Fair Value (Summary of Financial Assets and Liabilities Measured at Fair Value on Recurring Basis) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Financial Assets:
AFS securities	$ 763,063us-gaap_AvailableForSaleSecurities	$ 808,477us-gaap_AvailableForSaleSecurities
Trading account assets	2,457us-gaap_TradingSecurities	2,488us-gaap_TradingSecurities
Customer interest rate swap agreement		114
Financial Liabilities:
Interest rate swap agreements		3,912us-gaap_DerivativeLiabilities
Customer interest rate swap agreement		114
Obligations of states and political subdivisions [Member]
Financial Assets:
AFS securities	26,777	31,207
Mortgage-backed securities issued or guaranteed by U.S. government sponsored enterprises [Member]
Financial Assets:
AFS securities	381,308	395,903
Collateralized mortgage obligations issued or guaranteed by U.S. government sponsored enterprises [Member]
Financial Assets:
AFS securities	343,897	374,435
Private issue collateralized mortgage obligations [Member]
Financial Assets:
AFS securities	6,054	6,932
Fair Value, Measurements, Recurring [Member]
Financial Assets:
Trading account assets	2,457	2,488
Customer interest rate swap agreement	1,140	114
Financial Liabilities:
Interest rate swap agreements	9,143	3,912
Customer interest rate swap agreement	1,140	114
Fair Value, Measurements, Recurring [Member] \| Obligations of U.S. government sponsored enterprises [Member]
Financial Assets:
AFS securities	5,027
Fair Value, Measurements, Recurring [Member] \| Obligations of states and political subdivisions [Member]
Financial Assets:
AFS securities	26,777	31,207
Fair Value, Measurements, Recurring [Member] \| Mortgage-backed securities issued or guaranteed by U.S. government sponsored enterprises [Member]
Financial Assets:
AFS securities	381,308	395,903
Fair Value, Measurements, Recurring [Member] \| Collateralized mortgage obligations issued or guaranteed by U.S. government sponsored enterprises [Member]
Financial Assets:
AFS securities	343,897	374,435
Fair Value, Measurements, Recurring [Member] \| Private issue collateralized mortgage obligations [Member]
Financial Assets:
AFS securities	6,054	6,932
Readily Available Market Prices (Level 1) [Member]
Financial Assets:
Trading account assets	2,457	2,488
Readily Available Market Prices (Level 1) [Member] \| Fair Value, Measurements, Recurring [Member]
Financial Assets:
Trading account assets	2,457	2,488
Financial Liabilities:
Customer interest rate swap agreement	0	0
Observable Market Data (Level 2) [Member]
Financial Assets:
AFS securities	763,063	808,477
Customer interest rate swap agreement	1,140	114
Financial Liabilities:
Interest rate swap agreements	9,143	3,912
Customer interest rate swap agreement	1,140	114
Observable Market Data (Level 2) [Member] \| Fair Value, Measurements, Recurring [Member]
Financial Assets:
Customer interest rate swap agreement	1,140	114
Financial Liabilities:
Interest rate swap agreements	9,143	3,912
Customer interest rate swap agreement	1,140	114
Observable Market Data (Level 2) [Member] \| Fair Value, Measurements, Recurring [Member] \| Obligations of U.S. government sponsored enterprises [Member]
Financial Assets:
AFS securities	5,027
Observable Market Data (Level 2) [Member] \| Fair Value, Measurements, Recurring [Member] \| Obligations of states and political subdivisions [Member]
Financial Assets:
AFS securities	26,777	31,207
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	381,308	395,903
Observable Market Data (Level 2) [Member] \| Fair Value, Measurements, Recurring [Member] \| Collateralized mortgage obligations issued or guaranteed by U.S. government sponsored enterprises [Member]
Financial Assets:
AFS securities	343,897	374,435
Observable Market Data (Level 2) [Member] \| Fair Value, Measurements, Recurring [Member] \| Private issue collateralized mortgage obligations [Member]
Financial Assets:
AFS securities	6,054	6,932
Company Determined Fair Value (Level 3) [Member] \| Fair Value, Measurements, Recurring [Member]
Financial Liabilities:
Customer interest rate swap agreement	$ 0	$ 0

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

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 25

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=28360136&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 5

-Subparagraph (aa)

-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6871852&loc=d3e26610-111562

+ 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://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 10

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=35750535&loc=d3e13433-108611

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 45

-Paragraph 5

-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41228-113958

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 15

-URI http://asc.fasb.org/extlink&oid=35750535&loc=d3e13495-108611

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 20

-Section 50

-Paragraph 3

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=34720828&loc=SL20225862-175312

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 45

-Paragraph 6

-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41271-113958

Reference 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 20

-Section 55

-Paragraph 10

-URI http://asc.fasb.org/extlink&oid=36459792&loc=SL20226008-175313

+ Details

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

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4B

-Subparagraph (c)(2)

-URI http://asc.fasb.org/extlink&oid=35706170&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

- Details

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

- Definition

Amount of investments in debt and equity securities and other forms of securities that provide ownership interests classified as trading.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6871852&loc=d3e26610-111562

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6871852&loc=d3e26626-111562

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Trading Securities

-URI http://asc.fasb.org/extlink&oid=6526789

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.4)

-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

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

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

- Details

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

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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