Subsequent Events (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended			60 Months Ended			1 Months Ended
	Mar. 31, 2013		Mar. 31, 2012	Apr. 30, 2018	Dec. 31, 2012		Apr. 30, 2013 Investments in affiliates [Member]	Apr. 30, 2013 Subsequent Event [Member] Vessel	Apr. 30, 2013 Line of Credit US [Member]
Subsequent Event [Line Items]
Investments in affiliates	$ 0		$ 1.5				$ 90.0
Number of vessels received								5
Guarantor obligations, maximum exposure, undiscounted	96.7	[1]			104.5	[1]
Unsecured revolving credit facility									$ 575
Debt Instrument, Maturity Date Range, End				Apr. 30, 2013

[1] The carrying values of liabilities on the balance sheet for our commercial commitments were $6.2 million at March 31, 2013 and $6.4 million at December 31, 2012. The expiration dates for our commitments range from 2013–2022. We are not aware of any event that would require us to satisfy any of our commitments.