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FEDERAL HOME LOAN BANK TERM ADVANCES AND OVERNIGHT ADVANCES (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Summary of Federal Home Loan Bank fixed rate advances [Abstract]
Amount	$ 50,140,000us-gaap_FederalHomeLoanBankAdvancesLongTerm
Rate (in hundredths)	1.73%us-gaap_FederalHomeLoanBankAdvancesBranchOfFHLBBankInterestRate	3.93%us-gaap_FederalHomeLoanBankAdvancesBranchOfFHLBBankInterestRate
Collateral pledged for Federal Home Loan Bank advances	152,700,000us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresCollateralPledged1	145,100,000us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresCollateralPledged1
Maximum amount eligible to borrow	86,000,000us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresMaximumAmountAvailable
Federal Home Loan Bank Advances Maturing December 22, 2016 [Member]
Summary of Federal Home Loan Bank fixed rate advances [Abstract]
Amount	10,000,000us-gaap_FederalHomeLoanBankAdvancesLongTerm / chmg_FederalHomeLoanBankAdvancesMaturityPeriodsAxis = chmg_FederalHomeLoanBankAdvancesMaturingDecember222016Member	10,000,000us-gaap_FederalHomeLoanBankAdvancesLongTerm / chmg_FederalHomeLoanBankAdvancesMaturityPeriodsAxis = chmg_FederalHomeLoanBankAdvancesMaturingDecember222016Member
Rate (in hundredths)	4.60%us-gaap_FederalHomeLoanBankAdvancesBranchOfFHLBBankInterestRate / chmg_FederalHomeLoanBankAdvancesMaturityPeriodsAxis = chmg_FederalHomeLoanBankAdvancesMaturingDecember222016Member	4.60%us-gaap_FederalHomeLoanBankAdvancesBranchOfFHLBBankInterestRate / chmg_FederalHomeLoanBankAdvancesMaturityPeriodsAxis = chmg_FederalHomeLoanBankAdvancesMaturingDecember222016Member
Maturity Date	Dec. 22, 2016	Dec. 22, 2016
Federal Home Loan Bank Advances Maturing October 20, 2014 [Member]
Summary of Federal Home Loan Bank fixed rate advances [Abstract]
Amount		4,134,000us-gaap_FederalHomeLoanBankAdvancesLongTerm / chmg_FederalHomeLoanBankAdvancesMaturityPeriodsAxis = chmg_FederalHomeLoanBankAdvancesMaturingOctober202014Member
Rate (in hundredths)		3.84%us-gaap_FederalHomeLoanBankAdvancesBranchOfFHLBBankInterestRate / chmg_FederalHomeLoanBankAdvancesMaturityPeriodsAxis = chmg_FederalHomeLoanBankAdvancesMaturingOctober202014Member
Maturity Date		Oct. 20, 2014
Federal Home Loan Bank Advances Maturing October 19, 2017 [Member]
Summary of Federal Home Loan Bank fixed rate advances [Abstract]
Amount	4,138,000us-gaap_FederalHomeLoanBankAdvancesLongTerm / chmg_FederalHomeLoanBankAdvancesMaturityPeriodsAxis = chmg_FederalHomeLoanBankAdvancesMaturingOctober192017Member	4,134,000us-gaap_FederalHomeLoanBankAdvancesLongTerm / chmg_FederalHomeLoanBankAdvancesMaturityPeriodsAxis = chmg_FederalHomeLoanBankAdvancesMaturingOctober192017Member
Rate (in hundredths)	3.90%us-gaap_FederalHomeLoanBankAdvancesBranchOfFHLBBankInterestRate / chmg_FederalHomeLoanBankAdvancesMaturityPeriodsAxis = chmg_FederalHomeLoanBankAdvancesMaturingOctober192017Member	3.90%us-gaap_FederalHomeLoanBankAdvancesBranchOfFHLBBankInterestRate / chmg_FederalHomeLoanBankAdvancesMaturityPeriodsAxis = chmg_FederalHomeLoanBankAdvancesMaturingOctober192017Member
Maturity Date	Oct. 19, 2017	Oct. 19, 2017
Federal Home Loan Bank Advances Maturing December 4, 2017 [Member]
Summary of Federal Home Loan Bank fixed rate advances [Abstract]
Amount	3,103,000us-gaap_FederalHomeLoanBankAdvancesLongTerm / chmg_FederalHomeLoanBankAdvancesMaturityPeriodsAxis = chmg_FederalHomeLoanBankAdvancesMaturingDecember42017Member	3,100,000us-gaap_FederalHomeLoanBankAdvancesLongTerm / chmg_FederalHomeLoanBankAdvancesMaturityPeriodsAxis = chmg_FederalHomeLoanBankAdvancesMaturingDecember42017Member
Rate (in hundredths)	2.91%us-gaap_FederalHomeLoanBankAdvancesBranchOfFHLBBankInterestRate / chmg_FederalHomeLoanBankAdvancesMaturityPeriodsAxis = chmg_FederalHomeLoanBankAdvancesMaturingDecember42017Member	2.91%us-gaap_FederalHomeLoanBankAdvancesBranchOfFHLBBankInterestRate / chmg_FederalHomeLoanBankAdvancesMaturityPeriodsAxis = chmg_FederalHomeLoanBankAdvancesMaturingDecember42017Member
Maturity Date	Dec. 04, 2017	Dec. 04, 2017
Federal Home Loan Bank Advances Maturing January 2, 2018 [Member]
Summary of Federal Home Loan Bank fixed rate advances [Abstract]
Amount	2,069,000us-gaap_FederalHomeLoanBankAdvancesLongTerm / chmg_FederalHomeLoanBankAdvancesMaturityPeriodsAxis = chmg_FederalHomeLoanBankAdvancesMaturingJanuary22018Member	2,067,000us-gaap_FederalHomeLoanBankAdvancesLongTerm / chmg_FederalHomeLoanBankAdvancesMaturityPeriodsAxis = chmg_FederalHomeLoanBankAdvancesMaturingJanuary22018Member
