Derivative Financial Instruments - Summary of Outstanding Notional Balances and Fair Values of Outstanding Derivative Positions (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017
IRLCs [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Outstanding Notional Balance	$ 48,311	$ 37,589	$ 53,911
Asset Derivative Fair Value	715	500	440
Liability Derivative Fair Value	0	$ 0	$ 0
Forward Mortgage-Backed Securities Trades [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Outstanding Notional Balance	42,500
Asset Derivative Fair Value	143
Liability Derivative Fair Value	$ 0

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

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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.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 7
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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-Section 50
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- Definition

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

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
-Topic 860
-SubTopic 20
-Section 50
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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.

+ References

No definition available.

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