Debt (Details 2) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	May 31, 2011
Revolving Loans
Revolving loans
Total Amount Committed by Lenders	$ 464.4
Outstanding Borrowings	112.5
Outstanding Letters of Credit	171.2
Total Amount Available	180.7
Amended Credit Agreement
Revolving loans
Weighted Average Interest Rate (as a percent)	1.30%
Total Amount Committed by Lenders	250.0	250.0
Outstanding Borrowings	112.5
Outstanding Letters of Credit	0.6
Total Amount Available	136.9
Other revolving loans
Revolving loans
Total Amount Committed by Lenders	214.4
Outstanding Letters of Credit	170.6
Total Amount Available	$ 43.8