FAIR VALUE MEASUREMENT AND DISCLOSURE (Schedule of Valuation Methodology and Unobservable Inputs) (Details) - Fair Value, Inputs, Level 3 [Member] - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2018	Dec. 31, 2017
Impaired Loans Partially Charged Off
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	$ 18	$ 86
Impaired Loans Partially Charged Off \| Market Approach Valuation Technique \| Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Management adjustment of appraisal	0.00%	0.00%
Estimated selling cost	10.00%	0.00%
Impaired Loans Partially Charged Off \| Market Approach Valuation Technique \| Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Management adjustment of appraisal	0.00%	50.00%
Estimated selling cost	10.00%	10.00%
Impaired Loans Partially Charged Off \| Market Approach Valuation Technique \| Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Management adjustment of appraisal	0.00%	18.00%
Estimated selling cost	10.00%	6.00%
Impaired Loans Specifically Reserved
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	$ 3,582	$ 3,610
Impaired Loans Specifically Reserved \| Market Approach Valuation Technique \| Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Management adjustment of appraisal	0.00%	0.00%
Estimated selling cost	0.00%	10.00%
Impaired Loans Specifically Reserved \| Market Approach Valuation Technique \| Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Management adjustment of appraisal	0.00%	0.00%
Estimated selling cost	0.00%	10.00%
Impaired Loans Specifically Reserved \| Market Approach Valuation Technique \| Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Management adjustment of appraisal	0.00%	0.00%
Estimated selling cost	0.00%	10.00%
Other real estate owned
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	$ 130	$ 130
Other real estate owned \| Market Approach Valuation Technique \| Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Management adjustment of appraisal	20.00%	20.00%
Estimated selling cost	10.00%	10.00%
Other real estate owned \| Market Approach Valuation Technique \| Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Management adjustment of appraisal	20.00%	20.00%
Estimated selling cost	10.00%	10.00%
Other real estate owned \| Market Approach Valuation Technique \| Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Management adjustment of appraisal	20.00%	20.00%
Estimated selling cost	10.00%	10.00%

Fair Value Inputs, Estimated Selling Cost

No definition available.

Name:	cac_FairValueInputsEstimatedSellingCost
Namespace Prefix:	cac_
Data Type:	num:percentItemType
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://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=66048111&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_FairValueInputsAssetsQuantitativeInformationLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Interest rate used to find the present value of an amount to be paid or received in the future as an input to measure fair value. For example, but not limited to, weighted average cost of capital (WACC), cost of capital, cost of equity and cost of debt.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

+ Details

Name:	us-gaap_FairValueInputsDiscountRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Details

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

- Details

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

- Details

Name:	us-gaap_ValuationTechniqueAxis=us-gaap_MarketApproachValuationTechniqueMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_WeightedAverageMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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