ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) - Changes in Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance	$ 598,100	$ 521,704
Net current period other comprehensive income	10,491	8,678
Balance	606,572	543,267
Accumulated Other Comprehensive Income (Loss)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance	12,059	(6,191)
Other comprehensive income before reclassification	10,444	8,663
Amounts reclassified from accumulated other comprehensive income	47	15
Net current period other comprehensive income	10,491	8,678
Balance	22,550	2,487
AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-sale, Parent [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance	13,607	(4,796)
Other comprehensive income before reclassification	10,444	8,663
Amounts reclassified from accumulated other comprehensive income	0	(23)
Net current period other comprehensive income	10,444	8,640
Balance	24,051	3,844
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance	(1,548)	(1,395)
Other comprehensive income before reclassification	0	0
Amounts reclassified from accumulated other comprehensive income	47	38
Net current period other comprehensive income	47	38
Balance	$ (1,501)	$ (1,357)