Loans - Loans by Class Modified as TDRs (Detail) $ in Thousands	12 Months Ended
Dec. 31, 2017 USD ($) Loan	Dec. 31, 2016 USD ($) Loan	Dec. 31, 2015 USD ($) Loan
Financing Receivable Modifications [Line Items]
Number of Loans \| Loan	6	16	29
Pre-Modification Outstanding Recorded Investment	$ 1,803	$ 7,124	$ 2,155
Post-Modification Recorded Investment	$ 1,844	$ 7,175	$ 2,190
Commercial Loans [Member]
Financing Receivable Modifications [Line Items]
Number of Loans \| Loan	2	4
Pre-Modification Outstanding Recorded Investment	$ 1,379	$ 6,134
Post-Modification Recorded Investment	$ 1,379	$ 6,140
Commercial Loans [Member] \| Nonresidential [Member]
Financing Receivable Modifications [Line Items]
Number of Loans \| Loan	2	4
Pre-Modification Outstanding Recorded Investment	$ 1,379	$ 6,134
Post-Modification Recorded Investment	$ 1,379	$ 6,140
Residential Mortgage Loans [Member]
Financing Receivable Modifications [Line Items]
Number of Loans \| Loan	3	8	14
Pre-Modification Outstanding Recorded Investment	$ 309	$ 812	$ 1,283
Post-Modification Recorded Investment	$ 350	$ 853	$ 1,337
Residential Mortgage Loans [Member] \| One-to Four-Family [Member]
Financing Receivable Modifications [Line Items]
Number of Loans \| Loan	3	8	14
Pre-Modification Outstanding Recorded Investment	$ 309	$ 812	$ 1,283
Post-Modification Recorded Investment	$ 350	$ 853	$ 1,337
Consumer Loans [Member]
Financing Receivable Modifications [Line Items]
Number of Loans \| Loan	1	4	15
Pre-Modification Outstanding Recorded Investment	$ 115	$ 178	$ 872
Post-Modification Recorded Investment	$ 115	$ 182	$ 853
Consumer Loans [Member] \| Home Equity [Member]
Financing Receivable Modifications [Line Items]
Number of Loans \| Loan		4	14
Pre-Modification Outstanding Recorded Investment		$ 178	$ 844
Post-Modification Recorded Investment		$ 182	$ 845
Consumer Loans [Member] \| Recreational Vehicle [Member]
Financing Receivable Modifications [Line Items]
Number of Loans \| Loan	1
Pre-Modification Outstanding Recorded Investment	$ 115
Post-Modification Recorded Investment	$ 115
Consumer Loans [Member] \| Other [Member]
Financing Receivable Modifications [Line Items]
Number of Loans \| Loan			1
Pre-Modification Outstanding Recorded Investment			$ 28
Post-Modification Recorded Investment			$ 8

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

+ References

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