Share-Based Awards - Summary of Compensation Costs (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total share-based expense	$ 4.2	$ 5.4	$ 4.8
Total recognized tax benefit	(1.3)	(1.8)	(1.2)
Share-based expense (net of tax)	2.9	3.6	3.6
Cash received upon option exercise	7.6	20.9	6.1
Intrinsic value of options exercised	6.7	13.4	3.5
Tax benefit realized upon option exercise	2.5	2.3	1.3
Fair value of stock vested	5.2	4.2	5.5
Stock Options
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total share-based expense	0.7	1.1	1.2
Incremental non cash share based compensation expense
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total share-based expense	0.5	1.2	0
Restricted Stock Units (RSUs)
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total share-based expense	$ 3.0	$ 3.1	$ 3.6