XML 50 R38.htm IDEA: XBRL DOCUMENT
v3.10.0.1

SECURITIES - Sales and Calls (Details) - USD ($) $ in Thousands | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2018 | Jun. 30, 2017 | Jun. 30, 2018 | Jun. 30, 2017
Investments, Debt and Equity Securities [Abstract] |  |  |  |
Proceeds | $ 0 | $ 540 | $ 0 | $ 540
Gross gains | 0 | 12 | 0 | 12
Tax expense | $ 0 | $ 4 | $ 0 | $ 4

X
- Definition Gains From Sale Of Available For Sale Securities Debt + References No definition available. + Details
Name: | chmg_GainsFromSaleOfAvailableForSaleSecuritiesDebt
Namespace Prefix: | chmg_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Proceeds from Sale and Maturity of Debt Securities, Available-for-sale + References No definition available. + Details
Name: | chmg_ProceedsfromSaleandMaturityofDebtSecuritiesAvailableforsale
Namespace Prefix: | chmg_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition This item represents the tax expense on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities. + References No definition available. + Details
Name: | chmg_TaxExpenseFromSaleOfAvailableForSaleSecuritiesDebt
Namespace Prefix: | chmg_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- References No definition available. + Details
Name: | us-gaap_InvestmentsDebtAndEquitySecuritiesAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration