Allowance for Loan Losses - Troubled Debt Restructurings (Detail) $ in Thousands	3 Months Ended
Mar. 31, 2019 USD ($) Branches SecurityLoan	Mar. 31, 2018 USD ($) Branches SecurityLoan
Financing Receivable, Modifications [Line Items]
Number \| SecurityLoan	4	3
Pre-mod outstanding principal balance	$ 299	$ 638
Post-mod outstanding principal balance	297	643
Financial impact due to TDR taken as additional provision	$ 1	$ 11
Number that defaulted during the period \| Branches	1	1
Recorded investment of TDRs that defaulted during the period	$ 7	$ 169
Mortgage Loans on Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number \| SecurityLoan	1	1
Pre-mod outstanding principal balance	$ 163	$ 384
Post-mod outstanding principal balance	$ 162	384
Financial impact due to TDR taken as additional provision		$ 11
Number that defaulted during the period \| Branches		1
Recorded investment of TDRs that defaulted during the period		$ 169
Consumer [Member]
Financing Receivable, Modifications [Line Items]
Number \| SecurityLoan	1	2
Pre-mod outstanding principal balance	$ 121	$ 254
Post-mod outstanding principal balance	120	$ 259
Financial impact due to TDR taken as additional provision	$ 1
Commercial Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Number \| SecurityLoan	2
Pre-mod outstanding principal balance	$ 15
Post-mod outstanding principal balance	$ 15
Number that defaulted during the period \| Branches	1
Recorded investment of TDRs that defaulted during the period	$ 7
Residential 1-4 Family [Member] \| Mortgage Loans on Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number \| SecurityLoan	1
Pre-mod outstanding principal balance	$ 163
Post-mod outstanding principal balance	$ 162
Home Equity Loans [Member] \| Consumer [Member]
Financing Receivable, Modifications [Line Items]
Number \| SecurityLoan	1	1
Pre-mod outstanding principal balance	$ 121	$ 121
Post-mod outstanding principal balance	120	$ 121
Financial impact due to TDR taken as additional provision	$ 1
Commercial [Member] \| Mortgage Loans on Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number \| SecurityLoan		1
Pre-mod outstanding principal balance		$ 384
Post-mod outstanding principal balance		384
Financial impact due to TDR taken as additional provision		$ 11
Number that defaulted during the period \| Branches		1
Recorded investment of TDRs that defaulted during the period		$ 169
Home Equity Lines of Credit [Member] \| Consumer [Member]
Financing Receivable, Modifications [Line Items]
Number \| SecurityLoan		1
Pre-mod outstanding principal balance		$ 133
Post-mod outstanding principal balance		$ 138

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Number of financing receivables that have been modified by troubled debt restructurings.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953676-111524

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Number of financing receivables that have been modified by troubled debt restructurings within the previous 12 months and for which there was a payment default.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 34
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953682-111524

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