year, for the purchase of common stock. The ESPP is a compensatory plan under applicable accounting guidance and results in the recognition of compensation expense.


	Total number of shares purchased in year	Average price paid per share		Weighted-average fair value of discount under the ESPP (1)
As of December 31, 2018	33,300	$	134.31	$	16.79
As of December 31, 2019	38,464	$	133.54	$	23.51
As of December 31, 2020	56,866	$	90.63	$	14.10

(1) The weighted-average fair value of the discount under the ESPP granted is equal to a percentage discount from the market value of the common stock at the end of each semi-annual purchase period. The Company increased the discount from 10 percent to 15 percent for the second offering period of 2018. 15 percent is the maximum allowable discount under the ESPP.

For the years ended December 31, 2020, 2019 and 2018, the Company recorded compensation expense of $20.1 million, $19.2 million and $15.6 million, respectively, related to restricted stock, stock options, cash-settled SARs and the ESPP. Forfeiture rates are estimated at the time of grant based on historical actuals for similar grants, and are matched to actuals over the vesting period.

The unrecognized compensation cost was $27.5 million as of December 31, 2020 for unvested restricted stock expected to be recognized over a weighted-average period of 1.34 years. As of December 31, 2020, there was no unrecognized compensation cost for either cash-settled SARs or stock options.

The fair value of stock options granted is estimated as of the grant date using the Black-Scholes option pricing model. The contractual terms of the Company’s stock option awards granted range from five to ten years. A summary of option activity as of December 31, 2020, 2019 and 2018, and changes during the years then ended, is presented below:


	Options	Weighted Average Exercise Price		Weighted Average Remaining Contractual Life (years)	Aggregate Intrinsic Value (thousands)
Outstanding at December 31, 2017	27,575	$	97.88	0.72	$	1,568
Exercised	(17,838)	92.04
Outstanding at December 31, 2018	9,737	$	108.59	0.18	$	—
Exercised	(9,737)	108.59
Outstanding at December 31, 2019	—	$	—	0.00	$	—
Exercised	—	—
Outstanding at December 31, 2020	—	$	—	0.00	$	—

During the years ended December 31, 2020, 2019 and 2018, the total intrinsic value of options exercised was $0.0 million, $0.2 million and $1.4 million, respectively. Cash received from option exercises for the years ended December 31, 2020, 2019 and 2018 was $0.0 million, $1.1 million and $1.6 million, respectively.

The closing price of the Company's stock on the date of grant is used as the fair value for the issuance of restricted stock. A summary of the status of non-vested restricted stock grants during the years ended December 31, 2020, 2019 and 2018 is presented below:


	Shares	Weighted Average Grant Date Fair Value Per Share
Non-vested at December 31, 2017	192,890	$	153.32
Granted	102,842	155.02
Vested	(85,410)	153.85
Forfeited	(14,128)	154.65
Non-vested at December 31, 2018	196,194	$	153.88
Granted	218,477	143.72
Vested	(104,816)	152.07
Forfeited	(15,047)	148.97
Non-vested at December 31, 2019	294,808	$	147.25
Granted	267,169	137.80
Vested	(291,303)	147.58
Forfeited	(5,147)	145.82
Non-vested at December 31, 2020	265,527	$	142.25

The total fair value of restricted stock that vested during the years ended December 31, 2020, 2019 and 2018 was $43.0 million, $15.9 million and $13.4 million, respectively.

Cash-settled SARs are liability classified awards for which the fair value and compensation expense recognized are updated monthly using the Black-Scholes option pricing model.

The following range of assumptions in the Black-Scholes pricing model was used to determine fair value as of December 31 of the years indicated below (all cash-settled SARs were fully vested as of December 31, 2019):


	2020		2019		2018
Weighted-average volatility	—	%	—	%	35.0	%
Expected term (in years)	N/A		N/A		0.8
Risk-free interest rate	—	%	—	%	2.6	%
Dividend yield	—	%	—	%	1.68	%

These rights were fully vested as of December 31, 2019. Expected volatilities used for award valuation are based on the historical volatility of the Company's common stock price.

Expected term represents the weighted average time between the award’s grant date and its expected exercise date. The Company estimated the expected term assumption in 2020, 2019 and 2018 using historical award exercise activity and employee termination activity.

The risk-free interest rate for periods equal to the expected term of an award is based on a blended historical rate using Federal Reserve rates for U.S. Treasury securities.

A summary of cash-settled SARs awards activity during the years ended December 31, 2020, 2019 and 2018 is presented below:


	# of SARs	Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (years)	Aggregate Intrinsic Value (thousands)
Balance at December 31, 2017	80,464	$	155.13

Forfeited	(12,890)	181.47
Exercised	(13,642)	98.37
Balance at December 31, 2018	53,932	$	163.19


Exercised	(9,886)	135.53
Balance at December 31, 2019	44,046	$	169.40

Forfeited	(29,046)	181.47
Exercised	(15,000)	186.85
Balance at December 31, 2020	—	$	—	0.00	$	—
Vested at December 31, 2020	—	$	—	0.00	$	—
Exercisable at December 31, 2020	—	$	—	0.00	$	—