Fair Values of Assets and Liabilities - Schedule of Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012		Dec. 31, 2011
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Debt Securities	$ 1,128,962		$ 1,140,916
Fair Value of Investment Securities	1,130,822		1,142,776
Other investments	32,479		39,796
Loans Held for Sale			13,412
Other Assets	18,122	[1]	16,064	[1]
Total Assets	1,181,423		1,212,048
Other Liabilities	20,004	[1]	18,986	[1]
Total Liabilities	20,004		18,986
Equities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value of Investment Securities	1,860		1,860
US Government Agencies Debt Securities [Member] | Mortgage Backed Securities Residential [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Debt Securities	33,355		36,194
Obligations of U.S. Government-Sponsored Enterprises [Member] | Mortgage Backed Securities Residential [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Debt Securities	818,278		801,031
Obligations of U.S. Government-Sponsored Enterprises [Member] | Mortgage Backed Securities Commercial [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Debt Securities	166		193
Obligations of U.S. Government-Sponsored Enterprises [Member] | Other Government Sponsored Enterprises [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Debt Securities	242,881		268,648
Obligations of States and Political Subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Debt Securities	87		459
Corporate securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Debt Securities	11,144		11,411
Pooled Trust Preferred Collateralized Debt Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Debt Securities	23,051		22,980
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Debt Securities	0		0
Fair Value of Investment Securities	440		440
Other investments	0		0
Loans Held for Sale			0
Other Assets	0	[1]	0	[1]
Total Assets	440		440
Other Liabilities	0	[1]	0	[1]
Total Liabilities	0		0
Level 1 [Member] | Equities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value of Investment Securities	440		440
Level 1 [Member] | US Government Agencies Debt Securities [Member] | Mortgage Backed Securities Residential [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Debt Securities	0		0
Level 1 [Member] | Obligations of U.S. Government-Sponsored Enterprises [Member] | Mortgage Backed Securities Residential [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Debt Securities	0		0
Level 1 [Member] | Obligations of U.S. Government-Sponsored Enterprises [Member] | Mortgage Backed Securities Commercial [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Debt Securities	0		0
Level 1 [Member] | Obligations of U.S. Government-Sponsored Enterprises [Member] | Other Government Sponsored Enterprises [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Debt Securities	0		0
Level 1 [Member] | Obligations of States and Political Subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Debt Securities	0		0
Level 1 [Member] | Corporate securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Debt Securities	0		0
Level 1 [Member] | Pooled Trust Preferred Collateralized Debt Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Debt Securities	0		0
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Debt Securities	1,105,911		1,117,936
Fair Value of Investment Securities	1,105,911		1,117,936
Other investments	32,479		39,796
Loans Held for Sale			0
Other Assets	18,122	[1]	16,064	[1]
Total Assets	1,156,512		1,173,796
Other Liabilities	20,004	[1]	18,986	[1]
Total Liabilities	20,004		18,986
Level 2 [Member] | Equities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value of Investment Securities	0		0
Level 2 [Member] | US Government Agencies Debt Securities [Member] | Mortgage Backed Securities Residential [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Debt Securities	33,355		36,194
Level 2 [Member] | Obligations of U.S. Government-Sponsored Enterprises [Member] | Mortgage Backed Securities Residential [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Debt Securities	818,278		801,031
Level 2 [Member] | Obligations of U.S. Government-Sponsored Enterprises [Member] | Mortgage Backed Securities Commercial [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Debt Securities	166		193
Level 2 [Member] | Obligations of U.S. Government-Sponsored Enterprises [Member] | Other Government Sponsored Enterprises [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Debt Securities	242,881		268,648
Level 2 [Member] | Obligations of States and Political Subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Debt Securities	87		459
Level 2 [Member] | Corporate securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Debt Securities	11,144		11,411
Level 2 [Member] | Pooled Trust Preferred Collateralized Debt Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Debt Securities	0		0
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Debt Securities	23,051		22,980
Fair Value of Investment Securities	24,471		24,400
Other investments	0		0
Loans Held for Sale			13,412
Other Assets	0	[1]	0	[1]
Total Assets	24,471		37,812
Other Liabilities	0	[1]	0	[1]
Total Liabilities	0		0
Level 3 [Member] | Equities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value of Investment Securities	1,420		1,420
Level 3 [Member] | US Government Agencies Debt Securities [Member] | Mortgage Backed Securities Residential [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Debt Securities	0		0
Level 3 [Member] | Obligations of U.S. Government-Sponsored Enterprises [Member] | Mortgage Backed Securities Residential [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Debt Securities	0		0
Level 3 [Member] | Obligations of U.S. Government-Sponsored Enterprises [Member] | Mortgage Backed Securities Commercial [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Debt Securities	0		0
Level 3 [Member] | Obligations of U.S. Government-Sponsored Enterprises [Member] | Other Government Sponsored Enterprises [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Debt Securities	0		0
Level 3 [Member] | Obligations of States and Political Subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Debt Securities	0		0
Level 3 [Member] | Corporate securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Debt Securities	0		0
Level 3 [Member] | Pooled Trust Preferred Collateralized Debt Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Debt Securities	$ 23,051		$ 22,980

[1] Non-hedging interest rate derivatives