Employee Retirement Plans (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Components of net retirement cost
Service cost	$ 0.2	$ 0.3
Interest	4.8	4.9
Expected return on plan assets	(5.6)	(5.7)
Actuarial loss	0.9	0.5
Defined benefit expense	0.3	0
Profit sharing	2.6	2.3
Net expense	$ 2.9	$ 2.3