Fair Value Measurement - Quantitative Information about Level 3 Fair Value Measurements (Detail) $ in Thousands	12 Months Ended
Dec. 31, 2018 USD ($)	Sep. 30, 2019 USD ($)
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value	$ 0	$ 0
Assets Measured at Fair Value on a Nonrecurring Basis [Member] \| Impaired Loans [Member] \| (Level 3) [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value	$ 1,803	$ 30
Valuation Technique [Extensible List]	civb:AppraisalOfCollateralMember	civb:AppraisalOfCollateralMember
Assets Measured at Fair Value on a Nonrecurring Basis [Member] \| Impaired Loans [Member] \| (Level 3) [Member] \| Minimum [Member] \| Measurement Input, Appraised Value
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Impaired loans, Unobservable Input	0	10
Assets Measured at Fair Value on a Nonrecurring Basis [Member] \| Impaired Loans [Member] \| (Level 3) [Member] \| Minimum [Member] \| Measurement Input Liquidation Expense [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Impaired loans, Unobservable Input	0
Assets Measured at Fair Value on a Nonrecurring Basis [Member] \| Impaired Loans [Member] \| (Level 3) [Member] \| Minimum [Member] \| Measurement Input Holding Period
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Impaired loans, Term	0 months
Assets Measured at Fair Value on a Nonrecurring Basis [Member] \| Impaired Loans [Member] \| (Level 3) [Member] \| Maximum [Member] \| Measurement Input, Appraised Value
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Impaired loans, Unobservable Input	30	30
Assets Measured at Fair Value on a Nonrecurring Basis [Member] \| Impaired Loans [Member] \| (Level 3) [Member] \| Maximum [Member] \| Measurement Input Liquidation Expense [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Impaired loans, Unobservable Input	10
Assets Measured at Fair Value on a Nonrecurring Basis [Member] \| Impaired Loans [Member] \| (Level 3) [Member] \| Maximum [Member] \| Measurement Input Holding Period
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Impaired loans, Term	30 months
Assets Measured at Fair Value on a Nonrecurring Basis [Member] \| Impaired Loans [Member] \| (Level 3) [Member] \| Weighted Average [Member] \| Measurement Input, Appraised Value
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Impaired loans, Unobservable Input	26	26
Assets Measured at Fair Value on a Nonrecurring Basis [Member] \| Impaired Loans [Member] \| (Level 3) [Member] \| Weighted Average [Member] \| Measurement Input Liquidation Expense [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Impaired loans, Unobservable Input	8
Assets Measured at Fair Value on a Nonrecurring Basis [Member] \| Impaired Loans [Member] \| (Level 3) [Member] \| Weighted Average [Member] \| Measurement Input Holding Period
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Impaired loans, Term	21 months

Servicing asset, term.

No definition available.

Name:	civb_ServicingAssetTerm
Namespace Prefix:	civb_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

+ Details

Name:	us-gaap_AssetsFairValueDisclosure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

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.

+ Details

Name:	us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Value of input used to measure servicing asset.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)(2)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

+ Details

Name:	us-gaap_ServicingAssetMeasurementInput
Namespace Prefix:	us-gaap_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant

- Definition

Indicates valuation technique for measuring servicing asset.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)(1)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

+ Details

Name:	us-gaap_ServicingAssetValuationTechniqueExtensibleList
Namespace Prefix:	us-gaap_
Data Type:	srt-types:extensibleListItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	us-gaap_FairValueByMeasurementFrequencyAxis=us-gaap_FairValueMeasurementsNonrecurringMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByAssetClassAxis=civb_ImpairedLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel3Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MeasurementInputTypeAxis=us-gaap_MeasurementInputAppraisedValueMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MeasurementInputTypeAxis=civb_MeasurementInputLiquidationExpenseMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MeasurementInputTypeAxis=civb_MeasurementInputHoldingPeriodMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_WeightedAverageMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: