Fair Value of Financial Instruments (Detail) - Assets Recorded at Fair Value on a Recurring Basis (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012
Securities available for sale	$ 314,597	$ 253,798	$ 442,531
Residential mortgage servicing rights	15,297	13,910
Derivative financial instruments	2,140	2,561
Total assets at fair value	332,034	270,269
US Treasury and Government [Member] \| Fair Value, Inputs, Level 1 [Member]
Securities available for sale	1,019	0
US Treasury and Government [Member] \| Fair Value, Inputs, Level 2 [Member]
Securities available for sale	225	1,278
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	1,244	1,278
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	13,263	13,483
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	13,263	13,483
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	3,504	3,332
Collateralized Debt Obligations [Member]
Securities available for sale	3,504	3,332
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	145,308	74,304
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	145,308	74,304
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	144,507	154,883
Collateralized Mortgage Obligations [Member] \| Fair Value, Inputs, Level 3 [Member]
Securities available for sale	0	0
Collateralized Mortgage Obligations [Member]
Securities available for sale	144,507	154,883
Other Equity And Debt Securities [Member] \| Fair Value, Inputs, Level 1 [Member]
Securities available for sale	2,147	1,929
Other Equity And Debt Securities [Member] \| Fair Value, Inputs, Level 2 [Member]
Securities available for sale	2,987	2,999
Other Equity And Debt Securities [Member] \| Fair Value, Inputs, Level 3 [Member]
Securities available for sale	1,637	1,590
Other Equity And Debt Securities [Member]
Securities available for sale	6,771	6,518
Fair Value, Inputs, Level 1 [Member]
Securities available for sale	3,166	1,929
Residential mortgage servicing rights	0	0
Derivative financial instruments	2,140	2,561
Total assets at fair value	5,306	4,490
Fair Value, Inputs, Level 2 [Member]
Securities available for sale	306,290	246,947
Residential mortgage servicing rights	0	0
Derivative financial instruments	0	0
Total assets at fair value	306,290	246,947
Fair Value, Inputs, Level 3 [Member]
Securities available for sale	5,141	4,922
Residential mortgage servicing rights	15,297	13,910
Derivative financial instruments	0	0
Total assets at fair value	$ 20,438	$ 18,832

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name FASB Staff Position (FSP)

-Number FAS115-1/124-1

-Paragraph 15D

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Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 12

-Subparagraph b

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6871852&loc=d3e26610-111562

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

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Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name FASB Staff Position (FSP)

-Number FAS115-1/124-1

-Paragraph 15C

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Reference 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 25

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=7534914&loc=d3e22054-111558

Reference 7: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name FASB Staff Position (FSP)

-Number FAS115-1/124-1

-Paragraph 15E

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Reference 8: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 13

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Reference 9: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 14

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 10: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 133

-Paragraph 22

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+ Details