Financial Assets and Liabilities at Dates Indicated that Were Accounted for or Disclosed at Fair Value (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	$ 834,665	$ 951,301
Fair Value, Measurements, Recurring \| U.S. Government Agencies
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	134,639	200,252
Fair Value, Measurements, Recurring \| State and Municipal
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	175,109	173,111
Fair Value, Measurements, Recurring \| Mortgage-Backed
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	520,774	570,144
Fair Value, Measurements, Recurring \| Corporate Debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	1,992	1,978
Fair Value, Measurements, Recurring \| Trust Preferred
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	1,428	5,716
Fair Value, Measurements, Recurring \| Marketable Equity Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	723	100
Fair Value, Measurements, Recurring \| Interest Rate Swap Agreements
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other assets	1,413	1,529
Other liabilities	(1,413)	(1,529)
Fair Value, Measurements, Recurring \| Residential Mortgage Loans Held For Sale
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans held for sale	39,884	25,341
Fair Value, Inputs, Level 1 \| Fair Value, Measurements, Recurring \| Trust Preferred
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	0	3,249
Fair Value, Inputs, Level 2 \| Fair Value, Measurements, Recurring \| U.S. Government Agencies
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	134,639	200,252
Fair Value, Inputs, Level 2 \| Fair Value, Measurements, Recurring \| State and Municipal
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	175,109	173,111
Fair Value, Inputs, Level 2 \| Fair Value, Measurements, Recurring \| Mortgage-Backed
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	520,774	570,144
Fair Value, Inputs, Level 2 \| Fair Value, Measurements, Recurring \| Corporate Debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	1,992	1,978
Fair Value, Inputs, Level 2 \| Fair Value, Measurements, Recurring \| Marketable Equity Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	723	100
Fair Value, Inputs, Level 2 \| Fair Value, Measurements, Recurring \| Interest Rate Swap Agreements
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other assets	1,413	1,529
Other liabilities	(1,413)	(1,529)
Fair Value, Inputs, Level 2 \| Fair Value, Measurements, Recurring \| Residential Mortgage Loans Held For Sale
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans held for sale	39,884	25,341
Fair Value, Inputs, Level 3 \| Fair Value, Measurements, Recurring \| Trust Preferred
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	$ 1,428	$ 2,467

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

-Paragraph 16

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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

-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 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