Stock Based Compensation (Tables)

12 Months Ended

Dec. 31, 2017

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):

	2017		2016		2015
Stock options	$	56,400	$	35,234	$	44,260
Restricted stock	36,897		28,712		45,862
Stock-based compensation	$	93,297	$	63,946	$	90,122

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, 2017 (cost in thousands):

	Unrecognized Compensation Cost		Weighted Average Period of Expense Recognition (in Years)
Stock options	$	84,452	1.33
Restricted stock	18,819		1.06
Total	$	103,271

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, 2014	5,131		$	58.71	2,370	$	21.75			$	461,770
Granted	654		154.56					$	35.32
Exercised	(586	)	33.97							63,863
Forfeited	(196	)	95.16
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
Expected to vest at December 31, 2017	8,031		$	109.78

Schedule of Stock Options Exercise Price

The following table summarizes information about stock options outstanding at December 31, 2017 (shares in thousands):

Exercise Price	Options Outstanding	Weighted Average Remaining Vesting Life in Years	Options Exercisable
$10.00 – 58.02	2,218	0.00	2,218
74.99 – 111.09	104	0.03	90
114.90 – 138.47	2,029	0.77	577
140.23-150.74	2,593	1.60	906
151.16-158.24	618	1.48	195
165.96-174.35	469	3.08	43
	8,031		4,029

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:

	2017		2016		2015
Risk-free interest rate	1.65	%	1.08	%	1.47	%
Dividend yield	—		—		—
Expected volatility	28.00	%	27.29	%	27.77	%
Expected life (in years)	3.4		3.5		4.5

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, 2014	716		$	121.38
Granted	126		151.33
Cancelled	(52	)	135.92
Issued	(293	)	85.40
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