Stock Based Compensation (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended			6 Months Ended		12 Months Ended
	Jun. 30, 2016	Mar. 31, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Options Roll Forward
Shares outstanding under option, Beginning Balance	1,102,000	1,267,000		1,267,000
Weighted average exercise price, Beginning Balance	$ 16.56	$ 16.59		$ 16.59
Shares outstanding under option, Exercised	(224,000)	(165,000)
Shares outstanding under option, Exercised, Weighted average exercise price	$ 14.67	$ 16.81
Shares outstanding under option, Ending Balance	878,000	1,102,000		878,000		1,267,000
Weighted average exercise price, Ending Balance	$ 17.04	$ 16.56		$ 17.04		$ 16.59
Weighted average remaining contractual term	6 months	8 months				11 months
Aggregate intrinsic value, outstanding	$ 10.9	$ 24.1		$ 10.9		$ 33.7
Status of nonvested restricted stock
Nonvested shares subject to restriction, Beginning Balance	1,482,000	1,326,000		1,326,000
Nonvested shares subject to restriction, weighted average exercise price	$ 45.03	$ 53.18		$ 53.18
Restricted shares granted to employees	25,000	668,000
Granted shares subject to restriction, weighted average exercise price	$ 38.62	$ 29.61
Shares subject to restriction, Vested	(55,000)	(493,000)
Vested shares subject to restriction, weighted average exercise price	$ 60.23	$ 46.06
Shares subject to restriction, Forfeited	(12,000)	(19,000)
Forfeited shares subject to restriction, weighted average exercise price	$ 47.22	$ 42.84
Nonvested shares subject to restriction, Ending Balance	1,440,000	1,482,000		1,440,000		1,326,000
Nonvested shares subject to restriction, weighted average exercise price	$ 44.32	$ 45.03		$ 44.32		$ 53.18
Restricted Stock [Member]
Restricted stock compensation expense
Restricted stock compensation expense	$ 6.7		$ 6.9	$ 13.1	$ 14.2
Status of nonvested restricted stock
Restricted shares granted to employees				667,874
Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Share-based Awards Other than Options	38.2			$ 38.2
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition				2 years
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance share compensation expense	$ 4.2		$ 2.9	$ 7.2	$ 6.5
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
2014 Stock Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares available for grant	5,700,000			5,700,000
Number of shares authorized	8,000,000			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
Director [Member] | Restricted Stock [Member]
Status of nonvested restricted stock
Restricted shares granted to employees				25,048