ACCUMULATED OTHER COMPREHENSIVE LOSS - Net Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	$ 1,536,865	$ 1,488,910	$ 1,483,768	$ 1,519,679
Other comprehensive loss before reclassification from accumulated other comprehensive loss, net of tax			5,347
Reclassifications from accumulated other comprehensive loss to earnings, net of tax			979
Total other comprehensive income/ (loss)	(9,634)	(28,182)	6,326	(88,914)
Balance at end of period	1,539,032	1,477,169	1,539,032	1,477,169
Total
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(115,991)	(69,271)	(131,951)	(8,539)
Other comprehensive loss before reclassification from accumulated other comprehensive loss, net of tax				(90,005)
Reclassifications from accumulated other comprehensive loss to earnings, net of tax				1,091
Total other comprehensive income/ (loss)	(9,634)	(28,182)	6,326	(88,914)
Balance at end of period	(125,625)	(97,453)	(125,625)	(97,453)
Unrealized Gains/(Losses) on Debt Securities Available-for-Sale
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period			(113,513)	(336)
Other comprehensive loss before reclassification from accumulated other comprehensive loss, net of tax			5,347	(77,922)
Reclassifications from accumulated other comprehensive loss to earnings, net of tax			0	(34)
Total other comprehensive income/ (loss)			5,347	(77,956)
Balance at end of period	(108,166)	(78,292)	(108,166)	(78,292)
Defined Benefit Pension Plan
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period			(8,002)	(8,203)
Other comprehensive loss before reclassification from accumulated other comprehensive loss, net of tax			0	0
Reclassifications from accumulated other comprehensive loss to earnings, net of tax			336	291
Total other comprehensive income/ (loss)			336	291
Balance at end of period	(7,666)	(7,912)	(7,666)	(7,912)
Unrealized Losses on Debt Securities Transferred from Available-for-Sale to Held-to-Maturity
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period			(10,436)	0
Other comprehensive loss before reclassification from accumulated other comprehensive loss, net of tax			0	(12,083)
Reclassifications from accumulated other comprehensive loss to earnings, net of tax			643	834
Total other comprehensive income/ (loss)			643	(11,249)
Balance at end of period	$ (9,793)	$ (11,249)	$ (9,793)	$ (11,249)