Fair Value Disclosures (Assets Measured at Fair Value on Recurring Basis Using Significant Unobservable Inputs) (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011		Sep. 30, 2012		Sep. 30, 2011
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at January 1, 2011	$ 15,909		$ 17,532		$ 16,723		$ 15,884
Other-than-temporary impairment (1)	0	[1]	0	[1]	2,948	[1]	0	[1]
Included in other comprehensive income (before taxes)	(270)		(1,362)		(5,387)		286
Sales	0		0		(18,782)		0
Transfers into Level III	0		0		20,137		0
Transfers out of Level III	0		0		0		0
Balance at September 30, 2011	15,639		16,170		15,639		16,170
Equity Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at January 1, 2011	3,159		3,399		3,430		3,381
Other-than-temporary impairment (1)	0	[1]	0	[1]	(144)	[1]	0	[1]
Included in other comprehensive income (before taxes)	1		31		(126)		49
Sales	0		0		0		0
Transfers into Level III	0		0		0		0
Transfers out of Level III	0		0		0		0
Balance at September 30, 2011	3,160		3,430		3,160		3,430
Other Structured Financial Products [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at January 1, 2011	8,462		14,133		13,293		12,503
Other-than-temporary impairment (1)	0	[1]	0	[1]	0	[1]	0	[1]
Included in other comprehensive income (before taxes)	(70)		(1,393)		(4,901)		237
Sales	0		0		0		0
Transfers into Level III	0		0		0		0
Transfers out of Level III	0		0		0		0
Balance at September 30, 2011	8,392		12,740		8,392		12,740
Non Agency Mortgage Backed Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at January 1, 2011	4,288		0		0		0
Other-than-temporary impairment (1)	0	[1]	0	[1]	3,092	[1]	0	[1]
Included in other comprehensive income (before taxes)	(201)		0		(360)		0
Sales	0		0		(18,782)		0
Transfers into Level III	0		0		20,137		0
Transfers out of Level III	0		0		0		0
Balance at September 30, 2011	$ 4,087		$ 0		$ 4,087		$ 0

[1] Included in noninterest income, net impairment losses recognized in earnings.