Share-based compensation Share-based compensation (Details 3) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Share-based compensation
Income tax benefit (in dollars)	$ 1.1	$ 0.5	$ 1.9	$ 1.3
Common stock
Share-based compensation
Shares granted			33,170	33,184
Fair value			0.8	0.8
Income tax benefit (in dollars)			$ 0.3	$ 0.3