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FEDERAL HOME LOAN BANK TERM ADVANCES AND OVERNIGHT ADVANCES (Details) (USD $) | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013
Summary of Federal Home Loan Bank fixed rate advances [Abstract] |  |
Amount | $ 50,140,000 us-gaap_FederalHomeLoanBankAdvancesLongTerm |
Rate (in hundredths) | 1.73%us-gaap_FederalHomeLoanBankAdvancesBranchOfFHLBBankInterestRate | 3.93%us-gaap_FederalHomeLoanBankAdvancesBranchOfFHLBBankInterestRate
Collateral pledged for Federal Home Loan Bank advances | 152,700,000 us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresCollateralPledged1 | 145,100,000 us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresCollateralPledged1
Maximum amount eligible to borrow | 86,000,000 us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresMaximumAmountAvailable |
Federal Home Loan Bank Advances Maturing December 22, 2016 [Member] |  |
Summary of Federal Home Loan Bank fixed rate advances [Abstract] |  |
Amount | 10,000,000 us-gaap_FederalHomeLoanBankAdvancesLongTerm / chmg_FederalHomeLoanBankAdvancesMaturityPeriodsAxis = chmg_FederalHomeLoanBankAdvancesMaturingDecember222016Member | 10,000,000 us-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 |  | 4,134,000 us-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 | 4,138,000 us-gaap_FederalHomeLoanBankAdvancesLongTerm / chmg_FederalHomeLoanBankAdvancesMaturityPeriodsAxis = chmg_FederalHomeLoanBankAdvancesMaturingOctober192017Member | 4,134,000 us-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 | 3,103,000 us-gaap_FederalHomeLoanBankAdvancesLongTerm / chmg_FederalHomeLoanBankAdvancesMaturityPeriodsAxis = chmg_FederalHomeLoanBankAdvancesMaturingDecember42017Member | 3,100,000 us-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 | 2,069,000 us-gaap_FederalHomeLoanBankAdvancesLongTerm / chmg_FederalHomeLoanBankAdvancesMaturityPeriodsAxis = chmg_FederalHomeLoanBankAdvancesMaturingJanuary22018Member | 2,067,000 us-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 | 30,830,000 us-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 |  | 1,033,000 us-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 |  | $ 775,000 us-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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- Definition Discloses the earliest year of maturity for the advances from the Federal Home Loan Bank, by branch, as of the Balance Sheet date. + References No definition available. + Details
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- Definition Date when the advance is scheduled to be fully repaid, in CCYY-MM-DD format. + References No definition available. + Details
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- Definition 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 -Topic 942 -SubTopic 470 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6479118&loc=d3e64650-112822 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 470 -Section 50 -Paragraph 3 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6479336&loc=d3e64711-112823 + Details
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- Definition Amount of the collateral pledged in support of federal home loan bank advances outstanding. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 470 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6479118&loc=d3e64650-112822 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 470 -Section 50 -Paragraph 3 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=6479336&loc=d3e64711-112823 + Details
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- Definition Amount of maximum advances or credit lines available from the Federal Home Loan Bank (FHLB). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 470 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6479118&loc=d3e64650-112822 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 22 -Subparagraph b -Article 5 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.13(3)(a)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22 (b)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 13 -Subparagraph 3(a) -Article 9 + Details
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- Definition Including both current and noncurrent portions, Federal Home Loan Bank borrowings initially due beyond one year or beyond the normal operating cycle if longer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 470 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6479118&loc=d3e64650-112822 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.16) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 16 -Article 9 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 470 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6479336&loc=d3e64702-112823 + Details
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