Fair Value of Financial Instruments (Detail) - Financial instruments measured at fair value on a recurring basis (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012		Dec. 31, 2011		Sep. 30, 2011
Securities available for sale	$ 236,048		$ 404,550		$ 412,108
Residential mortgage servicing rights	12,504	[1]	10,663	[1]
Derivative financial instruments	2,887	[1]	2,238	[1]
Total assets at fair value	251,439		417,451
US Treasury and Government [Member] | Fair Value, Inputs, Level 1 [Member]
Securities available for sale	0		0
US Treasury and Government [Member] | Fair Value, Inputs, Level 2 [Member]
Securities available for sale	1,362		1,823
US Treasury and Government [Member] | Fair Value, Inputs, Level 3 [Member]
Securities available for sale	0		0
US Treasury and Government [Member]
Securities available for sale	1,362		1,823
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Securities available for sale	0		0
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Securities available for sale	6,572		488
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Securities available for sale	0		0
US States and Political Subdivisions Debt Securities [Member]
Securities available for sale	6,572		488
Collateralized Debt Obligations [Member] | Fair Value, Inputs, Level 1 [Member]
Securities available for sale	0		0
Collateralized Debt Obligations [Member] | Fair Value, Inputs, Level 2 [Member]
Securities available for sale	0		0
Collateralized Debt Obligations [Member] | Fair Value, Inputs, Level 3 [Member]
Securities available for sale	3,112		3,247
Collateralized Debt Obligations [Member]
Securities available for sale	3,112		3,247
Collateralized Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Securities available for sale	0		0
Collateralized Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Securities available for sale	51,363		84,399
Collateralized Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Securities available for sale	0		0
Collateralized Mortgage Backed Securities [Member]
Securities available for sale	51,363		84,399
Collateralized Mortgage Obligations [Member] | Fair Value, Inputs, Level 1 [Member]
Securities available for sale	0		0
Collateralized Mortgage Obligations [Member] | Fair Value, Inputs, Level 2 [Member]
Securities available for sale	167,241		256,615
Collateralized Mortgage Obligations [Member] | Fair Value, Inputs, Level 3 [Member]
Securities available for sale	0		52,680
Collateralized Mortgage Obligations [Member]
Securities available for sale	167,241		309,295
Other Equity And Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Securities available for sale	1,941		1,000
Other Equity And Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Securities available for sale	2,928		3,197
Other Equity And Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Securities available for sale	1,529		1,101
Other Equity And Debt Securities [Member]
Securities available for sale	6,398		5,298
Fair Value, Inputs, Level 1 [Member]
Securities available for sale	1,941		1,000
Residential mortgage servicing rights	0		0
Derivative financial instruments	2,887		2,238
Total assets at fair value	4,828		3,238
Fair Value, Inputs, Level 2 [Member]
Securities available for sale	229,466		346,522
Residential mortgage servicing rights	0		0
Derivative financial instruments	0		0
Total assets at fair value	229,466		346,522
Fair Value, Inputs, Level 3 [Member]
Securities available for sale	4,641		57,028
Residential mortgage servicing rights	12,504		10,663
Derivative financial instruments	0		0
Total assets at fair value	$ 17,145		$ 67,691

[1] Included as part of Other Assets in the Consolidated Balance Sheets.