Rate (in hundredths)	3.05%us-gaap_FederalHomeLoanBankAdvancesBranchOfFHLBBankInterestRate / chmg_FederalHomeLoanBankAdvancesMaturityPeriodsAxis = chmg_FederalHomeLoanBankAdvancesMaturingJanuary22018Member	3.05%us-gaap_FederalHomeLoanBankAdvancesBranchOfFHLBBankInterestRate / chmg_FederalHomeLoanBankAdvancesMaturityPeriodsAxis = chmg_FederalHomeLoanBankAdvancesMaturingJanuary22018Member
Maturity Date	Jan. 02, 2018	Jan. 02, 2018
Federal Home Loan Bank Advances Maturing January 2, 2015 [Member]
Summary of Federal Home Loan Bank fixed rate advances [Abstract]
Amount	30,830,000us-gaap_FederalHomeLoanBankAdvancesLongTerm / chmg_FederalHomeLoanBankAdvancesMaturityPeriodsAxis = chmg_FederalHomeLoanBankAdvancesMaturingJanuary22015Member
Rate (in hundredths)	0.32%us-gaap_FederalHomeLoanBankAdvancesBranchOfFHLBBankInterestRate / chmg_FederalHomeLoanBankAdvancesMaturityPeriodsAxis = chmg_FederalHomeLoanBankAdvancesMaturingJanuary22015Member
Maturity Date	Jan. 02, 2015
Federal Home Loan Bank Advances Maturing June 18, 2014 [Member]
Summary of Federal Home Loan Bank fixed rate advances [Abstract]
Amount		1,033,000us-gaap_FederalHomeLoanBankAdvancesLongTerm / chmg_FederalHomeLoanBankAdvancesMaturityPeriodsAxis = chmg_FederalHomeLoanBankAdvancesMaturingJune182014Member
Rate (in hundredths)		3.20%us-gaap_FederalHomeLoanBankAdvancesBranchOfFHLBBankInterestRate / chmg_FederalHomeLoanBankAdvancesMaturityPeriodsAxis = chmg_FederalHomeLoanBankAdvancesMaturingJune182014Member
Maturity Date		Jun. 18, 2014
Federal Home Loan Bank Advances Maturing October 2, 2014 [Member]
Summary of Federal Home Loan Bank fixed rate advances [Abstract]
Amount		$ 775,000us-gaap_FederalHomeLoanBankAdvancesLongTerm / chmg_FederalHomeLoanBankAdvancesMaturityPeriodsAxis = chmg_FederalHomeLoanBankAdvancesMaturingOctober22014Member
Rate (in hundredths)		3.05%us-gaap_FederalHomeLoanBankAdvancesBranchOfFHLBBankInterestRate / chmg_FederalHomeLoanBankAdvancesMaturityPeriodsAxis = chmg_FederalHomeLoanBankAdvancesMaturingOctober22014Member
Maturity Date		Oct. 02, 2014
Federal Home Loan Bank Advances Maturing January 19, 2014 [Member]
Summary of Federal Home Loan Bank fixed rate advances [Abstract]
Call Date		Jan. 19, 2014
Federal Home Loan Bank Advances Maturing January 19, 2015 [Member]
Summary of Federal Home Loan Bank fixed rate advances [Abstract]
Call Date	Jan. 19, 2015
Federal Home Loan Bank Advances Maturing January 20, 2014 [Member]
Summary of Federal Home Loan Bank fixed rate advances [Abstract]
Call Date		Jan. 20, 2014
Federal Home Loan Bank Advances Maturing March 4, 2014 [Member]
Summary of Federal Home Loan Bank fixed rate advances [Abstract]
Call Date		Mar. 04, 2014
Federal Home Loan Bank Advances Maturing April 1, 2014 [Member]
Summary of Federal Home Loan Bank fixed rate advances [Abstract]
Call Date		Apr. 01, 2014
Federal Home Loan Bank Advances Maturing April 1, 2015 [Member]
Summary of Federal Home Loan Bank fixed rate advances [Abstract]
Call Date	Apr. 01, 2015
Federal Home Loan Bank Advances Maturing March 3, 2015 [Member]
Summary of Federal Home Loan Bank fixed rate advances [Abstract]
Call Date	Mar. 03, 2015

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Discloses the earliest year of maturity for the advances from the Federal Home Loan Bank, by branch, as of the Balance Sheet date.

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Date when the advance is scheduled to be fully repaid, in CCYY-MM-DD format.

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Discloses the single interest rate [if] applicable to the advances from the Federal Home Loan Bank, by branch, as of the Balance Sheet date.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

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Amount of the collateral pledged in support of federal home loan bank advances outstanding.

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Amount of maximum advances or credit lines available from the Federal Home Loan Bank (FHLB).

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Including both current and noncurrent portions, Federal Home Loan Bank borrowings initially due beyond one year or beyond the normal operating cycle if longer.

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