Fair Value of Financial Instrument - Carrying Amount and Estimated Fair Value of Financial Instruments (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014	Dec. 31, 2013
Financial assets:
Cash and due from banks	$ 80,142us-gaap_CashAndDueFromBanks	$ 78,036us-gaap_CashAndDueFromBanks	$ 71,387us-gaap_CashAndDueFromBanks	$ 62,955us-gaap_CashAndDueFromBanks
Federal funds sold and interest-bearing accounts	126,157us-gaap_FederalFundsSold	92,323us-gaap_FederalFundsSold	48,677us-gaap_FederalFundsSold
FDIC loss-share receivable	23,312us-gaap_FDICIndemnificationAsset	31,351us-gaap_FDICIndemnificationAsset	53,181us-gaap_FDICIndemnificationAsset	65,441us-gaap_FDICIndemnificationAsset
Financial liabilities:
Other borrowings	43,851us-gaap_OtherBorrowings	78,881us-gaap_OtherBorrowings	59,677us-gaap_OtherBorrowings
Subordinated deferrable interest debentures	65,567us-gaap_SubordinatedDebt	65,325us-gaap_SubordinatedDebt	55,628us-gaap_SubordinatedDebt
Carrying Value [Member]
Financial assets:
Cash and due from banks	80,142	78,026	71,387
Federal funds sold and interest-bearing accounts	126,157	92,323	48,677
Loans, net	2,837,538	2,783,763	2,441,348
FDIC loss-share receivable	23,312	31,351	53,181
Accrued interest receivable	15,332	17,023	13,849
Financial liabilities:
Deposits	3,480,231	3,431,149	3,010,647
Securities sold under agreements to repurchase	55,520	73,310	49,974
Other borrowings	43,851	78,881	59,677
Accrued interest payable	1,177	1,382	1,357
Subordinated deferrable interest debentures	65,567	65,325	55,628
Fair Value [Member]
Financial assets:
Cash and due from banks	80,142	78,026	71,387
Federal funds sold and interest-bearing accounts	126,157	92,323	48,677
Loans, net	2,885,524	2,785,627	2,461,372
FDIC loss-share receivable	9,990	18,764	39,930
Accrued interest receivable	15,332	17,023	13,849
Financial liabilities:
Deposits	3,481,470	3,432,059	3,011,383
Securities sold under agreements to repurchase	55,520	73,310	49,974
Other borrowings	43,851	78,881	59,677
Accrued interest payable	1,177	1,382	1,357
Subordinated deferrable interest debentures	47,055	46,564	36,504
Fair Value [Member] \| Level 1 [Member]
Financial assets:
Cash and due from banks	80,142	78,026	71,387
Federal funds sold and interest-bearing accounts	126,157	92,323	48,677
Accrued interest receivable	15,332	17,023	13,849
Financial liabilities:
Securities sold under agreements to repurchase	55,520	73,310	49,974
Accrued interest payable	1,177	1,382	1,357
Fair Value [Member] \| Level 2 [Member]
Financial liabilities:
Deposits	3,481,470	3,432,059	3,011,383
Other borrowings	43,851	78,881	59,677
Subordinated deferrable interest debentures	47,055	46,564	36,504
Fair Value [Member] \| Level 3 [Member]
Financial assets:
Loans, net	2,885,524	2,785,627	2,461,372
FDIC loss-share receivable	$ 9,990	$ 18,764	$ 39,930

Accrued Interest Payable

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Accrued Interest Receivable

+ References

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- Definition

For banks and other depository institutions: Includes cash on hand (currency and coin), cash items in process of collection, noninterest bearing deposits due from other financial institutions (including corporate credit unions), and noninterest bearing balances with the Federal Reserve Banks, Federal Home Loan Banks and central banks.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Cash

-URI http://asc.fasb.org/extlink&oid=6506951

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-Publisher FASB

-Name Accounting Standards Codification

-Glossary Cash Equivalents

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.1)

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-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 1, 2, 3

-Article 9

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- Definition

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.

+ References

No definition available.

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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.

+ References

No definition available.

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- Definition

The amount outstanding of funds lent to other depository institutions, securities brokers, or securities dealers in the form of Federal Funds sold; for example, immediately available funds lent under agreements or contracts that mature in one business day or roll over under a continuing contract, regardless of the nature of the transaction or the collateral involved, excluding overnight lending for commercial and industrial purposes. Also include Federal Funds sold under agreements to resell on a gross basis, excluding (1) sales of term Federal Funds, (2) due bills representing purchases of securities or other assets by the reporting bank that have not yet been delivered and similar instruments, (3) resale agreements that mature in more than one business day involving assets other than securities, and (4) yield maintenance dollar repurchase agreements.

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- Definition

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

+ References

No definition available.

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- Definition

The carrying amount as of the balance sheet date for the aggregate of other miscellaneous borrowings owed by the reporting entity.

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- Definition

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

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 10

-URI http://asc.fasb.org/extlink&oid=35750535&loc=d3e13433-108611

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- Definition

Including the current and noncurrent portions, carrying value as of the balance sheet date of subordinated debt (with initial maturities beyond one year or beyond the operating cycle if longer). Subordinated debt places a lender in a lien position behind debt having a higher priority of repayment in liquidation of the entity's assets.

+ References

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.16)

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-Name Regulation S-X (SX)

-Number 210

-Section 03

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-Article 9

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

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-Subparagraph (SX 210.7-03.16)

-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

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-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 10

-Section F

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-Name Regulation S-X (SX)

-Number 210

-Section 02

-Article 5

-Subsection 19, 20, 22

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