Fair Value Measurement (Schedule Of Assumptions Used To Determine Fair Value) (Details)	6 Months Ended	12 Months Ended
	Jun. 30, 2012	Dec. 31, 2011
Minimum [Member]
Fair Value Measurement [Line Items]
Cumulative probability of earning maximum rate until maturity	0.00%	0.00%
Cumulative probability of principle returned prior to maturity	95.80%	95.40%
Cumulative probability of default at some future point	1.40%	1.30%
Liquidity risk premium	4.00%	4.50%
Maximum [Member]
Fair Value Measurement [Line Items]
Cumulative probability of earning maximum rate until maturity	0.20%	0.10%
Cumulative probability of principle returned prior to maturity	98.60%	98.70%
Cumulative probability of default at some future point	4.20%	4.60%
Liquidity risk premium	4.50%	5.00%