Fair Value (Summary of Financial Assets and Liabilities Measured at Fair Value on Recurring Basis) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans Held-for-sale	$ 11,854	$ 4,403
Financial Assets:
AFS securities	918,118	910,692
Other Investments	13,649	14,679
Obligations of states and political subdivisions
Financial Assets:
AFS securities	118,083	93,752
Mortgage-backed securities issued or guaranteed by U.S. government sponsored enterprises [Member]
Financial Assets:
AFS securities	463,386	453,672
Collateralized mortgage obligations issued or guaranteed by U.S. government-sponsored enterprises
Financial Assets:
AFS securities	325,905	342,894
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans Held-for-sale	11,854	4,403
Financial Liabilities:
Junior subordinated debt interest rate swaps	8,187	5,682
Fair Value, Measurements, Recurring [Member] \| Obligations of states and political subdivisions
Financial Assets:
AFS securities	118,083
Fair Value, Measurements, Recurring [Member] \| Mortgage-backed securities issued or guaranteed by U.S. government sponsored enterprises [Member]
Financial Assets:
AFS securities	463,386	93,752
Fair Value, Measurements, Recurring [Member] \| Collateralized mortgage obligations issued or guaranteed by U.S. government-sponsored enterprises
Financial Assets:
AFS securities	325,905	453,672
Fair Value, Measurements, Recurring [Member] \| Corporate Bond Securities [Member]
Financial Assets:
AFS securities	10,744	342,894
Fair Value, Measurements, Recurring [Member] \| Equity Securities [Member]
Financial Assets:
AFS securities		20,374
Other Investments	1,674
Readily Available Market Prices (Level 1) [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans Held-for-sale	0	0
Readily Available Market Prices (Level 1) [Member] \| Fair Value, Measurements, Recurring [Member] \| Corporate Bond Securities [Member]
Financial Assets:
AFS securities	0	0
Readily Available Market Prices (Level 1) [Member] \| Fair Value, Measurements, Recurring [Member] \| Equity Securities [Member]
Financial Assets:
AFS securities	0	0
Observable Market Data (Level 2) [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans Held-for-sale	11,854	4,403
Financial Liabilities:
Junior subordinated debt interest rate swaps	8,187	5,682
Observable Market Data (Level 2) [Member] \| Fair Value, Measurements, Recurring [Member] \| Obligations of states and political subdivisions
Financial Assets:
AFS securities	118,083
Observable Market Data (Level 2) [Member] \| Fair Value, Measurements, Recurring [Member] \| Mortgage-backed securities issued or guaranteed by U.S. government sponsored enterprises [Member]
Financial Assets:
AFS securities	463,386	93,752
Observable Market Data (Level 2) [Member] \| Fair Value, Measurements, Recurring [Member] \| Collateralized mortgage obligations issued or guaranteed by U.S. government-sponsored enterprises
Financial Assets:
AFS securities	325,905	453,672
Observable Market Data (Level 2) [Member] \| Fair Value, Measurements, Recurring [Member] \| Corporate Bond Securities [Member]
Financial Assets:
AFS securities	10,744	342,894
Observable Market Data (Level 2) [Member] \| Fair Value, Measurements, Recurring [Member] \| Equity Securities [Member]
Financial Assets:
AFS securities		20,374
Other Investments	1,674
Company Determined Fair Value (Level 3) [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans Held-for-sale	0	0
Company Determined Fair Value (Level 3) [Member] \| Fair Value, Measurements, Recurring [Member] \| Corporate Bond Securities [Member]
Financial Assets:
AFS securities	0	0
Company Determined Fair Value (Level 3) [Member] \| Fair Value, Measurements, Recurring [Member] \| Equity Securities [Member]
Financial Assets:
AFS securities	0	0
Interest Rate Swap [Member] \| Fair Value, Measurements, Recurring [Member]
Financial Assets:
Customer interest rate swaps	17,756	7,841
Financial Liabilities:
Customer interest rate swaps	17,756	7,841
Interest Rate Swap [Member] \| Observable Market Data (Level 2) [Member] \| Fair Value, Measurements, Recurring [Member]
Financial Assets:
Customer interest rate swaps	17,756	7,841
Financial Liabilities:
Customer interest rate swaps	17,756	7,841
Interest Rate Lock Commitments [Member] \| Fair Value, Measurements, Recurring [Member]
Financial Assets:
Customer interest rate swaps	480	95
Financial Liabilities:
Customer interest rate swaps	18	28
Interest Rate Lock Commitments [Member] \| Observable Market Data (Level 2) [Member] \| Fair Value, Measurements, Recurring [Member]
Financial Assets:
Customer interest rate swaps	480	95
Financial Liabilities:
Customer interest rate swaps	18	28
Interest Rate Lock Commitments [Member] \| Company Determined Fair Value (Level 3) [Member] \| Fair Value, Measurements, Recurring [Member]
Financial Liabilities:
Customer interest rate swaps	0	0
Forward Contracts [Member] \| Fair Value, Measurements, Recurring [Member]
Financial Assets:
Customer interest rate swaps	312	32
Financial Liabilities:
Customer interest rate swaps	15	17
Forward Contracts [Member] \| Observable Market Data (Level 2) [Member] \| Fair Value, Measurements, Recurring [Member]
Financial Assets:
Customer interest rate swaps	312	32
Financial Liabilities:
Customer interest rate swaps	$ 15	17
Forward-Starting Interest Rate Swap [Member] \| Fair Value, Measurements, Recurring [Member]
Financial Liabilities:
Junior subordinated debt interest rate swaps		30
Forward-Starting Interest Rate Swap [Member] \| Observable Market Data (Level 2) [Member] \| Fair Value, Measurements, Recurring [Member]
Financial Liabilities:
Junior subordinated debt interest rate swaps		30
Other Assets [Member] \| Fair Value, Measurements, Recurring [Member]
Financial Assets:
Customer interest rate swaps		746
Other Assets [Member] \| Observable Market Data (Level 2) [Member] \| Fair Value, Measurements, Recurring [Member]
Financial Assets:
Customer interest rate swaps		$ 746

No definition available.

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

- Definition

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

+ References

No definition available.

+ Details

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

- Definition

Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=109250915&loc=d3e13433-108611

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226008-175313

+ Details

Name:	us-gaap_DerivativeLiabilities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Fair value as of the balance sheet date of all derivative assets not designated as hedging instruments.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4B
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5624163-113959

+ Details

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

- Definition

Fair value as of the balance sheet date of all derivative liabilities not designated as hedging instruments.

+ References

+ Details

Name:	us-gaap_InterestRateDerivativeInstrumentsNotDesignatedAsHedgingInstrumentsLiabilityAtFairValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- References

No definition available.

+ Details

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

- Definition

The face amount of loans that will be sold to other entities.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=82891408&loc=d3e4428-111522

+ Details

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

- Definition

Amount of investments classified as other.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.1(f,g))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.12)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_USStatesAndPoliticalSubdivisionsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=cac_CollateralizedMortgageObligationsIssuedByUnitedStatesGovernmentSponsoredEnterprisesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_CorporateBondSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_EquitySecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel1Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel2Member
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:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_InterestRateSwapMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_InterestRateLockCommitmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_ForwardContractsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=cac_ForwardStartingInterestRateSwapMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BalanceSheetLocationAxis=us-gaap_OtherAssetsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: