Fair Value Measurement - Carrying Value and Estimated Fair Values of Financial Instruments (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and cash equivalents, Carrying Value	$ 54,265	$ 46,880	$ 38,010	$ 45,887
Available for sale securities, Fair value	242,106	270,561
Held to maturity securities, Carrying Value	78,700	82,911
Loans held for sale at lower of cost or market, Carrying Value		211
Loans held for sale, at fair value	95,235	83,541
Loans, net, Carrying Value	2,148,942	1,999,877
FHLB stock, Carrying Value	19,144	19,324
Accrued interest receivable, Carrying Value	8,551	8,190
FHLB advances, Carrying Value	(95,025)	(356,536)
Advance payments by borrowers for taxes and insurance, Carrying Value	(16,494)	(25,038)
Accrued interest payable, Carrying Value	(1,177)	(1,097)
Held to maturity securities, Fair value	74,812	82,126
Reported Value Measurement [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and cash equivalents, Carrying Value	54,265	46,880
Available for sale securities, Fair value	242,106	270,561
Held to maturity securities, Carrying Value	78,700	82,911
Loans held for sale at lower of cost or market, Carrying Value		211
Loans held for sale, at fair value	95,235	83,541
Loans, net, Carrying Value	2,148,942	1,999,877
FHLB stock, Carrying Value	19,144	19,324
Accrued interest receivable, Carrying Value	8,551	8,190
Purchased certificate of deposit option, Carrying Value	459	809
Interest rate swaps, Carrying Value	21
Checking, savings and money market accounts, Carrying Value	(1,313,932)	(1,251,398)
Certificates of deposit, Carrying Value	(1,038,544)	(705,341)
FHLB advances, Carrying Value	(95,025)	(356,536)
Repurchase agreements and other, Carrying Value	(238)	(197)
Advance payments by borrowers for taxes and insurance, Carrying Value	(16,494)	(25,038)
Accrued interest payable, Carrying Value	(1,177)	(1,097)
Written certificate of deposit option, Carrying Value	(459)	(809)
Interest rate swaps, Carrying Value	(25)
Estimate of Fair Value Measurement [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and cash equivalents, Fair Value	54,265	46,880
Checking, savings and money market accounts, Fair Value	(1,313,932)	(1,251,398)
Advance payments by borrowers for taxes and insurance, Fair Value	(16,494)	(25,038)
Estimate of Fair Value Measurement [Member] \| Significant Other Observable Inputs (Level 2) [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available for sale securities, Fair value	242,106	270,561
Loans held for sale, at fair value	14,308	18,525
Held to maturity securities, Fair value	74,812	82,126
Loans held for sale at lower of cost or market, Fair Value		217
Accrued interest receivable, Fair Value	1,582	2,244
Purchased certificate of deposit option, Fair Value	459	809
Interest rate swaps	21
Certificates of deposit, Fair Value	(1,034,803)	(705,238)
FHLB advances, Fair Value	(94,949)	(356,521)
Repurchase agreements and other, Fair Value	(224)	(190)
Accrued interest payable, Fair Value	(1,177)	(1,097)
Written certificate of deposit option, Fair Value	(459)	(809)
Interest rate swaps, Fair Value	(25)
Estimate of Fair Value Measurement [Member] \| Significant Unobservable Inputs (Level 3) [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Loans held for sale, at fair value	80,927	65,016
Loans, net, Fair Value	2,117,982	1,990,289
Accrued interest receivable, Fair Value	$ 6,969	$ 5,946

Accrued interest receivable fair value.

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- Definition

Advance payments by borrowers for taxes and insurance fair value.

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Certificates of deposit option.

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Certificates of deposit at fair value.

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Checking savings and money market deposits.

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Checking savings and money market deposits fair value.

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Interest rate swaps assets at carrying value.

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Interest rate swaps liabilities at carrying value.

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Loans held for investment fair value disclosure.

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Loans held for sale at lower of cost or market fair value disclosure.

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Securities sold under agreements to repurchase and borrowings.

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Securities sold under agreements to repurchase and other borrowings fair value.

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Fair value portion of trade and related party payables and accrued expenses.

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Carrying amount of accumulated prepayments received by financial institutions from borrowers for taxes (for example, property taxes) and insurance (for example, property and catastrophe) which will periodically be remitted to the appropriate governmental agency or vendor on behalf of the borrower.

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Amount of borrowings as of the balance sheet date from the Federal Home Loan Bank, which are primarily used to cover shortages in the required reserve balance and liquidity shortages.

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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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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The sum of cash and cash equivalents plus Federal Funds Sold. Cash and cash equivalents consist of short term, highly liquid investments that are readily convertible to known amounts of cash and are so near their maturity that they present negligible risk of changes in value due to changes in interest rates -- usually with an original maturity less than 90 days.

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A savings certificate entitling the Entity (that is, bearer) to receive interest at an established maturity date, based upon a fixed interest rate. A certificate of deposit may be issued in any denomination. Certificates of deposit are generally issued by commercial banks and, therefore, insured by the FDIC (up to the prescribed limit). Certificates of deposit generally restrict holders from withdrawing funds on demand without the incurrence of penalties. Generally, only certificates of deposit with original maturities of three months or less qualify as cash equivalents. Original maturity means original maturity to the entity holding the investment. As a related example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three-years ago does not become a cash equivalent when its remaining maturity is three months.

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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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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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

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Federal Home Loan Bank (FHLB) stock represents an equity interest in a FHLB. It does not have a readily determinable fair value because its ownership is restricted and it lacks a market (liquidity).

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Amount of investment in debt security measured at amortized cost (held-to-maturity).

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Fair value of investment in debt security measured at amortized cost (held-to-maturity).

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Amount of interest-bearing domestic certificate of deposit liabilities.

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

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Fair value as of the balance sheet date of interest rate derivative assets, which includes all such derivative instruments in hedging and nonhedging relationships that are recognized as assets.

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No definition available.

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Fair value as of the balance sheet date of interest rate derivative liabilities, which includes all such derivative instruments in hedging and nonhedging relationships that are recognized as liabilities.

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No definition available.

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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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Amount after allowance and deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements and loans held for sale.

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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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Amount, after allowance for bad debt, of loan receivables held-for-sale that are not part of a disposal group. Excludes loans and leases covered under loss sharing agreements and loans classified as debt securities.

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Amount of time deposit liabilities, including certificates of deposit.

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