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