Credit Facilities Three Month Current Year Credit Facility Metrics (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Maximum Amount Outstanding in Canadian Dollars [Member]
Credit Facilities Summary [Line Items]
Canada Lease Warehouse Facility	$ 368,500,000	$ 184,600,000
Weighted Average Interest Rate [Member]
Credit Facilities Summary [Line Items]
Syndicated warehouse facility	0.0144	0.0156
Canada Lease Warehouse Facility	0.0270	0.0269
Average Amount Outstanding in Canadian Dollars [Member]
Credit Facilities Summary [Line Items]
Canada Lease Warehouse Facility	$ 296,900,000	$ 41,600,000