Stock-Based Compensation (Details 2) (General and Administrative Expense, USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Restricted Stock Unit Awards
Compensation Expense Recognized Included in General and Administrative Expenses
Compensation expense	$ 4.9	$ 7.1	$ 5.7
Related income tax benefit	1.9	1.5	2.5
Stock Options
Compensation Expense Recognized Included in General and Administrative Expenses
Compensation expense	1.7	2.4	3.1
Related income tax benefit	$ 0.7	$ 1.0	$ 1.3