Credit Facilities Three Month Current Year Credit Facility Metrics (Details) (USD $)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
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]
Syndicated warehouse facility	0.0140	0.0163
Canada Lease Warehouse Facility	0.0267	0.0259
Average Amount Outstanding in Canadian Dollars [Member]
Credit Facilities Summary [Line Items]
Canada Lease Warehouse Facility	$ 387,600,000	$ 212,400,000