Securities (Summary Of Cumulative Credit-Related OTTI Charges) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Mar. 31, 2012
Securities [Abstract]
Beginning balance of the amount related to credit loss for which a portion of OTTI was recognized in other comprehensive income	$ (18,332)	$ (18,398)
Additions related to credit loss for securities with previously recognized OTTI	(37)
Additions related to credit loss for securities with initial OTTI	(29)
Ending balance of the amount related to credit loss for which a portion of OTTI was recognized in other comprehensive income	$ (18,398)	$ (18,398)