PENSION PLAN AND OTHER BENEFIT PLANS - Additional Information (Details) - USD ($) $ in Thousands			12 Months Ended
	Jan. 01, 2018	Oct. 20, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Hours requirement to be eligible		1000 hours
Defined Contribution Profit Sharing, Savings and Investment Plan
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, employer non-discretionary contribution amount			3.00%
Defined contribution plan, employer matching contribution, percent of employees' gross pay			6.00%
Total expense			$ 1,217	$ 1,160	$ 609
Chemung common stock included in defined contribution plan assets (in shares)			148,716	155,336	174,957
Defined Contribution Supplemental Executive Retirement Plan
Defined Benefit Plan Disclosure [Line Items]
Total expense			$ 341	$ 279	$ 262
Balance in the plan			1,214	872
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Lump sum settlement payments to employee			3,288	0
Settlement charge			(828)	$ 0	$ 0
Other comprehensive income, defined benefit plans, increase (decrease) in net unamortized gain loss arising during period net of tax			$ 300
Total unrecognized net loss increased percentage of obligation amortization threshold			10.00%
Total unrecognized net loss increased(decreased) percentage of plan assets threshold			10.00%
Average total life expectancy of participants	26 years 4 months 16 days
Other Postretirement Benefit Plan
Defined Benefit Plan Disclosure [Line Items]
Other comprehensive income, defined benefit plans, increase (decrease) in net unamortized gain loss arising during period net of tax			$ 101
Average future working lifetime of active participants			5 years
Executive Supplemental Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Total unrecognized net loss increased percentage of obligation amortization threshold			10.00%
Total unrecognized net loss increased(decreased) percentage of plan assets threshold			10.00%
Average total life expectancy of participants	13 years 4 months 25 days
Defined benefit plan, increase(decrease) in total unrecognized net loss			$ 54