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CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY (UNAUDITED) (Parenthetical) (USD $) | 3 Months Ended
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Mar. 31, 2015 | Mar. 31, 2014
Increase (Decrease) in Shareholders' Equity [Roll Forward] |  |
Cash dividends declared (in dollars per share) | $ 0.26 us-gaap_CommonStockDividendsPerShareDeclared | $ 0.26 us-gaap_CommonStockDividendsPerShareDeclared
Distribution of shares of treasury stock for directors' compensation (in shares) | 9,673 chmg_DistributionOfSharesOfTreasuryStockForDirectorsCompensationShares | 8,385 chmg_DistributionOfSharesOfTreasuryStockForDirectorsCompensationShares
Distribution of shares of treasury stock granted for employee restricted stock awards (in shares) |  | 990 chmg_DistributionOfTreasuryStockForEmployeeRestrictedStockAwardsShares
Distribution of shares of treasury stock for employee compensation (in shares) | 3,303 us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation | 3,595 us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation
Sale of shares of treasury stock (in shares) | 5,728 us-gaap_StockIssuedDuringPeriodSharesTreasuryStockReissued |

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- Definition Number of treasury shares issued during the period for directors' compensation. + References No definition available. + Details
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- Definition Number of shares of treasury stock issued during the period for employee restricted stock awards. + References No definition available. + Details
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- Definition Aggregate dividends declared during the period for each share of common stock outstanding. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Article 3 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.3-04) -URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770 + Details
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- Definition Number of shares (or other type of equity) issued during the period as a result of any equity-based compensation plan other than an employee stock ownership plan (ESOP), net of any shares forfeited. Shares issued could result from the issuance of restricted stock, the exercise of stock options, stock issued under employee stock purchase plans, and/or other employee benefit plans. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Article 3 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21463-112644 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.3-04) -URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 29, 30 -Article 5 + Details
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- Definition Number of treasury shares (units) reissued during the period, excluding reissuance of shares (units) held in treasury used to satisfy equity-based compensation obligations exercised by the holders of such rights. Upon reissuance of shares (units) from treasury, either the common or preferred stock (unit) reissued is outstanding. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Article 3 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21463-112644 + Details
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