Shareholders' Equity (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Oct. 08, 2015
Total risk-based capital:
Actual Regulatory Capital - Amount	$ 455,702	$ 434,331
Capital To Risk Weighted Assets	0.00%	0.00%
Minimum Requirement for capital Adequacy Including Capital Buffer Total Risk-Based Capital Ratio	10.50%
Minimum Regulatory Capital Required - Ratio		9.875%
Tier 1 capital:
Actual Regulatory Capital - Amount	$ 415,511	$ 394,597
Actual Regulatory Capital - Ratio	0.00%	0.00%
Minimum Requirement for capital Adequacy Including Capital Buffer Tier I Risk-Based Capital Ratio	8.50%
Minimum Regulatory Capital Required - Ratio		7.875%
Common equity tier I capital	$ 372,511	$ 351,597
Tier 1 leverage capital ratio:
Actual Regulatory Capital - Amount	$ 415,511	$ 394,597
Actual Regulatory Capital - Ratio	0.00%	0.00%
Minimum Regulatory Capital Required - Ratio	4.00%	4.00%
Common Equity Tier I Risk Based Capital Ratio	0.00%	0.00%
Minimum Requirement for capital Adequacy Including Capital Buffer Common Equity Tier I Risk-Based Capital Ratio	7.00%
Common Equity Tier One Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets		6.375%
Value Of Trust Preferred Securities Included In Tier 1 Capital	$ 43,000	$ 43,000	$ 43,000
Subordinated Debt	59,080	59,067	$ 15,000
Subsidiaries [Member]
Total risk-based capital:
Actual Regulatory Capital - Amount	$ 423,540	$ 398,773
Capital To Risk Weighted Assets	0.00%	0.00%
Minimum Requirement for capital Adequacy Including Capital Buffer Total Risk-Based Capital Ratio	10.50%
Minimum Regulatory Capital Required - Ratio		9.875%
Minimum Regulatory Provision To Be Well Capitalized - Ratio	10.00%	10.00%
Tier 1 capital:
Actual Regulatory Capital - Amount	$ 398,349	$ 374,039
Actual Regulatory Capital - Ratio	0.00%	0.00%
Minimum Requirement for capital Adequacy Including Capital Buffer Tier I Risk-Based Capital Ratio	8.50%
Minimum Regulatory Capital Required - Ratio		7.875%
Minimum Regulatory Provision To Be Well Capitalized - Ratio	8.00%	8.00%
Common equity tier I capital	$ 398,349	$ 374,039
Tier 1 leverage capital ratio:
Actual Regulatory Capital - Amount	$ 398,349	$ 374,039
Actual Regulatory Capital - Ratio	0.00%	0.00%
Minimum Regulatory Capital Required - Ratio	4.00%	4.00%
Minimum Regulatory Provision To Be Well Capitalized - Ratio	5.00%	5.00%
Common Equity Tier I Risk Based Capital Ratio	0.00%	0.00%
Minimum Requirement for capital Adequacy Including Capital Buffer Common Equity Tier I Risk-Based Capital Ratio	7.00%
Common Equity Tier One Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets		6.375%
Common Equity Tier One Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets	6.50%	6.50%
Tier II Capital [Domain]
Tier 1 leverage capital ratio:
Subordinated Debt	$ 15,000	$ 15,000

Common Equity Tier I To Total Risk Weighted Assets Capital Ratio

No definition available.

Name:	cac_CommonEquityTierIRiskBasedCapitalRatio
Namespace Prefix:	cac_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Common Equity Tier One Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets

+ References

No definition available.

+ Details

Name:	cac_CommonEquityTierOneRiskBasedCapitalRequiredforCapitalAdequacytoRiskWeightedAssets
Namespace Prefix:	cac_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Common Equity Tier One Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets

+ References

No definition available.

+ Details

Name:	cac_CommonEquityTierOneRiskBasedCapitalRequiredtobeWellCapitalizedtoRiskWeightedAssets
Namespace Prefix:	cac_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Common equity tier I capital

+ References

No definition available.

+ Details

Name:	cac_CommonequitytierIcapital
Namespace Prefix:	cac_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Minimum Requirement for capital Adequacy Including Capital Buffer Common Equity Tier I Risk-Based Capital Ratio

+ References

No definition available.

+ Details

Name:	cac_MinimumRequirementforcapitalAdequacyIncludingCapitalBufferCommonEquityTierIRiskBasedCapitalRatio
Namespace Prefix:	cac_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Minimum Requirement for capital Adequacy Including Capital Buffer Tier I Risk-Based Capital Ratio

+ References

No definition available.

