ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Jun. 30, 2021	Dec. 31, 2020	Jun. 30, 2020	Dec. 31, 2019
Other Comprehensive Income (Loss), before Reclassification Adjustments and Tax [Abstract]
Unrealized gain (loss) on investment securities	$ (21,920)	$ 6,931	$ (46,262)	$ 35,474
Retirement obligation	0	0	0	0
Total	(21,920)	6,931	(46,262)	35,474
Other Comprehensive Income (Loss) Reclassifications before Tax [Abstract]
Realized gain (loss) on securities available-for-sale	(313)	2	(744)	(55)
Retirement obligation	(567)	(519)	(1,631)	(1,401)
Total	(880)	(517)	(2,375)	(1,456)
Transactions Pre-tax
Unrealized gain (loss) on investment securities	(21,607)	6,929	(45,518)	35,529
Unfunded pension obligation	567	519	1,631	1,401
Total	(21,040)	7,448	(43,887)	36,930
Transactions Tax-effect
Unrealized gain (loss) on investment securities	4,664	(1,495)	9,825	(7,668)
Retirement obligation	(129)	(118)	(372)	(319)
Total	4,535	(1,613)	9,453	(7,987)
Transactions Net of tax
Unrealized gain (loss) on investment securities	(16,943)	5,434	(35,693)	27,861
Retirement obligation	438	401	1,259	1,082
Total	(16,505)	5,835	(34,434)	28,943
Balances Net of tax
Unrealized gain (loss) on investment securities	37,883	69,125	37,883	69,125	$ 54,826	$ 73,576	$ 63,691	$ 41,264
Retirement obligation	(23,653)	(26,859)	(23,653)	(26,859)	(24,091)	(24,912)	(27,260)	(27,941)
Total	14,230	42,266	14,230	42,266	$ 30,735	$ 48,664	$ 36,431	$ 13,323
Accumulated other comprehensive income (loss)
Transactions Net of tax
Total	$ (16,505)	$ 5,835	$ (34,434)	$ 28,943