Share-Based Compensation - Share-based expense (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-based expense	$ 1.2	$ 1.2
Total recognized tax benefit	(0.3)	(0.3)
Share-based expense (net of tax)	0.9	0.9
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-based expense	0	0.2
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-based expense	$ 1.2	$ 1.0