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] - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Impaired Loans [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Estimate	$ 1,350	$ 1,040
Valuation Technique [Extensible List]	civb:AppraisalOfCollateralMember	civb:AppraisalOfCollateralMember
Impaired Loans [Member] | Minimum [Member] | Measurement Input, Appraised Value
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Assumptions, Appraisal adjustments	10.00%	0.00%
Impaired Loans [Member] | Minimum [Member] | Measurement Input Liquidation Expense
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Assumptions, Liquidation expense	0.00%	0.00%
Impaired Loans [Member] | Minimum [Member] | Measurement Input Holding Period
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Assumptions, Holding period	0 months	0 months
Impaired Loans [Member] | Maximum [Member] | Measurement Input, Appraised Value
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Assumptions, Appraisal adjustments	38.00%	30.00%
Impaired Loans [Member] | Maximum [Member] | Measurement Input Liquidation Expense
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Assumptions, Liquidation expense	10.00%	10.00%
Impaired Loans [Member] | Maximum [Member] | Measurement Input Holding Period
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Assumptions, Holding period	30 months	30 months
Impaired Loans [Member] | Weighted Average [Member] | Measurement Input, Appraised Value
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Assumptions, Appraisal adjustments	30.00%	16.00%
Impaired Loans [Member] | Weighted Average [Member] | Measurement Input Liquidation Expense
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Assumptions, Liquidation expense	3.00%	8.00%
Impaired Loans [Member] | Weighted Average [Member] | Measurement Input Holding Period
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Assumptions, Holding period	21 months	20 months
Other Real Estate Owned
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Estimate		$ 16
Other Real Estate Owned, Valuation Technique [Extensible List]		civb:AppraisalOfCollateralMember
Other Real Estate Owned | Minimum [Member] | Measurement Input, Appraised Value
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Assumptions, Appraisal adjustments		10.00%
Other Real Estate Owned | Minimum [Member] | Measurement Input Liquidation Expense
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Assumptions, Liquidation expense		0.00%
Other Real Estate Owned | Maximum [Member] | Measurement Input, Appraised Value
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Assumptions, Appraisal adjustments		30.00%
Other Real Estate Owned | Maximum [Member] | Measurement Input Liquidation Expense
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Assumptions, Liquidation expense		10.00%
Other Real Estate Owned | Weighted Average [Member] | Measurement Input, Appraised Value
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Assumptions, Appraisal adjustments		10.00%
Other Real Estate Owned | Weighted Average [Member] | Measurement Input Liquidation Expense
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Assumptions, Liquidation expense		10.00%