Fair Value Measurements - Fair Value on Balance Sheet (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Financial assets:
Securities available for sale, at fair value	$ 1,034,758	$ 710,570
Securities held to maturity	254,841	236,125
Loans held-for-sale amount	8,081
Loans receivable, net	8,081	0
Derivative asset, gross	865	490
Financial liabilities:
Derivative liability, gross	3,467	203
Quoted prices in active markets for identical assets (Level 1)
Financial assets:
Cash and cash equivalents	42,201	65,498
Securities available for sale, at fair value		42,831
Securities held to maturity	23,241	8,344
Federal Home Loan Bank stock	0	0
Loans held-for-sale amount
Loans receivable, net	0	0
Derivative asset, gross	0	0
Financial liabilities:
Deposits	0	0
Borrowings	0	0
Derivative liability, gross	0	0
Significant other observable inputs (Level 2)
Financial assets:
Cash and cash equivalents	0	0
Securities available for sale, at fair value		667,739
Securities held to maturity	254,841	227,781
Federal Home Loan Bank stock	58,938	44,664
Loans held-for-sale amount	8,081
Loans receivable, net	0	0
Derivative asset, gross	865	490
Financial liabilities:
Deposits	4,402,336	3,959,460
Borrowings	1,185,007	925,032
Derivative liability, gross	3,467	203
Significant unobservable inputs (Level 3)
Financial assets:
Cash and cash equivalents	0	0
Securities available for sale, at fair value	0	0
Securities held to maturity	0	0
Federal Home Loan Bank stock	0	0
Loans held-for-sale amount	0
Loans receivable, net	4,841,830	4,367,945
Derivative asset, gross	0	0
Financial liabilities:
Deposits	0	0
Borrowings	0	0
Derivative liability, gross	0	0
Carrying value
Financial assets:
Cash and cash equivalents	42,201	65,498
Securities available for sale, at fair value	1,034,758	710,570
Securities held to maturity	262,143	239,618
Federal Home Loan Bank stock	58,938	44,664
Loans held-for-sale amount	8,081
Loans receivable, net	4,979,182	4,400,470
Derivative asset, gross		490
Financial liabilities:
Deposits	4,413,873	4,263,315
Borrowings	1,189,180	929,057
Derivative liability, gross		203
Total fair value
Financial assets:
Cash and cash equivalents	42,201	65,498
Securities available for sale, at fair value	1,034,758	710,570
Securities held to maturity	254,841	236,125
Federal Home Loan Bank stock	58,938	44,664
Loans held-for-sale amount	8,081
Loans receivable, net	4,841,830	4,367,945
Derivative asset, gross	865	490
Financial liabilities:
Deposits	4,402,336	3,959,460
Borrowings	1,185,007	925,032
Derivative liability, gross	$ 3,467	$ 203

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 debt instrument payable, including, but not limited to, notes payable and loans payable.

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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 of liability associated with 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.

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Fair value, before 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 elected not to be offset. Excludes assets not subject to a master netting arrangement.

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

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Fair value portion of investments in Federal Home Loan Bank (FHLBank) stock.

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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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The face amount of loans that will be sold to other entities.

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