Stock Based Compensation (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended	12 Months Ended	3 Months Ended			3 Months Ended
	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2014 Restricted Stock [Member]	Mar. 31, 2013 Restricted Stock [Member]	Mar. 31, 2014 2004 Plan [Member]	Mar. 31, 2014 2004 Plan [Member] Stock Option [Member]	Mar. 31, 2014 First Half Vested 2004 Plan [Member] Restricted Stock [Member]	Mar. 31, 2014 Second Half Vested 2004 Plan [Member] Restricted Stock [Member]	Mar. 31, 2013 Retiring named executive officers [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period						3 years	2 years	3 years
Term of award						10 years
Percent of awards vested							50.00%
Number of shares authorized for grant					25,000,000
Shares available for future issuance					2,600,000
Options Roll Forward
Shares outstanding under option, Beginning Balance	1,997,000
Weighted average exercise price, Beginning Balance	$ 15.82
Shares outstanding under option, Exercised	(54,000)
Shares outstanding under option, Exercised, Weighted average exercise price	$ 14.41
Shares outstanding under option, Ending Balance	1,943,000	1,997,000
Weighted average exercise price, Ending Balance	$ 15.86	$ 15.82
Weighted average remaining contractual term	2 years 5 months	2 years 7 months
Aggregate intrinsic value, outstanding	$ 88.6	$ 80.0
Restricted stock compensation expense
Restricted stock compensation expense			$ 4.5	$ 11.1					$ 5.5
Status of nonvested restricted stock
Nonvested shares subject to restriction, Beginning Balance	1,411,000
Nonvested shares subject to restriction, weighted average exercise price	$ 37.86
Restricted shares granted to employees	420,000		419,926
Granted shares subject to restriction, weighted average exercise price	$ 53.90
Shares subject to restriction, Vested	(498,000)
Vested shares subject to restriction, weighted average exercise price	$ 37.38
Shares subject to restriction, Forfeited	(16,000)
Forfeited shares subject to restriction, weighted average exercise price	$ 39.54
Nonvested shares subject to restriction, Ending Balance	1,317,000	1,411,000
Nonvested shares subject to restriction, weighted average exercise price	$ 43.08	$ 37.86