Stock Based Compensation (Tables)

12 Months Ended

Dec. 31, 2020

Share-based Payment Arrangement [Abstract]

Summary of Expense Related to Share-Based Payments

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

Summary of Total Unrecognized Compensation Cost Related to Stock-Based Compensation

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

Summary of Changes in Number of Shares of Common Stock Under Option

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

Schedule of Stock Options Exercise Price

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

Schedule of Weighted-Average Assumptions

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

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

Summary of Changes in Number of Shares of Restricted Stock and Restricted Stock Units

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