Share-based Compensation (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Stock options
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]
Dividend yield (as a percent)	2.37%	1.97%	1.60%
Expected life of option (in years)	3 years 8 months 12 days	3 years 7 months 6 days	3 years 7 months 6 days
Risk-free interest rate (as a percent)	1.57%	1.43%	1.29%
Expected stock price volatility (as a percent)	26.76%	32.34%	33.97%
Options Outstanding
Balance at beginning of year (in shares)	1,595,007	1,462,726	1,765,034
Granted (in shares)	445,100	389,836	102,050
Exercised (in shares)	(192,875)	(217,438)	(348,156)
Lapsed or cancelled (in shares)	(110,019)	(40,117)	(56,202)
Balance at end of period (in shares)	1,737,213	1,595,007	1,462,726
Options exercisable at end of period (in shares)	748,617	589,055	428,951
Weighted average fair value of options granted during the period	$ 8,363,036	$ 9,522,613	$ 2,841,678
Weighted Average Exercise Price
Balance at beginning of year (in dollars per share)	$ 95.52	$ 87.98	$ 83.24
Granted (in dollars per share)	105.86	112.54	119.12
Exercised (in dollars per share)	76.90	74.69	72.76
Lapsed or cancelled (in dollars per share)	123.86	98.61	90.03
Balance at end of period (in dollars per share)	98.44	95.52	87.98
Options exercisable at end of period (in dollars per share)	$ 87.72	$ 89.85	$ 90.32
Restricted Stock Awards
Options Outstanding
Weighted average fair value of options granted during the period	$ 10,650,077	$ 16,061,201	$ 1,141,675
Summary of restricted stock
Balance at beginning of year (in shares)	3,137,881	3,000,979	2,994,197
Granted (in shares)	98,800	143,053	9,550
Cancelled (in shares)	(34,650)	(6,151)	(2,768)
Balance at end of period (in shares)	3,202,031	3,137,881	3,000,979
Vested during the period (in shares)	83,822	87,081	75,043
Compensation expense recorded	$ 7,153,966	$ 7,540,747	$ 9,658,019