Accounts Receivable (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Trade accounts receivable
Gross accounts receivable	$ 288.4	$ 238.0
Allowance for doubtful accounts	(5.6)	(5.1)
Accounts receivable, net	282.8	232.9
Allowance for doubtful accounts
Summary of activity in the entity's allowance for doubtful accounts
Balance at Beginning of Period	5.1	5.4	5.4
Additions Charged to Expense	0.9	0.3	1.2
Deductions Amounts Written Off	(0.4)	(0.6)	(1.2)
Balance at End of Period	$ 5.6	$ 5.1	$ 5.4