ACCUMULATED OTHER COMPREHENSIVE LOSS - Net Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	$ 1,483,768	$ 1,519,679
Other comprehensive loss before reclassification from accumulated other comprehensive loss, net of tax	15,490
Reclassifications from accumulated other comprehensive loss to earnings, net of tax	470
Total other comprehensive income/ (loss)	15,960	(60,732)
Balance at end of period	1,536,865	1,488,910
Total
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(131,951)	(8,539)
Other comprehensive loss before reclassification from accumulated other comprehensive loss, net of tax		(61,109)
Reclassifications from accumulated other comprehensive loss to earnings, net of tax		377
Total other comprehensive income/ (loss)	15,960	(60,732)
Balance at end of period	(115,991)	(69,271)
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	15,490	(49,026)
Reclassifications from accumulated other comprehensive loss to earnings, net of tax	0	(6)
Total other comprehensive income/ (loss)	15,490	(49,032)
Balance at end of period	(98,023)	(49,368)
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	168	146
Total other comprehensive income/ (loss)	168	146
Balance at end of period	(7,834)	(8,057)
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	302	237
Total other comprehensive income/ (loss)	302	(11,846)
Balance at end of period	$ (10,134)	$ (11,846)