Impairment of Investment Securities - Schedule of Unrealized Losses and Estimated Fair Values (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012		Dec. 31, 2011
Schedule of Trading Securities and Other Trading Assets [Line Items]
Estimated Fair Value, Less Than 12 Months			$ 61,767
Gross Unrealized Losses Less Than 12 Months			(701)
Estimated Fair Value, 12 Months or More			22,943
Gross Unrealized Losses 12 Months or More			(31,785)
Total Estimated Fair Value			84,710
Total Gross Unrealized Losses			(32,486)
Pooled Trust Preferred Collateralized Debt Obligations [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Estimated Fair Value, Less Than 12 Months			0
Gross Unrealized Losses Less Than 12 Months			0
Estimated Fair Value, 12 Months or More			22,927
Gross Unrealized Losses 12 Months or More			(31,785)
Total Estimated Fair Value			22,927
Total Gross Unrealized Losses			(31,785)
Debt Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Estimated Fair Value, Less Than 12 Months	2,424
Gross Unrealized Losses Less Than 12 Months	(2)
Estimated Fair Value, 12 Months or More	23,010
Gross Unrealized Losses 12 Months or More	(29,647)
Total Estimated Fair Value	25,434
Total Gross Unrealized Losses	(29,649)
Equities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Estimated Fair Value, Less Than 12 Months	0
Gross Unrealized Losses Less Than 12 Months	0
Estimated Fair Value, 12 Months or More	0
Gross Unrealized Losses 12 Months or More	0
Total Estimated Fair Value	0
Total Gross Unrealized Losses	0
Corporate Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Estimated Fair Value, Less Than 12 Months			4,536
Gross Unrealized Losses Less Than 12 Months			(562)
Estimated Fair Value, 12 Months or More			0
Gross Unrealized Losses 12 Months or More			0
Total Estimated Fair Value			4,536
Total Gross Unrealized Losses			(562)
Obligations of U.S. Government Agencies [Member] | Mortgage Backed Securities - Residential [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Estimated Fair Value, Less Than 12 Months	0		1,086
Gross Unrealized Losses Less Than 12 Months	0		(6)
Estimated Fair Value, 12 Months or More	14		16
Gross Unrealized Losses 12 Months or More	0	[1]	0	[1]
Total Estimated Fair Value	14		1,102
Total Gross Unrealized Losses	0		(6)
Obligations of U.S. Government-Sponsored Enterprises [Member] | Mortgage Backed Securities - Residential [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Estimated Fair Value, Less Than 12 Months	26		25
Gross Unrealized Losses Less Than 12 Months	0	[1]	0	[1]
Estimated Fair Value, 12 Months or More	0		0
Gross Unrealized Losses 12 Months or More	0		0
Total Estimated Fair Value	26		25
Total Gross Unrealized Losses	0		0
Obligations of U.S. Government-Sponsored Enterprises [Member] | Other Government Sponsored Enterprises [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Estimated Fair Value, Less Than 12 Months	2,398		55,969
Gross Unrealized Losses Less Than 12 Months	(2)		(132)
Estimated Fair Value, 12 Months or More	0		0
Gross Unrealized Losses 12 Months or More	0		0
Total Estimated Fair Value	2,398		55,969
Total Gross Unrealized Losses	(2)		(132)
Obligations of U.S. Government-Sponsored Enterprises [Member] | Pooled Trust Preferred Collateralized Debt Obligations [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Estimated Fair Value, Less Than 12 Months	0
Gross Unrealized Losses Less Than 12 Months	0
Estimated Fair Value, 12 Months or More	22,996
Gross Unrealized Losses 12 Months or More	(29,647)
Total Estimated Fair Value	22,996
Total Gross Unrealized Losses	(29,647)
Obligations of U.S. Government-Sponsored Enterprises [Member] | Mortgage Backed Securities - Commercial [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Estimated Fair Value, Less Than 12 Months			151
Gross Unrealized Losses Less Than 12 Months			(1)
Estimated Fair Value, 12 Months or More			0
Gross Unrealized Losses 12 Months or More			0
Total Estimated Fair Value			151
Total Gross Unrealized Losses			$ (1)

[1] Gross unrealized losses related to these types of securities are less than $1 thousand.