ACCUMULATED OTHER COMPREHENSIVE INCOME/ (LOSS) - Net Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	$ 1,589,364	$ 1,536,865	$ 1,588,142	$ 1,483,768
Other comprehensive loss before reclassification from accumulated other comprehensive loss, net of tax			(5,212)	5,347
Reclassifications from accumulated other comprehensive loss to earnings, net of tax			549	979
Total other comprehensive income/ (loss)	809	(9,634)	(4,663)	6,326
Balance at end of period	1,599,004	1,539,032	1,599,004	1,539,032
Total
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(102,803)	(115,991)	(97,331)	(131,951)
Total other comprehensive income/ (loss)	809	(9,634)	(4,663)	6,326
Balance at end of period	(101,994)	(125,625)	(101,994)	(125,625)
Unrealized Gains/(Losses) on Debt Securities Available-for-Sale
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period			(88,169)	(113,513)
Other comprehensive loss before reclassification from accumulated other comprehensive loss, net of tax			(5,212)	5,347
Reclassifications from accumulated other comprehensive loss to earnings, net of tax			0	0
Total other comprehensive income/ (loss)			(5,212)	5,347
Balance at end of period	(93,381)	(108,166)	(93,381)	(108,166)
Defined Benefit Pension Plan
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period			0	(8,002)
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			0	336
Total other comprehensive income/ (loss)			0	336
Balance at end of period	0	(7,666)	0	(7,666)
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			(9,162)	(10,436)
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			549	643
Total other comprehensive income/ (loss)			549	643
Balance at end of period	$ (8,613)	$ (9,793)	$ (8,613)	$ (9,793)