ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) - Accumulated Other Comprehensive (loss) income (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Sep. 30, 2023	Sep. 30, 2022
Accumulated other comprehensive (loss) income, net of tax:
Balance	$ 1,202,503	$ 1,191,253	$ 1,169,583	$ 1,140,522	$ 1,155,287	$ 1,192,620	$ 1,169,583	$ 1,192,620
Total other comprehensive loss, net of tax	(2,528)	(5,747)	(4,259)	(23,086)	(20,570)	(43,199)	(12,534)	(86,855)
Balance	1,204,344	1,202,503	1,191,253	1,140,791	1,140,522	1,155,287	1,204,344	1,140,791
Accumulated Other Comprehensive Loss, Net of Deferred Taxes
Accumulated other comprehensive (loss) income, net of tax:
Balance	(104,385)	(98,638)	(94,379)	(69,950)	(49,380)	(6,181)	(94,379)	(6,181)
Other comprehensive (loss) income before reclassifications							(14,615)	(84,542)
Amounts reclassified from accumulated other comprehensive loss							2,081	(2,313)
Total other comprehensive loss, net of tax	(2,528)	(5,747)	(4,259)	(23,086)	(20,570)	(43,199)	(12,534)	(86,855)
Balance	(106,913)	$ (104,385)	(98,638)	(93,036)	$ (69,950)	(49,380)	(106,913)	(93,036)
Securities
Accumulated other comprehensive (loss) income, net of tax:
Balance			(100,870)			(7,864)	(100,870)	(7,864)
Other comprehensive (loss) income before reclassifications							(15,338)	(96,565)
Amounts reclassified from accumulated other comprehensive loss							2,666
Total other comprehensive loss, net of tax							(12,672)	(96,565)
Balance	(113,542)			(104,429)			(113,542)	(104,429)
Defined Benefit Plans
Accumulated other comprehensive (loss) income, net of tax:
Balance			(5,266)			(1,306)	(5,266)	(1,306)
Other comprehensive (loss) income before reclassifications							952	2,051
Amounts reclassified from accumulated other comprehensive loss							(781)	(1,923)
Total other comprehensive loss, net of tax							171	128
Balance	(5,095)			(1,178)			(5,095)	(1,178)
Derivatives
Accumulated other comprehensive (loss) income, net of tax:
Balance			$ 11,757			$ 2,989	11,757	2,989
Other comprehensive (loss) income before reclassifications							(229)	9,972
Amounts reclassified from accumulated other comprehensive loss							196	(390)
Total other comprehensive loss, net of tax							(33)	9,582
Balance	$ 11,724			$ 12,571			$ 11,724	$ 12,571