Credit Facilities Prior Year to Date Credit Faciltiy Metrics (Details) (USD $)			3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2013 Average Amount Outstanding in Canadian Dollars [Member]	Mar. 31, 2012 Average Amount Outstanding in Canadian Dollars [Member]	Mar. 31, 2013 Weighted Average Interest Rate [Member]	Mar. 31, 2012 Weighted Average Interest Rate [Member]	Mar. 31, 2013 Average Amount Outstanding [Member]	Mar. 31, 2012 Average Amount Outstanding [Member]	Mar. 31, 2013 Maximum Amount Outstanding [Member]	Mar. 31, 2012 Maximum Amount Outstanding [Member]	Mar. 31, 2013 Maximum Amount Outstanding in Canadian Dollars [Member]	Mar. 31, 2012 Maximum Amount Outstanding in Canadian Dollars [Member]
Credit Facilities Summary [Line Items]
Canada Lease Warehouse Facility			$ 387,600,000	$ 212,400,000	$ 0.0267	$ 0.0259	$ 381,546,000	$ 212,485,000	$ 407,141,000	$ 248,176,000	$ 413,600,000	$ 248,000,000
Unamortized Debt Issuance Expense	9,800,000	4,500,000
Syndicated warehouse facility					0.0140	0.0163	52,682,000	128,309,000	948,272,000	621,257,000
U.S. Lease Warehouse Facility					$ 0.0182		$ 57,581,000		$ 863,721,000