Long-term Equity-based Compensation (Tables)

12 Months Ended

Dec. 31, 2018

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions

The assumptions used in the Black-Scholes pricing model for Tandem Awards granted during the years endedDecember 31, 2018, 2017 and 2016 are presented below.

	2018					2017					2016
RANGE OF VALUATION ASSUMPTIONS
Expected Volatility	27.31	%	-	32.15	%	26.17	%	-	30.39	%	25.85	%	-	42.19	%
Risk-free Interest Rate	2.44		-	3.00		1.59		-	2.25		0.77		-	2.01
Expected Dividend Yield	1.16		-	1.72		1.39		-	2.43		2.22		-	3.41
WEIGHTED-AVERAGE EXPECTED LIFE IN YEARS
Employee Grants	4		-	6		4		-	6.5		1		-	6.5
Director Grants	N/A					N/A					N/A

Disclosure of Share-based Compensation Arrangements by Share-based Payment Award

activity for the year endedDecember 31, 2018 is presented below.

	Shares Subject to Awards		Weighted- average Exercise Price Per Share ($)		Weighted- average Remaining Contractual Life (in Years)	Aggregate Intrinsic Value ($ In Millions)
Outstanding at Beginning of the Year	1,012,279		$	37.45
Granted	576,681		60.98
Exercised	(107,536	)	36.74
Forfeited or Expired	(47,151	)	52.06
Outstanding at December 31, 2018	1,434,273		46.48		7.86	$	28.8
Vested and Expected to Vest at December 31, 2018	1,359,250		$	46.22	7.82	$	27.7
Exercisable at December 31, 2018	586,600		$	36.18	6.71	$	17.7

Schedule of Options Outstanding

Information pertaining to Tandem Awards outstanding at December 31, 2018 is presented below.

					Outstanding				Exercisable
Range of Exercise Prices ($)					Shares Subject to Awards	Weighted- average Exercise Price Per Share ($)		Weighted- average Remaining Contractual Life (in Years)	Shares Subject to Awards	Weighted- average Exercise Price Per Share ($)
$	10.01	-	$	20.00	4,000	$	16.48	0.35	4,000	$	16.48
20.01		-	30.00		187,410	27.77		6.22	140,206	27.79
30.01		-	40.00		249,202	34.89		6.51	206,760	34.76
40.01		-	50.00		431,888	42.57		7.81	231,473	42.34
50.01		-	60.00		489,797	59.90		9.08	244	54.50
60.01		-	70.00		58,875	67.09		9.14	3,917	66.35
70.01		-	80.00		10,310	77.76		9.49	—	—
80.01		-	90.00		2,791	82.10		9.68	—	—
10.01		-	90.00		1,434,273	46.48		7.86	586,600	36.18

Schedule of Share-based Compensation, Nonemployee Director Deferred Stock Unit Award Plan, Activity [Table Text Block]

Activity related to DSU awards for the year endedDecember 31, 2018 is presented below.

	Number of DSUs	Weighted- average Grant-date Fair Value Per DSU
Vested Balance at Beginning of the Year	44,560	$	35.54
Granted and Vested	12,780	77.50
Vested Balance at December 31, 2018	57,340	$	44.89

Time Vested Restricted Stock [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Schedule of Share-based Compensation, Restricted Stock and Restricted Stock Units Activity

Activity related to nonvested RSUs for the year endedDecember 31, 2018 is presented below.

	Time-based Restricted Stock Unit Awards
	Number of Restricted Stock Units		Weighted- average Grant-date Fair Value Per Unit
Nonvested Balance at Beginning of the Year	130,247		$	40.34
Granted	249,422		73.94
Vested	(51,647	)	49.76
Forfeited	(11,781	)	38.71
Nonvested Balance at December 31, 2018	316,241		$	65.36

Performance Based Restricted Stock [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Schedule of Share-based Compensation, Restricted Stock and Restricted Stock Units Activity

Activity related to nonvested PSU awards for the year endedDecember 31, 2018 is presented below.

	PSU Awards
	Number of PSUs		Weighted- average Grant-date Fair Value Per PSU
Nonvested Balance at Beginning of the Year	225,983		$	36.90
Granted	191,292		56.88
Vested	(77,244	)	37.63
Forfeited	(12,731	)	47.71
Nonvested Balance at December 31, 2018	327,300		$	47.14