Assets and Liabilities Measured at Fair Value on Recurring and Non-Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012		Dec. 31, 2011
Estimate of Fair Value, Fair Value Disclosure | Recurring fair value measurements
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Corporate and other debt securities	$ 673,911		$ 566,520
Trading securities	22,104		21,938
Loans held for sale	149,067	[1]	25,169	[1]
Other assets	11,918	[2]	5,211	[2]
Total assets	857,000		618,838
Junior subordinated debentures issued to VNB Capital Trust I	149,708	[3]	160,478	[3]
Other liabilities	31,227	[2]	21,854	[2]
Total liabilities	180,935		182,332
Estimate of Fair Value, Fair Value Disclosure | Recurring fair value measurements | U.S. government agency securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Corporate and other debt securities	47,577		90,748
Estimate of Fair Value, Fair Value Disclosure | Recurring fair value measurements | Obligations of states and political subdivisions
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Corporate and other debt securities	16,472		20,214
Estimate of Fair Value, Fair Value Disclosure | Recurring fair value measurements | Residential mortgage-backed securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Corporate and other debt securities	470,727		310,137
Estimate of Fair Value, Fair Value Disclosure | Recurring fair value measurements | Trust preferred securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Corporate and other debt securities	58,595		70,425
Estimate of Fair Value, Fair Value Disclosure | Recurring fair value measurements | Corporate and other debt securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Corporate and other debt securities	31,387		33,043
Estimate of Fair Value, Fair Value Disclosure | Recurring fair value measurements | Equity securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Corporate and other debt securities	49,153		41,953
Estimate of Fair Value, Fair Value Disclosure | Non-recurring fair value measurements
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Collateral dependent impaired loans	71,377	[4]	66,854	[4]
Loan servicing rights	12,814		9,078
Foreclosed assets	25,861		15,874
Total	110,052		91,806
Quoted Prices in Active Markets for Identical Assets (Level 1) | Recurring fair value measurements
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Corporate and other debt securities	56,166		73,685
Total assets	56,166		73,685
Junior subordinated debentures issued to VNB Capital Trust I	149,708	[3]	160,478	[3]
Total liabilities	149,708		160,478
Quoted Prices in Active Markets for Identical Assets (Level 1) | Recurring fair value measurements | Trust preferred securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Corporate and other debt securities			19,576
Quoted Prices in Active Markets for Identical Assets (Level 1) | Recurring fair value measurements | Corporate and other debt securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Corporate and other debt securities	28,895		30,603
Quoted Prices in Active Markets for Identical Assets (Level 1) | Recurring fair value measurements | Equity securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Corporate and other debt securities	27,271		23,506
Significant Other Observable Inputs (Level 2) | Recurring fair value measurements
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Corporate and other debt securities	535,466		415,524
Trading securities	22,104		21,938
Loans held for sale	149,067	[1]	25,169	[1]
Other assets	11,918	[2]	5,211	[2]
Total assets	718,555		467,842
Other liabilities	31,227	[2]	21,854	[2]
Total liabilities	31,227		21,854
Significant Other Observable Inputs (Level 2) | Recurring fair value measurements | U.S. government agency securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Corporate and other debt securities	47,577		90,748
Significant Other Observable Inputs (Level 2) | Recurring fair value measurements | Obligations of states and political subdivisions
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Corporate and other debt securities	16,472		20,214
Significant Other Observable Inputs (Level 2) | Recurring fair value measurements | Residential mortgage-backed securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Corporate and other debt securities	429,227		259,977
Significant Other Observable Inputs (Level 2) | Recurring fair value measurements | Trust preferred securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Corporate and other debt securities	17,816		23,698
Significant Other Observable Inputs (Level 2) | Recurring fair value measurements | Corporate and other debt securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Corporate and other debt securities	2,492		2,440
Significant Other Observable Inputs (Level 2) | Recurring fair value measurements | Equity securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Corporate and other debt securities	21,882		18,447
Significant Unobservable Inputs (Level 3) | Recurring fair value measurements
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Corporate and other debt securities	82,279		77,311
Total assets	82,279		77,311
Significant Unobservable Inputs (Level 3) | Recurring fair value measurements | Residential mortgage-backed securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Corporate and other debt securities	41,500		50,160
Significant Unobservable Inputs (Level 3) | Recurring fair value measurements | Trust preferred securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Corporate and other debt securities	40,779		27,151
Significant Unobservable Inputs (Level 3) | Non-recurring fair value measurements
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Collateral dependent impaired loans	71,377	[4]	66,854	[4]
Loan servicing rights	12,814		9,078
Foreclosed assets	25,861		15,874
Total	$ 110,052		$ 91,806

[1] Loans held for sale (which consist of residential mortgages) are carried at fair value and had contractual unpaid principal balances totaling approximately $141.4 million and $24.3 million at September 30, 2012 and December 31, 2011, respectively.

[2] Derivative financial instruments are included in this category.

[3] The junior subordinated debentures had contractual unpaid principal obligations totaling $146.7 million and $157.0 million at September 30, 2012 and December 31, 2011, respectively.

[4] Excludes covered loans acquired in the FDIC-assisted transactions completed in the first quarter of 2010 and other purchased credit-impaired loans acquired in the first quarter of 2012.