ACCUMULATED OTHER COMPREHENSIVE INCOME - Changes in Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	$ 609,102	$ 651,668	$ 704,906	$ 657,184
Net current period other comprehensive (loss) income	(64,847)	7,161	(174,627)	(5,473)
Ending balance	562,063	677,471	562,063	677,471
Total
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(93,687)	15,110	16,093	27,744
Other comprehensive income (loss) before reclassification	(65,179)	7,151	(174,986)	(4,933)
Amounts reclassified from accumulated other comprehensive income (loss)	332	10	359	(540)
Net current period other comprehensive (loss) income	(64,847)	7,161	(174,627)	(5,473)
Ending balance	(158,534)	22,271	(158,534)	22,271
Unrealized Gains and Losses on Available- for-Sales Securities
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(92,751)	16,503	17,056	29,182
Other comprehensive income (loss) before reclassification	(65,179)	7,151	(174,986)	(4,933)
Amounts reclassified from accumulated other comprehensive income (loss)	305	(35)	305	(630)
Net current period other comprehensive (loss) income	(64,874)	7,116	(174,681)	(5,563)
Ending balance	(157,625)	23,619	(157,625)	23,619
Defined Benefit Pension Items
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(936)	(1,393)	(963)	(1,438)
Other comprehensive income (loss) before reclassification	0	0	0	0
Amounts reclassified from accumulated other comprehensive income (loss)	27	45	54	90
Net current period other comprehensive (loss) income	27	45	54	90
Ending balance	$ (909)	$ (1,348)	$ (909)	$ (1,348)