ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) - Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance	$ 701,096	$ 596,758
Other comprehensive income (loss) before reclassifications	7,565	(6,891)
Amounts reclassified from accumulated other comprehensive loss	(1,110)	199
Other comprehensive income (loss), net of tax	6,455	(6,692)
Balance	1,172,824	645,648
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance	(5,924)	(5,940)
Other comprehensive income (loss), net of tax	6,455	(6,692)
Balance	531	(12,632)
Securities Available-for-Sale
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance	12,694	4,621
Other comprehensive income (loss) before reclassifications	(10,570)	7,049
Amounts reclassified from accumulated other comprehensive loss	(822)	(5)
Other comprehensive income (loss), net of tax	(11,392)	7,044
Balance	1,302	11,665
Defined Benefit Plans
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance	(6,086)	(6,024)
Other comprehensive income (loss) before reclassifications	1,659	120
Amounts reclassified from accumulated other comprehensive loss	(288)	65
Other comprehensive income (loss), net of tax	1,371	185
Balance	(4,715)	(5,839)
Derivatives
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance	(12,532)	(4,537)
Other comprehensive income (loss) before reclassifications	16,476	(14,060)
Amounts reclassified from accumulated other comprehensive loss		139
Other comprehensive income (loss), net of tax	16,476	(13,921)
Balance	$ 3,944	$ (18,458)