Share-Based Compensation (Details 2) (Stock options, USD $)	6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013
Stock options
Summary of option activity and related information
Number of Options Outstanding, beginning of the period (in shares)	4,075,000
Number of options granted (in shares)	452,000
Number of options exercised (in shares)	(289,000)
Number of options forfeited or expired (in shares)	(30,000)
Number of Options Outstanding, end of the period (in shares)	4,208,000
Weighted Average Exercise Price of Options Outstanding, beginning of the period (in dollars per share)	$ 55.50
Weighted Average Exercise Price of Options Granted (in dollars per share)	$ 73.64
Weighted Average Exercise Price of Options Exercised (in dollars per share)	$ 56.61
Weighted Average Exercise Price of Options Forfeited or expired (in dollars per share)	$ 58.36
Weighted Average Exercise Price of Options Outstanding, end of the period (in dollars per share)	$ 57.35
Outstanding Aggregate Intrinsic Value of in-the-money Options	$ 77,718,000
Weighted Average Remaining Contractual Term Outstanding	5 years 8 months 26 days
Number of Options Exercisable (in shares)	2,870,000
Weighted Average Exercise Price of options exercisable (in dollars per share)	$ 56.05
Aggregate Intrinsic Value of in-the-money Options Exercisable	56,782,000
Weighted Average Remaining Contractual Term Exercisable	4 years 5 months 5 days
Share-based Compensation Arrangement by Share-based Payment Award, Options Unvested and related information
Unvested at the beginning of the period (in shares)	1,425,000
Granted (in shares)	452,000
Vested (in shares)	(518,620)	(646,736)
Forfeited (in shares)	(19,000)
Unvested at the end of the period (in shares)	1,339,000
Unvested at the beginning of the period (in dollars per share)	$ 13.64
Granted (in dollars per share)	$ 17.93	$ 12.57
Vested (in dollars per share)	$ 14.57
Forfeited (in dollars per share)	$ 12.78
Unvested at the end of the period (in dollars per share)	$ 14.75
Total fair value of options vested	7,600,000	7,800,000
Unrecognized compensation cost related to unvested stock options granted	$ 15,200,000
Period of recognition for unrecognized compensation cost related to unvested stock options granted	2 years 8 months 12 days