Long-term Debt - Tables (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014		Dec. 31, 2013
Debt Instrument [Line Items]
Long-term debt	$ 18.0		$ 57.6
Outstanding letters of credit	18.9		21.8
Amounts available to borrow	165.4	[1]	122.7	[1]
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Long-term debt	5.0		46.3
Obligations under capital leases [Member]
Debt Instrument [Line Items]
Long-term debt	$ 13.0		$ 11.3

[1] Excluding $100 million expansion feature