+ Details

Name:	cac_MinimumRequirementforcapitalAdequacyIncludingCapitalBufferTierIRiskBasedCapitalRatio
Namespace Prefix:	cac_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Minimum Requirement for capital Adequacy Including Capital Buffer Total Risk-Based Capital Ratio

+ References

No definition available.

+ Details

Name:	cac_MinimumRequirementforcapitalAdequacyIncludingCapitalBufferTotalRiskBasedCapitalRatio
Namespace Prefix:	cac_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Value of trust preferred securities included in Tier I Capital.

+ References

No definition available.

+ Details

Name:	cac_ValueOfTrustPreferredSecuritiesIncludedInTierOneCapital
Namespace Prefix:	cac_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The amount of total capital as defined in the regulations.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 948
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=6490092&loc=d3e47304-110998

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1H
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=84167132&loc=d3e65071-112826

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 948
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=6490092&loc=d3e47080-110998

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1H
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=84167132&loc=d3e65071-112826

+ Details

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

- References

No definition available.

+ Details

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

- Definition

The minimum Total risk based capital ratio (total capital divided by risk weighted assets) required for capital adequacy purposes under the regulatory framework for prompt corrective action.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=84167132&loc=SL5958568-112826

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=84167132&loc=SL5958570-112826

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1H
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=84167132&loc=d3e65071-112826

+ Details

Name:	us-gaap_CapitalRequiredForCapitalAdequacyToRiskWeightedAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The Total risk based capital ratio (total capital divided by risk weighted assets) required to be categorized as "well capitalized", in the regulatory framework for prompt corrective action.

+ References

+ Details

Name:	us-gaap_CapitalRequiredToBeWellCapitalizedToRiskWeightedAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Total Capital divided by risk weighted assets as defined in the regulations.

+ References

+ Details

Name:	us-gaap_CapitalToRiskWeightedAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The amount of excess Tier 1 Leverage Capital divided by average assets as defined in the regulations.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=84167132&loc=SL5958568-112826

+ Details

Name:	us-gaap_ExcessTierOneLeverageCapitalToAverageAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Including the current and noncurrent portions, carrying value as of the balance sheet date of subordinated debt (with initial maturities beyond one year or beyond the operating cycle if longer). Subordinated debt places a lender in a lien position behind debt having a higher priority of repayment in liquidation of the entity's assets.

+ References

Reference 1: 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(19))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 3: 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(a)(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 4: 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(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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

- Definition

Tier 1 Leverage Capital as defined in the regulations. Also called Core Capital.

+ References

+ Details

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

- References

No definition available.

+ Details

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

- Definition

The minimum amount of Tier 1 Leverage Capital for capital adequacy purposes divided by average assets as defined in the regulations.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1H
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=84167132&loc=d3e65071-112826

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=84167132&loc=SL5958570-112826

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=84167132&loc=SL5958568-112826

+ Details

Name:	us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacyToAverageAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The amount of Tier 1 Leverage Capital required to be categorized as well capitalized divided by average assets as defined in the regulatory framework for prompt corrective action.

+ References

+ Details

Name:	us-gaap_TierOneLeverageCapitalRequiredToBeWellCapitalizedToAverageAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Tier 1 Risk Based Capital as defined in the regulations.

+ References

+ Details

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

- References

No definition available.

+ Details

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

- Definition

The minimum Tier One Capital Ratio (Tier one capital divided by risk-weighted assets) required for capital adequacy purposes under the regulatory framework for prompt corrective action.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=84167132&loc=SL5958570-112826

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=84167132&loc=SL5958568-112826

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1H
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=84167132&loc=d3e65071-112826

+ Details

Name:	us-gaap_TierOneRiskBasedCapitalRequiredForCapitalAdequacyToRiskWeightedAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The Tier 1 capital ratio (Tier 1 capital divided by risk weighted assets) required to be categorized as "well capitalized" under the regulatory framework for prompt corrective action.

+ References

+ Details

Name:	us-gaap_TierOneRiskBasedCapitalRequiredToBeWellCapitalizedToRiskWeightedAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Tier 1 capital divided by risk weighted assets as defined by regulations.

+ References

+ Details

Name:	us-gaap_TierOneRiskBasedCapitalToRiskWeightedAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	srt_ConsolidatedEntitiesAxis=srt_SubsidiariesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=cac_TierIICapitalDomain
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: