Stock Based Compensation

12 Months Ended

Dec. 31, 2020

Share-based Payment Arrangement [Abstract]

The Company accounts for stock-based compensation pursuant to relevant authoritative guidance, which requires measurement of compensation cost for all stock awards at fair value on the date of grant and recognition of compensation, net of estimated forfeitures, over the requisite service period for awards expected to vest. The Company has a Stock Incentive Plan (the "Plan"), pursuant to which permit the Company's board of directors grants equity to employees and directors. Under the Plan, a maximum of 16.75 million shares of our common stock is approved to be issued for grants of restricted stock and stock options. At December 31, 2020, there were 2.5 million shares available to be granted under the Plan.

The table below summarizes the expense recognized within general and administrative expenses in the Consolidated Statements of Income related to share-based payments recognized for the years ended December 31 (in thousands):


	2020		2019		2018
Stock options	$	23,407	$	32,736	$	43,443
Restricted stock	19,977		28,217		26,496
Stock-based compensation	$	43,384	$	60,953	$	69,939

The tax benefits recorded on stock based compensation expense and upon the exercises of options were $70.6 million, $61.6 million and $37.3 million for the years ended December 31, 2020, 2019 and 2018, respectively.

The following table summarizes the Company’s total unrecognized compensation cost related to stock-based compensation as of December 31, 2020 (cost in thousands):


	Unrecognized Compensation Cost		Weighted Average Period of Expense Recognition (in Years)
Stock options	$	35,286	2.30
Restricted stock	26,948		1.97
Total	$	62,234

Stock Options

The following summarizes the changes in the number of shares of common stock under option for the following periods (shares and aggregate intrinsic value in thousands):


	Shares	Weighted Average Exercise Price		Options Exercisable at End of Year	Weighted Average Exercise Price of Exercisable Options		Weighted Average Fair Value of Options Granted During the Year		Aggregate Intrinsic Value
Outstanding at December 31, 2017	8,031	$	109.78	4,029	$	75.80			$	663,815
Granted	412	204.59					$	50.07
Exercised	(708)	73.26							79,588
Forfeited	(119)	155.41
Outstanding at December 31, 2018	7,616	117.58		5,174	98.39				518,954
Granted	431	244.35					$	57.99
Exercised	(1,482)	115.53							255,242
Forfeited	(302)	167.35
Outstanding at December 31, 2019	6,263	124.38		5,137	109.03				1,022,860
Granted	503	215.36					$	53.18
Exercised	(1,681)	80.84							322,823
Forfeited	(121)	194.61
Outstanding at December 31, 2020	4,964	$	146.69	3,994	$	130.37			$	626,107
Expected to vest at December 31, 2020	970	$	213.89

The following table summarizes information about stock options outstanding at December 31, 2020 (shares in thousands):


Exercise Price	Options Outstanding	Weighted Average Remaining Vesting Life in Years	Options Exercisable
$10.00 – $150.74	3,541	0.01	3,488
$151.49 – $165.96	242	0.27	190
$172.68 – $199.75	495	1.60	198
$202.02 – $209.05	45	1.54	14
$213.69 – $231.70	351	2.83	37
$248.28 – $263.21	271	2.08	64
$288.37 – $319.55	19	2.63	3
	4,964		3,994

The aggregate intrinsic value of stock options exercisable at December 31, 2020 was $569.0 million. The weighted average remaining contractual term of options exercisable at December 31, 2020 was 4.8 years.

The fair value of stock option awards granted was estimated using the Black-Scholes option pricing model with the following weighted-average assumptions for grants or modifications during the years ended December 31 as follows:


	2020		2019		2018
Risk-free interest rate	0.37	%	2.40	%	2.57	%
Dividend yield	—		—		—
Expected volatility	31.00	%	26.40	%	26.92	%
Expected life (in years)	3.9		3.7		3.8

The weighted-average remaining contractual life for options outstanding was 5.3 years at December 31, 2020.

Restricted Stock

The fair value of restricted stock units granted with market based vesting conditions was estimated using the Monte Carlo simulation valuation model with the following assumptions during 2019. There were no restricted stock shares granted with market based vesting conditions in 2020 and 2018.


	2019
Risk-free interest rate	1.48	%
Dividend yield	—
Expected volatility	25.40	%
Expected life (in years)	2.36

The following table summarizes the changes in the number of shares of restricted stock and restricted stock units for the following periods (shares in thousands):


	Shares	Weighted Average Grant Date Fair Value
Outstanding at December 31, 2017	365	$	155.58
Granted	107	200.71
Cancelled	(47)	339.34
Issued	(251)	154.85
Outstanding at December 31, 2018	174	190.73
Granted	232	212.79
Cancelled	(49)	225.96
Issued	(114)	206.05
Outstanding at December 31, 2019	243	246.34
Granted	171	252.36
Cancelled	(100)	249.17
Issued	(140)	227.20
Outstanding at December 31, 2020	174	$	265.29