Fair Value Measurement of Assets and Liabilities - Assets and Liabilities Measured at Fair Value on Recurring and Non-Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	$ 958,656	$ 807,816
Trading securities	14,170	22,157
U.S. Treasury securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	89,786	97,625
U.S. government agency securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	55,808	45,762
Obligations of states and political subdivisions [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	39,234	16,627
Residential mortgage-backed securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	573,827	510,154
Trust preferred securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	68,413	57,432
Corporate and other debt securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	84,246	30,708
Equity securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	47,342	49,508
Fair Value [Member] | Recurring fair value measurements [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	958,656	807,816
Trading securities	14,170	22,157
Loans held for sale	48,901	120,230
Other assets	7,425	7,916
Total assets	1,029,152	958,119
Junior subordinated debentures issued to VNB Capital Trust I	150,001	147,595
Other liabilities	18,971	26,594
Total liabilities	168,972	174,189
Fair Value [Member] | Recurring fair value measurements [Member] | U.S. Treasury securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	89,786	97,625
Fair Value [Member] | Recurring fair value measurements [Member] | U.S. government agency securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	55,808	45,762
Fair Value [Member] | Recurring fair value measurements [Member] | Obligations of states and political subdivisions [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	39,234	16,627
Fair Value [Member] | Recurring fair value measurements [Member] | Residential mortgage-backed securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	573,827	510,154
Fair Value [Member] | Recurring fair value measurements [Member] | Trust preferred securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	68,413	57,432
Fair Value [Member] | Recurring fair value measurements [Member] | Corporate and other debt securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	84,246	30,708
Fair Value [Member] | Recurring fair value measurements [Member] | Equity securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	47,342	49,508
Fair Value [Member] | Non-recurring fair value measurements [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Collateral dependent impaired loans	41,835	65,231
Loan servicing rights	5,558	16,201
Foreclosed assets	7,192	33,251
Total	54,585	114,683
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Recurring fair value measurements [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	143,182	154,677
Trading securities
Loans held for sale
Other assets
Total assets	143,182	154,677
Junior subordinated debentures issued to VNB Capital Trust I	150,001	147,595
Other liabilities
Total liabilities	150,001	147,595
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Recurring fair value measurements [Member] | U.S. Treasury securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	89,786	97,625
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Recurring fair value measurements [Member] | U.S. government agency securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Recurring fair value measurements [Member] | Obligations of states and political subdivisions [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Recurring fair value measurements [Member] | Residential mortgage-backed securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Recurring fair value measurements [Member] | Trust preferred securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Recurring fair value measurements [Member] | Corporate and other debt securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	26,721	28,444
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Recurring fair value measurements [Member] | Equity securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	26,675	28,608
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Non-recurring fair value measurements [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Collateral dependent impaired loans
Loan servicing rights
Foreclosed assets
Total
Significant Other Observable Inputs (Level 2) [Member] | Recurring fair value measurements [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	736,362	581,465
Trading securities	14,170	22,157
Loans held for sale	48,901	120,230
Other assets	7,425	7,916
Total assets	806,858	731,768
Junior subordinated debentures issued to VNB Capital Trust I
Other liabilities	18,971	26,594
Total liabilities	18,971	26,594
Significant Other Observable Inputs (Level 2) [Member] | Recurring fair value measurements [Member] | U.S. Treasury securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities
Significant Other Observable Inputs (Level 2) [Member] | Recurring fair value measurements [Member] | U.S. government agency securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	55,808	45,762
Significant Other Observable Inputs (Level 2) [Member] | Recurring fair value measurements [Member] | Obligations of states and political subdivisions [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	39,234	16,627
Significant Other Observable Inputs (Level 2) [Member] | Recurring fair value measurements [Member] | Residential mortgage-backed securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	545,687	478,783
Significant Other Observable Inputs (Level 2) [Member] | Recurring fair value measurements [Member] | Trust preferred securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	17,441	17,129
Significant Other Observable Inputs (Level 2) [Member] | Recurring fair value measurements [Member] | Corporate and other debt securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	57,525	2,264
Significant Other Observable Inputs (Level 2) [Member] | Recurring fair value measurements [Member] | Equity securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	20,667	20,900
Significant Other Observable Inputs (Level 2) [Member] | Non-recurring fair value measurements [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Collateral dependent impaired loans
Loan servicing rights
Foreclosed assets
Total
Significant Unobservable Inputs (Level 3) [Member] | Recurring fair value measurements [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	79,112	71,674
Trading securities
Loans held for sale
Other assets
Total assets	79,112	71,674
Junior subordinated debentures issued to VNB Capital Trust I
Other liabilities
Total liabilities
Significant Unobservable Inputs (Level 3) [Member] | Recurring fair value measurements [Member] | U.S. Treasury securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities
Significant Unobservable Inputs (Level 3) [Member] | Recurring fair value measurements [Member] | U.S. government agency securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities
Significant Unobservable Inputs (Level 3) [Member] | Recurring fair value measurements [Member] | Obligations of states and political subdivisions [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities
Significant Unobservable Inputs (Level 3) [Member] | Recurring fair value measurements [Member] | Residential mortgage-backed securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	28,140	31,371
Significant Unobservable Inputs (Level 3) [Member] | Recurring fair value measurements [Member] | Trust preferred securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	50,972	40,303
Significant Unobservable Inputs (Level 3) [Member] | Recurring fair value measurements [Member] | Corporate and other debt securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities
Significant Unobservable Inputs (Level 3) [Member] | Recurring fair value measurements [Member] | Equity securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities
Significant Unobservable Inputs (Level 3) [Member] | Non-recurring fair value measurements [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Collateral dependent impaired loans	41,835	65,231
Loan servicing rights	5,558	16,201
Foreclosed assets	7,192	33,251
Total	$ 54,585	$ 114,683