Stock Based Compensation (Details) - USD ($)	3 Months Ended			6 Months Ended		12 Months Ended
	Jun. 30, 2015	Mar. 31, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Options Roll Forward
Shares outstanding under option, Beginning Balance	1,463,000	1,714,000		1,714,000
Weighted average exercise price, Beginning Balance	$ 16.35	$ 16.11		$ 16.11
Shares outstanding under option, Exercised	(103,000)	(251,000)
Shares outstanding under option, Exercised, Weighted average exercise price	$ 14.66	$ 14.72
Shares outstanding under option, Ending Balance	1,360,000	1,463,000		1,360,000		1,714,000
Weighted average exercise price, Ending Balance	$ 16.48	$ 16.35		$ 16.48		$ 16.11
Weighted average remaining contractual term	1 year 4 months	1 year 6 months				1 year 8 months
Aggregate intrinsic value, outstanding	$ 54,900,000	$ 64,600,000		$ 54,900,000		$ 66,500,000
Status of nonvested restricted stock
Nonvested shares subject to restriction, Beginning Balance	1,249,000	1,266,000		1,266,000
Nonvested shares subject to restriction, weighted average exercise price	$ 52.49	$ 43.57		$ 43.57
Restricted shares granted to employees	124,000	563,000
Granted shares subject to restriction, weighted average exercise price	$ 60.97	$ 57.90
Shares subject to restriction, Vested	(20,000)	(568,000)
Vested shares subject to restriction, weighted average exercise price	$ 61.79	$ 38.35
Shares subject to restriction, Forfeited	(5,000)	(12,000)
Forfeited shares subject to restriction, weighted average exercise price	$ 52.82	$ 45.10
Nonvested shares subject to restriction, Ending Balance	1,348,000	1,249,000		1,348,000		1,266,000
Nonvested shares subject to restriction, weighted average exercise price	$ 53.15	$ 52.49		$ 53.15		$ 43.57
Restricted Stock [Member]
Restricted stock compensation expense
Restricted stock compensation expense	$ 6,900,000		$ 5,400,000	$ 14,200,000	$ 9,900,000
Stock Incentive Plan 2004 [Member] | Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period				3 years
Term of award				10 years
Stock Incentive Plan 2004 [Member] | Restricted Stock [Member]
Status of nonvested restricted stock
Restricted shares granted to employees				669,754
2014 Stock Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares available for grant	7,000,000			7,000,000
Number of shares authorized	8,000,000			8,000,000
2014 Stock Incentive Plan [Member] | Restricted Stock [Member]
Status of nonvested restricted stock
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Share-based Liabilities Paid				$ 16,983
First Half Vested | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period				2 years
Percent of awards vested				50.00%
Second Half Vested | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period				3 years