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Allowance for Loan Losses - Narrative (Detail)	3 Months Ended		6 Months Ended
	Jun. 30, 2018 USD ($) Contract	Jun. 30, 2017 USD ($) Contract	Jun. 30, 2018 USD ($) Contract	Jun. 30, 2017 USD ($) Contract	Dec. 31, 2017 USD ($)
Allowance For Loan Losses [Line Items]
TDRs performing under the restructured terms	$ 321,000		$ 321,000		$ 333,000
Loans modified under TDRs | Contract	0	0	0	0
Troubled debt restructuring loan subsequent default	$ 0	$ 0	$ 0	$ 0
Troubled debt restructuring loan subsequent default period			90 days
Performing financing receivable
Allowance For Loan Losses [Line Items]
TDRs performing under the restructured terms	$ 273,000		$ 273,000		$ 282,000

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Allowance For Loan Losses [Line Items]

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Financing receivable modification as troubled debt restructuring that subsequently defaulted.

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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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The amount of the outstanding recorded investment related to 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 40
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=82895541&loc=d3e18845-111554

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Amount of investment related to financing receivables modified by troubled debt restructurings within the previous 12 months, for which there was a payment default.

+ References

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