Asset-Backed Financing (Schedule Of Secured Notes With Related Maturity) (Details) (USD $) In Thousands, unless otherwise specified			12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 $675,306--0.59% [Member]	Dec. 31, 2012 $513,300--0.88% [Member]	Dec. 31, 2012 $573,300--0.76% [Member]	Dec. 31, 2012 $600,000--1.05% [Member]	Dec. 31, 2012 $562,499--1.55% [Member]	Dec. 31, 2012 $700,000--1.16% [Member]	Dec. 31, 2012 $700,000--2.11% [Member]	Dec. 31, 2012 $500,000--2.77% [Member]	Dec. 31, 2012 $486,000--3.94% [Member]	Dec. 31, 2012 $782,000--5.50% [Member]	Dec. 31, 2012 $950,000--5.20% [Member]
Debt Instrument [Line Items]
Issue Date			Jul. 31, 2012	Nov. 30, 2011	Aug. 31, 2011	Nov. 30, 2010	Dec. 31, 2009	Oct. 31, 2009	Jul. 31, 2009	May 31, 2009	Feb. 29, 2008	Aug. 31, 2007	May 31, 2007
Debt Instrument, Face Amount	$ 675,300	$ 1,090,000	$ 675,306	$ 513,300	$ 573,380	$ 600,000	$ 562,499	$ 700,000	$ 700,000	$ 500,000	$ 486,000	$ 782,000	$ 950,000
Principal Amount		$ 2,087,346
Weighted-Average Rate at Date of Issuance			0.59%	0.88%	0.76%	1.05%	1.55%	1.16%	2.11%	2.77%	3.94%	5.50%	5.20%
Maturity Date Beginning			Aug. 31, 2013	Nov. 30, 2012	Sep. 30, 2012	Dec. 31, 2011	Dec. 31, 2010	Oct. 31, 2010	Jul. 31, 2010	May 31, 2010	Feb. 28, 2009	Sep. 30, 2008	May 31, 2008
Maturity Date Ending			Jun. 30, 2018	Feb. 28, 2018	Aug. 30, 2017	Apr. 30, 2018	Jun. 30, 2017	Apr. 30, 2017	Feb. 28, 2017	Jan. 31, 2017	Dec. 31, 2013	May 31, 2015	Aug. 30, 2015