Asset-Backed Financing (Schedule Of Secured Notes With Related Maturity) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011
$513,300--0.88% [Member]
Debt Instrument [Line Items]
Issue Date	November 2011
Principal Amount	$ 513,300
Weighted-Average Rate at Date of Issuance	0.88%
Maturity Date Beginning	November 2012
Maturity Date Ending	February 2018
$573,300--0.76% [Member]
Debt Instrument [Line Items]
Issue Date	August 2011
Principal Amount	573,380
Weighted-Average Rate at Date of Issuance	0.76%
Maturity Date Beginning	September 2012
Maturity Date Ending	August 2017
$600,000--1.05% [Member]
Debt Instrument [Line Items]
Issue Date	November 2010
Principal Amount	600,000
Weighted-Average Rate at Date of Issuance	1.05%
Maturity Date Beginning	December 2011
Maturity Date Ending	April 2018
$562,499--1.55% [Member]
Debt Instrument [Line Items]
Issue Date	December 2009
Principal Amount	562,499
Weighted-Average Rate at Date of Issuance	1.55%
Maturity Date Beginning	December 2010
Maturity Date Ending	June 2017
$700,000--1.16% [Member]
Debt Instrument [Line Items]
Issue Date	October 2009
Principal Amount	700,000
Weighted-Average Rate at Date of Issuance	1.16%
Maturity Date Beginning	October 2010
Maturity Date Ending	April 2017
$700,000--2.11% [Member]
Debt Instrument [Line Items]
Issue Date	July 2009
Principal Amount	700,000
Weighted-Average Rate at Date of Issuance	2.11%
Maturity Date Beginning	July 2010
Maturity Date Ending	February 2017
$500,000--2.77% [Member]
Debt Instrument [Line Items]
Issue Date	May 2009
Principal Amount	500,000
Weighted-Average Rate at Date of Issuance	2.77%
Maturity Date Beginning	May 2010
Maturity Date Ending	January 2017
$486,000--3.94% [Member]
Debt Instrument [Line Items]
Issue Date	February 2008
Principal Amount	486,000
Weighted-Average Rate at Date of Issuance	3.94%
Maturity Date Beginning	February 2009
Maturity Date Ending	December 2013
$782,000--5.50% [Member]
Debt Instrument [Line Items]
Issue Date	August 2007
Principal Amount	782,000
Weighted-Average Rate at Date of Issuance	5.50%
Maturity Date Beginning	September 2008
Maturity Date Ending	May 2015
$950,000--5.20% [Member]
Debt Instrument [Line Items]
Issue Date	May 2007
Principal Amount	$ 950,000
Weighted-Average Rate at Date of Issuance	5.20%
Maturity Date Beginning	May 2008
Maturity Date Ending	August 2015