ACCUMULATED OTHER COMPREHENSIVE INCOME/ (LOSS) - Net Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	$ 1,588,142	$ 1,483,768
Other comprehensive loss before reclassification from accumulated other comprehensive loss, net of tax	(5,749)	15,490
Reclassifications from accumulated other comprehensive loss to earnings, net of tax	277	470
Total other comprehensive income/ (loss)	(5,472)	15,960
Balance at end of period	1,589,364	1,536,865
Total
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(97,331)	(131,951)
Total other comprehensive income/ (loss)	(5,472)	15,960
Balance at end of period	(102,803)	(115,991)
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	(5,749)	15,490
Reclassifications from accumulated other comprehensive loss to earnings, net of tax	0	0
Total other comprehensive income/ (loss)	(5,749)	15,490
Balance at end of period	(93,918)	(98,023)
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	168
Total other comprehensive income/ (loss)	0	168
Balance at end of period	0	(7,834)
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	277	302
Total other comprehensive income/ (loss)	277	302
Balance at end of period	$ (8,885)	$ (10,134)