PARENT COMPANY FINANCIAL INFORMATION (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Assets:
Cash on deposit with subsidiary bank	$ 29,467	$ 25,203
Securities available for sale, at estimated fair value	554,611	284,090
Total assets	2,279,451	1,787,827	$ 1,755,343
Liabilities and shareholders' equity:
Dividends payable	1,214	1,263	1,254
Total liabilities	2,079,752	1,605,200
Shareholders' equity:
Total shareholders' equity	199,699	182,627	165,029	$ 149,813
Total liabilities and shareholders' equity	2,279,451	1,787,827
STATEMENTS OF INCOME [Abstract]
Income before income tax expense	23,869	19,043	23,635
Income tax benefit	4,607	3,434	4,009
Net of tax	19,262	15,609	19,626
Cash flows from operating activities:
Net income	19,262	15,609	19,626
Adjustments to reconcile net income to net cash provided by operating activities:
Change in other assets	(9,883)	(1,945)	(2,651)
Change in other liabilities	8,265	3,333	(654)
Net cash provided by operating activities	28,659	26,405	27,772
Cash flow from financing activities:
Cash dividends paid	(5,006)	(5,029)	(4,969)
Purchase of treasury stock	(7,589)	0	0
Sale of treasury stock	1,018	585	643
Net cash (used in) provided by financing activities	453,823	(1,762)	27,552
Cash and cash equivalents, beginning of period	121,904
Cash and cash equivalents, end of period	108,538	121,904
Parent Company
Assets:
Cash on deposit with subsidiary bank	2,243	3,938
Dividends receivable from subsidiary bank	1,214	0
Securities available for sale, at estimated fair value	377	492
Other assets	1,420	1,266
Total assets	201,057	183,988
Liabilities and shareholders' equity:
Dividends payable	1,214	1,263
Other liabilities	144	98
Total liabilities	1,358	1,361
Shareholders' equity:
Total shareholders' equity	199,699	182,627
Total liabilities and shareholders' equity	201,057	183,988
STATEMENTS OF INCOME [Abstract]
Dividends from subsidiary bank and non-bank	10,806	4,516	3,187
Interest and dividend income	5	9	10
Non-interest income	(50)	(62)	(20)
Non-interest expenses	503	439	477
Income before impact of subsidiaries' undistributed earnings	10,258	4,024	2,700
Income before income tax expense	19,080	15,445	19,462
Income tax benefit	(182)	(164)	(164)
Net of tax	19,262	15,609	19,626
Cash flows from operating activities:
Net income	19,262	15,609	19,626
Adjustments to reconcile net income to net cash provided by operating activities:
Change in dividend receivable	(1,214)	0	1,233
Change in other assets	(154)	(196)	(32)
Change in other liabilities	6	(48)	773
Expense related to employee stock compensation	101	100	89
Expense related to restricted stock units for directors' deferred compensation plan	29	42	67
Expense to employee restricted stock awards	672	503	405
Net cash provided by operating activities	9,880	4,589	5,399
Cash flow from financing activities:
Cash dividends paid	(5,006)	(5,029)	(4,969)
Purchase of treasury stock	(7,589)	(185)	(112)
Sale of treasury stock	1,018	585	643
Net cash (used in) provided by financing activities	(11,577)	(4,629)	(4,438)
Net increase (decrease) in cash and cash equivalents	(1,697)	(40)	961
Cash and cash equivalents, beginning of period	3,938	3,978	3,017
Cash and cash equivalents, end of period	2,241	3,938	3,978
Parent Company | Chemung Canal Trust Company
Assets:
Investment in subsidiary	192,364	175,470
STATEMENTS OF INCOME [Abstract]
Income (loss) from equity method investments	8,204	11,220	16,670
Adjustments to reconcile net income to net cash provided by operating activities:
Equity in undistributed earnings	(8,204)	(11,220)	(16,670)
Parent Company | CFS Group Inc.
Assets:
Investment in subsidiary	876	868
STATEMENTS OF INCOME [Abstract]
Income (loss) from equity method investments	8	(4)	(32)
Adjustments to reconcile net income to net cash provided by operating activities:
Equity in undistributed earnings	(8)	4	32
Parent Company | Chemung Risk Management
Assets:
Investment in subsidiary	2,563	1,954
STATEMENTS OF INCOME [Abstract]
Income (loss) from equity method investments	610	205	124
Adjustments to reconcile net income to net cash provided by operating activities:
Equity in undistributed earnings	$ (610)	$ (205)	$ (124)