Long-term Debt Tables (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013		Dec. 31, 2012
Debt Instrument [Line Items]
Long-term debt	$ 58.6		$ 84.7
Outstanding letters of credit	21.9		19.8
Amounts available to borrow	120.9	[1]	97.7	[1]
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Long-term debt	47.0		73.3
Obligations under Capital Leases [Member]
Debt Instrument [Line Items]
Long-term debt	$ 11.6		$ 11.4

[1] Excluding $100 million expansion feature.