Stock Based Compensation (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended	12 Months Ended	3 Months Ended
	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
Options Roll Forward
Shares outstanding under option, Beginning Balance	1,714,000
Weighted average exercise price, Beginning Balance	$ 16.11
Shares outstanding under option, Exercised	(251,000)
Shares outstanding under option, Exercised, Weighted average exercise price	$ 14.72
Shares outstanding under option, Ending Balance	1,463,000	1,714,000
Weighted average exercise price, Ending Balance	$ 16.35	$ 16.11
Weighted average remaining contractual term	1 year 6 months	1 year 8 months
Aggregate intrinsic value, outstanding	$ 64.6	$ 66.5
Status of nonvested restricted stock
Nonvested shares subject to restriction, Beginning Balance	1,266,000
Nonvested shares subject to restriction, weighted average exercise price	$ 43.57
Restricted shares granted to employees	563,000
Granted shares subject to restriction, weighted average exercise price	$ 57.90
Shares subject to restriction, Vested	(568,000)
Vested shares subject to restriction, weighted average exercise price	$ 38.35
Shares subject to restriction, Forfeited	(12,000)
Forfeited shares subject to restriction, weighted average exercise price	$ 45.10
Nonvested shares subject to restriction, Ending Balance	1,249,000	1,266,000
Nonvested shares subject to restriction, weighted average exercise price	$ 52.49	$ 43.57
Restricted Stock [Member]
Restricted stock compensation expense
Restricted stock compensation expense	$ 7.3		$ 4.5
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	563,074
2014 Stock Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares available for grant	7,200,000
Number of shares authorized	8,000,000
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