Fair Value Measurements (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Fair value | Senior unsecured notes
Long-term Debt
Debt	$ 321.0	$ 309.8
Fair value | Other fixed rate debt
Long-term Debt
Debt	150.0	145.4
Fair value | Variable rate debt
Long-term Debt
Debt	283.9	298.1
Carrying value | Senior unsecured notes
Long-term Debt
Debt	298.5	298.3
Carrying value | Other fixed rate debt
Long-term Debt
Debt	151.4	140.7
Carrying value | Variable rate debt
Long-term Debt
Debt	$ 283.9	$ 298.1