Stock Based Compensation (Tables)

12 Months Ended

Dec. 31, 2018

Disclosure of Compensation Related Costs, Share-based Payments [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):

	2018		2017		2016
Stock options	$	43,443	$	56,400	$	35,234
Restricted stock	26,496		36,897		28,712
Stock-based compensation	$	69,939	$	93,297	$	63,946

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, 2018 (cost in thousands):

	Unrecognized Compensation Cost		Weighted Average Period of Expense Recognition (in Years)
Stock options	$	56,281	1.28
Restricted stock	4,400		0.45
Total	$	60,681

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, 2015	5,003		$	72.72	2,545	$	26.82			$	351,277
Granted	1,780		133.33					$	28.61
Exercised	(500	)	42.36							49,592
Forfeited	(137	)	140.67
Outstanding at December 31, 2016	6,146		91.20		3,429	55.00				309,238
Granted	2,885		145.35					$	32.57
Exercised	(633	)	71.43							76,546
Forfeited	(367	)	144.51
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
Expected to vest at December 31, 2018	7,616		$	117.58

Schedule of Stock Options Exercise Price

The following table summarizes information about stock options outstanding at December 31, 2018 (shares in thousands):

Exercise Price	Options Outstanding	Weighted Average Remaining Vesting Life in Years	Options Exercisable
$10.00 – $40.65	1,874	0.00	1,874
87.61 – 138.47	1,868	0.18	1,428
140.23 – 150.74	2,534	0.92	1,430
151.16 – 156.04	519	0.71	326
165.96 – 174.35	424	2.11	108
199.75 – 206.73	289	3.01	—
209.05 – 216.18	108	2.97	8
	7,616		5,174

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:

	2018		2017		2016
Risk-free interest rate	2.57	%	1.65	%	1.08	%
Dividend yield	—		—		—
Expected volatility	26.92	%	28.00	%	27.29	%
Expected life (in years)	3.8		3.4		3.5

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, 2015	497		$	149.40
Granted	152		128.90
Cancelled	(41	)	145.25
Issued	(229	)	151.72
Outstanding at December 31, 2016	379		140.39
Granted	238		141.99
Cancelled	(48	)	152.95
Issued	(204	)	136.85
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