Share-based Compensation (Details) (USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Restricted Stock Awards
Options Outstanding
Weighted average fair value of options granted during the period	$ 0		$ 17,386,949
Summary of restricted stock
Balance at beginning of year (in shares)	2,994,197	2,804,901	2,804,901
Granted (in shares)	0		192,563
Cancelled (in shares)	(1,000)		(3,267)
Balance at end of period (in shares)	2,993,197		2,994,197
Vested during the period (in shares)	67,418		21,074
Compensation expense recorded	2,340,667		6,713,155
Weighted average fair value of restricted stock granted during the period	0		17,386,949
Stock options
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]
Dividend yield (as a percent)	1.80%		1.92%
Expected life of option	3 years 8 months 12 days		4 years 1 month 6 days
Risk-free interest rate (as a percent)	0.94%		0.96%
Expected stock price volatility (as a percent)	35.00%		36.12%
Options Outstanding
Balance at beginning of year (in shares)	1,765,034	1,201,000	1,201,000
Granted (in shares)	3,000		828,100
Exercised (in shares)	(154,531)		(223,531)
Lapsed or cancelled (in shares)	(8,667)		(40,535)
Balance at end of period (in shares)	1,604,836		1,765,034
Options exercisable at end of period (in shares)	581,744		461,458
Weighted average fair value of options granted during the period	69,805		18,041,576
Weighted Average Exercise Price
Balance at beginning of year (in dollars per share)	$ 83.24	$ 75.05	$ 75.05
Granted (in dollars per share)	$ 98.58		$ 87.23
Exercised (in dollars per share)	$ 66.52		$ 53.93
Lapsed or cancelled (in dollars per share)	$ 80.49		$ 83.94
Balance at end of period (in dollars per share)	$ 84.89		$ 83.24
Options exercisable at end of period (in dollars per share)	$ 86.66		$ 89.38
Summary of restricted stock
Compensation expense recorded	2,100,000	1,300,000
Weighted average fair value of restricted stock granted during the period	$ 69,805		$ 18,041,576