ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) - Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance	$ 1,172,824	$ 701,096	$ 645,648	$ 596,758	$ 701,096	$ 596,758
Other comprehensive (loss) income before reclassifications					11,310	(7,368)
Amounts reclassified from accumulated other comprehensive loss					(810)	(1,095)
Total other comprehensive income	4,045	6,455	(1,771)	(6,692)	10,500	(8,463)
Balance	1,204,276	1,172,824	681,543	645,648	1,204,276	681,543
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance	531	(5,924)	(12,632)	(5,940)	(5,924)	(5,940)
Total other comprehensive income	4,045	6,455	(1,771)	(6,692)
Balance	4,576	531	(14,403)	(12,632)	4,576	(14,403)
Securities Available-for-Sale
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance		12,694		4,621	12,694	4,621
Other comprehensive (loss) income before reclassifications					(4,451)	9,609
Amounts reclassified from accumulated other comprehensive loss					(812)	(2,154)
Total other comprehensive income					(5,263)	7,455
Balance	7,431		12,076		7,431	12,076
Defined Benefit Plans
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance		(6,086)		(6,024)	(6,086)	(6,024)
Other comprehensive (loss) income before reclassifications					2,061	241
Amounts reclassified from accumulated other comprehensive loss					(579)	130
Total other comprehensive income					1,482	371
Balance	(4,604)		(5,653)		(4,604)	(5,653)
Derivatives
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance		$ (12,532)		$ (4,537)	(12,532)	(4,537)
Other comprehensive (loss) income before reclassifications					13,700	(17,218)
Amounts reclassified from accumulated other comprehensive loss					581	929
Total other comprehensive income					14,281	(16,289)
Balance	$ 1,749		$ (20,826)		$ 1,749	$ (20,826)