Carrying Amount and Fair Value of Company's Financial Instruments (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Assets
Available-for-sale securities	$ 326,117us-gaap_AvailableForSaleSecurities	$ 519,820us-gaap_AvailableForSaleSecurities
Held-to-maturity securities	57,889	579
FDIC indemnification asset	27,900us-gaap_FDICIndemnificationAsset	34,691us-gaap_FDICIndemnificationAsset	48,149us-gaap_FDICIndemnificationAsset
Accrued interest receivable	6,315us-gaap_InterestReceivable	7,521us-gaap_InterestReceivable
Derivative financial assets	5us-gaap_DerivativeAssets	84us-gaap_DerivativeAssets
Liabilities
Derivative financial liabilities	214us-gaap_DerivativeLiabilities	41us-gaap_DerivativeLiabilities
Carrying (Reported) Amount, Fair Value Disclosure
Assets
Cash and cash equivalents	237,660	56,567
Available-for-sale securities	326,117	519,820
Held-to-maturity securities	57,948	568
Loans held for sale	1,792	883
Loans held for investment less allowance	1,669,189	1,686,644
FDIC indemnification asset	27,900	34,691
Accrued interest receivable	6,315	7,521
Derivative financial assets	5	84
Deferred compensation assets	3,380	4,200
Liabilities
Securities sold under agreements to repurchase	121,742	118,308
Accrued interest payable	1,668	2,169
FHLB and other borrowings	107,999	166,088
Derivative financial liabilities	214	41
Deferred compensation liabilities	3,380	4,200
Carrying (Reported) Amount, Fair Value Disclosure \| Demand Deposits
Liabilities
Deposits Fair Value	417,729	339,680
Carrying (Reported) Amount, Fair Value Disclosure \| Interest-bearing Deposits
Liabilities
Deposits Fair Value	353,874	361,821
Carrying (Reported) Amount, Fair Value Disclosure \| Savings Deposits
Liabilities
Deposits Fair Value	525,478	524,010
Carrying (Reported) Amount, Fair Value Disclosure \| Bank Time Deposits
Liabilities
Deposits Fair Value	703,678	725,231
Estimate of Fair Value, Fair Value Disclosure
Assets
Cash and cash equivalents	237,660	56,567
Available-for-sale securities	326,117	519,820
Held-to-maturity securities	57,889	579
Loans held for sale	1,790	883
Loans held for investment less allowance	1,738,553	1,655,430
FDIC indemnification asset	18,040	34,691
Accrued interest receivable	6,315	7,521
Derivative financial assets	5	84
Deferred compensation assets	3,380	4,200
Liabilities
Securities sold under agreements to repurchase	123,114	121,320
Accrued interest payable	1,668	2,169
FHLB and other borrowings	116,599	178,031
Derivative financial liabilities	214	41
Deferred compensation liabilities	3,380	4,200
Estimate of Fair Value, Fair Value Disclosure \| Demand Deposits
Liabilities
Deposits Fair Value	417,729	339,680
Estimate of Fair Value, Fair Value Disclosure \| Interest-bearing Deposits
Liabilities
Deposits Fair Value	353,874	361,821
Estimate of Fair Value, Fair Value Disclosure \| Savings Deposits
Liabilities
Deposits Fair Value	525,478	524,010
Estimate of Fair Value, Fair Value Disclosure \| Bank Time Deposits
Liabilities
Deposits Fair Value	704,590	728,999
Level 1
Assets
Cash and cash equivalents	237,660	56,567
Available-for-sale securities	221	251
Deferred compensation assets	3,380	4,200
Liabilities
Deferred compensation liabilities	3,380	4,200
Level 2
Assets
Available-for-sale securities	325,896	519,569
Held-to-maturity securities	57,889	579
Loans held for sale	1,790	883
Loans held for investment less allowance	3,406	4,404
Accrued interest receivable	6,315	7,521
Derivative financial assets	5	84
Liabilities
Securities sold under agreements to repurchase	123,114	121,320
Accrued interest payable	1,668	2,169
FHLB and other borrowings	116,599	178,031
Derivative financial liabilities	214	41
Level 2 \| Demand Deposits
Liabilities
Deposits Fair Value	417,729	339,680
Level 2 \| Interest-bearing Deposits
Liabilities
Deposits Fair Value	353,874	361,821
Level 2 \| Savings Deposits
Liabilities
Deposits Fair Value	525,478	524,010
Level 2 \| Bank Time Deposits
Liabilities
Deposits Fair Value	704,590	728,999
Level 3
Assets
Loans held for investment less allowance	1,735,147	1,651,026
FDIC indemnification asset	$ 18,040	$ 34,691

Deferred compensation assets fair value.

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Deferred compensation liabilities fair value.

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

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Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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Fair value portion of deposit liabilities held by the entity, including, but not limited to, foreign and domestic, interest and noninterest bearing, demand deposits, saving deposits, negotiable orders of withdrawal (NOW) and time deposits.

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Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

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Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

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Carrying amount of receivable assets originating from the indemnification agreement with the Federal Deposit Insurance Corporation (FDIC), in which the FDIC is to partially cover losses.

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Fair value portion of borrowing from Federal Home Loan Bank (FHLBank).

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Fair value of investments in debt securities classified as held-to-maturity.

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Amount of interest payable on debt, including, but not limited to, trade payables.

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Carrying amount as of the balance sheet date of interest earned but not received. Also called accrued interest or accrued interest receivable.

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Fair value portion of loans held-for-sale including, but not limited to, mortgage loans and finance receivables.

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Fair value portion of loan receivable, including, but not limited to, mortgage loans held for investment, finance receivables held for investment, policy loans on insurance contracts.

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Fair value portion of securities that an entity sells and agrees to repurchase at a specified date for a specified price.

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