SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Jan. 01, 2018
Property, Plant and Equipment [Line Items]
Adjusted cumulative effect of accounting change			$ (162)
Period of delinquency after which a loan is placed on non-accrual status	90 days
Number of consecutive months for which loans remain current before non-accrual loans are returned to accrual status	6 months
Rolling historical period of net losses used in evaluating general component of valuation allowance for loans not impaired but classified as substandard and special mention	5 years
Number of most recent years of actual loss history used in determining historical loss experience for all other unclassified loans	2 years
Assets under management	$ 1,915,000	$ 1,768,000
Buildings | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful lives	15 years
Buildings | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful lives	50 years
Equipment and Furniture | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful lives	3 years
Equipment and Furniture | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful lives	10 years
Chemung Financial Corporation
Property, Plant and Equipment [Line Items]
Assets under management	$ 290,000	$ 283,000
Retained Earnings
Property, Plant and Equipment [Line Items]
Adjusted cumulative effect of accounting change			40
Accumulated Other Comprehensive Income (Loss)
Property, Plant and Equipment [Line Items]
Adjusted cumulative effect of accounting change			(202)
Accounting Standards Update 2016-01 | Retained Earnings
Property, Plant and Equipment [Line Items]
Adjusted cumulative effect of accounting change			40
Accounting Standards Update 2016-01 | Accumulated Other Comprehensive Income (Loss)
Property, Plant and Equipment [Line Items]
Adjusted cumulative effect of accounting change			$ (202)