Credit Facilities Three Month Prior Year Credit Faciltiy Metrics (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Average Amount Outstanding in Canadian Dollars [Member]
Credit Facilities Summary [Line Items]
Canada Lease Warehouse Facility	$ 337,800,000	$ 18,100,000	$ 272,000,000	$ 6,100,000
Maximum Amount Outstanding in Canadian Dollars [Member]
Credit Facilities Summary [Line Items]
Canada Lease Warehouse Facility	368,500,000	75,600,000	368,500,000	75,600,000
Weighted Average Interest Rate [Member]
Credit Facilities Summary [Line Items]
Canada Lease Warehouse Facility	0.0269	0.0299	0.0272	0.0299
Syndicated warehouse facility	0.0122	0.0141	0.0144	0.0158
U.S. Lease Warehouse Facility				0.0160
Average Amount Outstanding [Member]
Credit Facilities Summary [Line Items]
Canada Lease Warehouse Facility	343,307,000	17,346,000	276,468,000	5,846,000
Syndicated warehouse facility	40,552,000	346,485,000	107,832,000	350,450,000
U.S. Lease Warehouse Facility				32,125,000
Maximum Amount Outstanding [Member]
Credit Facilities Summary [Line Items]
Canada Lease Warehouse Facility	374,496,000	72,539,000	374,496,000	72,539,000
Syndicated warehouse facility	138,250,000	817,845,000	429,839,000	826,859,000
U.S. Lease Warehouse Facility				$ 182,749,000