Share-based Compensation (Details)	9 Months Ended	12 Months Ended
	Sep. 30, 2015 USD ($) $ / shares shares	Dec. 31, 2014 USD ($) $ / shares shares
Stock options
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]
Dividend yield (as a percent)	1.74%	1.60%
Expected life of option (in years)	3 years 6 months	3 years 7 months 6 days
Risk-free interest rate (as a percent)	1.17%	1.29%
Expected stock price volatility (as a percent)	34.59%	33.97%
Options Outstanding
Balance at beginning of year (in shares)	1,462,726	1,765,034
Granted (in shares)	40,500	102,050
Exercised (in shares)	(170,035)	(348,156)
Lapsed or cancelled (in shares)	(30,417)	(56,202)
Balance at end of period (in shares)	1,302,774	1,462,726
Options exercisable at end of period (in shares)	594,624	428,951
Weighted average fair value of options granted during the period | $	$ 1,112,152	$ 2,841,678
Weighted Average Exercise Price
Balance at beginning of year (in dollars per share) | $ / shares	$ 87.98	$ 83.24
Granted (in dollars per share) | $ / shares	117.50	119.12
Exercised (in dollars per share) | $ / shares	75.33	72.76
Lapsed or cancelled (in dollars per share) | $ / shares	98.41	90.03
Balance at end of period (in dollars per share) | $ / shares	90.30	87.98
Options exercisable at end of period (in dollars per share) | $ / shares	$ 88.44	$ 90.32
Restricted Stock Awards
Options Outstanding
Weighted average fair value of options granted during the period | $	$ 735,011	$ 1,141,675
Summary of restricted stock
Balance at beginning of year (in shares)	3,000,979	2,994,197
Granted (in shares)	6,053	9,550
Cancelled (in shares)	(3,717)	(2,768)
Balance at end of period (in shares)	3,003,315	3,000,979
Vested during the period (in shares)	87,081	75,043
Compensation expense recorded | $	$ 5,663,196	$ 9,658,019