Summary of Impaired Loan Balances and Associated Allowance by Portfolio Segment (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended	9 Months Ended	12 Months Ended
Sep. 30, 2012	Sep. 30, 2012	Dec. 31, 2011
Financing Receivable, Impaired [Line Items]
Recorded Investment	$ 6,408	$ 6,408	$ 5,532
Recorded Investment	19,027	19,027	21,854
Unpaid Principal Balance	9,003	9,003	7,655
Unpaid Principal Balance	19,027	19,027	22,424
Related Allowance
Average Recorded Investment	5,127	5,842	4,758
Interest Income Recognized	24	11	21
Recorded Investment	25,435	25,435	27,386
Unpaid Principal Balance	28,030	28,030	30,079
Related Allowance	3,094	3,094	3,671
Average Recorded Investment	27,396	26,809	28,821
Average Recorded Investment	22,269	20,967	24,063
Interest Income Recognized	112	42	141
Interest Income Recognized	88	31	120
Residential real estate loans
Financing Receivable, Impaired [Line Items]
Recorded Investment	3,321	3,321	1,998
Recorded Investment	9,233	9,233	10,717
Unpaid Principal Balance	4,324	4,324	1,810
Unpaid Principal Balance	9,233	9,233	11,287
Related Allowance
Average Recorded Investment	2,324	2,923	1,847
Interest Income Recognized	20	7	21
Related Allowance	2,071	2,071	1,364
Average Recorded Investment	10,803	10,106	11,280
Interest Income Recognized	88	31	109
Commercial real estate loans
Financing Receivable, Impaired [Line Items]
Recorded Investment	2,096	2,096	2,353
Recorded Investment	5,025	5,025	5,477
Unpaid Principal Balance	2,341	2,341	3,815
Unpaid Principal Balance	5,025	5,025	5,478
Related Allowance
Average Recorded Investment	1,723	1,860	2,078
Related Allowance	343	343	961
Average Recorded Investment	5,839	5,679	7,257
Interest Income Recognized			3
Commercial loans
Financing Receivable, Impaired [Line Items]
Recorded Investment	394	394	383
Recorded Investment	3,435	3,435	3,636
Unpaid Principal Balance	710	710	665
Unpaid Principal Balance	3,435	3,435	3,636
Related Allowance
Average Recorded Investment	347	462	393
Interest Income Recognized	4	4
Related Allowance	376	376	815
Average Recorded Investment	4,062	3,862	3,963
Interest Income Recognized			7
Home equity loans
Financing Receivable, Impaired [Line Items]
Recorded Investment	591	591	782
Recorded Investment	1,077	1,077	1,888
Unpaid Principal Balance	1,462	1,462	1,189
Unpaid Principal Balance	1,077	1,077	1,887
Related Allowance
Average Recorded Investment	726	591	422
Related Allowance	265	265	440
Average Recorded Investment	1,331	1,063	1,457
Interest Income Recognized			1
Consumer loans
Financing Receivable, Impaired [Line Items]
Recorded Investment	6	6	16
Recorded Investment	257	257	136
Unpaid Principal Balance	166	166	176
Unpaid Principal Balance	257	257	136
Related Allowance
Average Recorded Investment	7	6	18
Related Allowance	39	39	91
Average Recorded Investment	$ 234	$ 257	$ 106

Impaired Financing Receivable, With No Related Allowance, Related Allowance

No definition available.

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

- Details

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

- Definition

Average amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 15

-Subparagraph (c)(1)

-URI http://asc.fasb.org/extlink&oid=7512638&loc=d3e5212-111524

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 17

-URI http://asc.fasb.org/extlink&oid=7512638&loc=d3e5258-111524

+ Details

Name:	us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of interest income recognized that the financing receivables (with related allowance for credit losses and without a related allowance for credit losses) were impaired.

+ References

+ Details

Name:	us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 14A

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=7512638&loc=SL6953550-111524

+ Details

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

- Definition

Amount of allowance for credit losses related to recorded investment.

+ References

+ Details

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

- Definition

Amount of unpaid principal balance of impaired financing receivables with related allowance for credit losses and without related allowance for credit losses.

+ References

+ Details

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

- Definition

Amount of average investment of impaired financing receivables for which there is no related allowance for credit losses.

+ References

+ Details

Name:	us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of interest income, recognized on accrual basis, on financing receivables that are recognized as impaired, for which there is no related allowance for credit losses.

+ References

+ Details

Name:	us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceInterestIncomeAccrualMethod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of investment in impaired financing receivables for which there is no related allowance for credit losses.

+ References

+ Details

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

- Definition

Amount of unpaid principal balance of impaired financing receivables for which there is no related allowance for credit losses.

+ References

+ Details

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

- Definition

Amount of average investment of impaired financing receivables for which there is a related allowance for credit losses.

+ References

+ Details

Name:	us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of interest income, recognized on accrual basis, on financing receivables, for which there is a related allowance for credit losses and are recognized as impaired.

+ References

+ Details

Name:	us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceInterestIncomeAccrualMethod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of investment in impaired financing receivables for which there is a related allowance for credit losses.

+ References

+ Details

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

- Definition

Unpaid principal balance of impaired financing receivables for which there is a related allowance for credit losses.

+ References

+ Details

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