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Fair Value Measurement - Quantitative Information about Level 3 Fair Value Measurements (Detail) - Assets Measured at Fair Value on a Nonrecurring Basis [Member] - (Level 3) [Member]
12 Months Ended
Dec. 31, 2020
USD ($)
Dec. 31, 2019
USD ($)
Impaired Loans [Member]    
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]    
Fair Value $ 1,000 $ 1,000
Valuation Technique [Extensible List] civb:AppraisalOfCollateralMember civb:AppraisalOfCollateralMember
Impaired Loans [Member] | Measurement Input, Appraised Value [Member]    
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]    
Unobservable Input   30
Impaired Loans [Member] | Measurement Input, Appraised Value [Member] | Minimum [Member]    
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]    
Unobservable Input 0  
Impaired Loans [Member] | Measurement Input, Appraised Value [Member] | Maximum [Member]    
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]    
Unobservable Input 30  
Impaired Loans [Member] | Measurement Input, Appraised Value [Member] | Weighted Average [Member]    
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]    
Unobservable Input 19 30
Impaired Loans [Member] | Measurement Input Holding Period [Member]    
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]    
Impaired loans, Term 23 months 22 months
Impaired Loans [Member] | Measurement Input Holding Period [Member] | Weighted Average [Member]    
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]    
Impaired loans, Term 23 months 22 months
Other Real Estate Owned [Member]    
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]    
Fair Value $ 31,000  
Valuation Technique [Extensible List] civb:AppraisalOfCollateralMember  
Other Real Estate Owned [Member] | Measurement Input, Appraised Value [Member]    
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]    
Unobservable Input 10  
Other Real Estate Owned [Member] | Measurement Input, Appraised Value [Member] | Weighted Average [Member]    
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]    
Unobservable Input 10