Share-Based Compensation - Share-based expense (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-based expense	$ 1.1	$ 1.2	$ 2.3	$ 2.4
Total recognized tax benefit	(0.3)	(0.3)	(0.6)	(0.7)
Share-based expense (net of tax)	0.8	0.9	1.7	1.7
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-based expense	0.0	0.1	0.0	0.3
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-based expense	$ 1.1	$ 1.1	$ 2.3	$ 2.1