Share-based Compensation (Details) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs, Capitalized Amount	$ 1,600,000	$ 1,500,000
Stock options
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]
Dividend yield (as a percent)	2.50%		2.37%
Expected life of option (in years)	4 years 9 months 22 days		3 years 8 months 15 days
Risk-free interest rate (as a percent)	1.82%		1.57%
Expected stock price volatility (as a percent)	31.00%		26.76%
Options Outstanding
Balance at beginning of period (in shares)	1,737,213	1,595,007	1,595,007
Granted (in shares)	60,000		445,100
Exercised (in shares)	(104,151)		(192,875)
Lapsed or cancelled (in shares)	(25,201)		(110,019)
Balance at end of period (in shares)	1,667,861		1,737,213
Options exercisable at end of period (in shares)	889,076		748,617
Weighted average fair value of options granted during the period	$ 1,496,838		$ 8,363,036
Weighted Average Exercise Price
Balance at beginning of year (in dollars per share)	$ 98.44	$ 95.52	$ 95.52
Granted (in dollars per share)	106.05		105.86
Exercised (in dollars per share)	84.03		76.90
Lapsed or cancelled (in dollars per share)	127.28		123.86
Balance at end of period (in dollars per share)	99.18		98.44
Options exercisable at end of period (in dollars per share)	$ 90.92		$ 87.72
Summary of restricted stock
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized	$ 12,600,000
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition	2 years
Restricted Stock Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value	$ 8,000,000		$ 7,600,000
Options Outstanding
Weighted average fair value of options granted during the period	$ 0	$ 10,650,077
Summary of restricted stock
Balance at beginning of year (in shares)	3,202,031	3,137,881	3,137,881
Granted (in shares)	0	98,800
Cancelled (in shares)	0	(34,650)
Balance at end of period (in shares)	3,202,031		3,202,031
Vested during the period (in shares)	82,786	83,822
Compensation expense recorded	$ 2,380,926	$ 7,153,966
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized	$ 18,400,000
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition	2 years 1 month
Long Term Incentive Plan Units [Member]
Options Outstanding
Weighted average fair value of options granted during the period	$ 20,500,000		$ 25,400,000
Performance Shares [Member]
Summary of restricted stock
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized	$ 12,100,000
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition	1 year 5 months
Share-based Compensation	$ 10,000,000	9,500,000
Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common Stock, Shares Held in Employee Trust, Shares	97,446
Long Term Outperformance Compensation Program 2014 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs, Capitalized Amount	$ 29,200,000
Summary of restricted stock
Compensation expense recorded	$ 2,100,000	$ 1,500,000