Mortgage Servicing Rights - Fair Value of Mortgage Servicing Rights (Detail) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Servicing Assets at Fair Value [Line Items]
Contractually specified servicing fees, late fees and ancillary fees earned	$ 511	$ 526	$ 1,028	$ 1,047
Mortgage Servicing Rights [Member]
Servicing Assets at Fair Value [Line Items]
Balance at beginning of period	6,953	6,860	6,687	6,595
Additions	104	193	259	471
Change in fair value	(36)	(457)	75	(470)
Balance at end of period	7,021	6,596	$ 7,021	$ 6,596
Measurement Input, Constant Prepayment Rate [Member]
Servicing Assets at Fair Value [Line Items]
Fair Value Of Mortgage Servicing Rights Weighted Average			7.40%	8.70%
Measurement Input, Discount Rate [Member]
Servicing Assets at Fair Value [Line Items]
Fair Value Of Mortgage Servicing Rights Weighted Average			12.50%	14.00%
Loans [Member]
Servicing Assets at Fair Value [Line Items]
Balance at beginning of period	806,178	822,506	$ 811,065	$ 816,623
Balance at end of period	$ 801,817	$ 822,549	$ 801,817	$ 822,549

Assumptions In Measuring Fair Value Of Mortgage Servicing Rights Weighted Average.

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- Definition

Amount of contractually specified servicing fee, late fee, and ancillary fee recognized as income for servicing asset and servicing liability.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 50
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=68078379&loc=d3e122596-111746

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- Definition

The value of new servicing assets, subsequently measured at fair value, acquired or created during the current period through purchases or from transfers of financial assets.

+ References

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-Publisher FASB
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-Topic 860
-SubTopic 50
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-URI http://asc.fasb.org/extlink&oid=68078379&loc=d3e122625-111746

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- Definition

Fair value of an asset representing net future revenue from contractually specified servicing fees, late charges, and other ancillary revenues, in excess of future costs related to servicing arrangements.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 50
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6469459&loc=d3e122501-111745

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- Definition

The increase (decrease) in the fair value of servicing assets that are subsequently measured at fair value.

+ References

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-SubTopic 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

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