ACCUMULATED OTHER COMPREHENSIVE INCOME - Reclassifications (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net securities gains	$ 0	$ 314	$ 797	$ 363
Income tax expense	5,469	5,377	16,204	13,468
Net income	24,119	22,776	71,450	59,745
Other expense	2,694	2,175	6,842	6,255
Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net income	(46)	200	494	145
Reclassification out of Accumulated Other Comprehensive Income | Unrealized Gains and Losses on Available- for-Sales Securities
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net securities gains	0	314	797	363
Income tax expense	0	(66)	(167)	(76)
Net income	0	248	630	287
Reclassification out of Accumulated Other Comprehensive Income | Defined Benefit Pension Items
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income tax expense	15	15	45	47
Net income	(46)	(48)	(136)	(142)
Other expense	$ (61)	$ (63)	$ (181)	$ (189)