Investment Securities (Roll Forward Of OTTI Recognized In Earnings) (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward]
Balance of credit related OTTI, beginning of year	$ 10,460	$ 26,320	$ 43,492
Reduction for payment of deferred interest	0	(16)	0
Reduction for securities sold	0	(15,844)	(22,943)
Additions for credit related OTTI not previously recognized	0	0	5,771
Balance of credit related OTTI, end of year	$ 10,460	$ 10,460	$ 26,320