LOANS, ALLOWANCE FOR LOAN LOSSES, AND CREDIT QUALITY - Summary of Non-accredtable discount on purchase credit impaired ("PCI") loans (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Accretion Discount [Roll Forward]
Balance at beginning of period	$ 9,471	$ 14,327
Acquired balance, net	0	8,352
Accretion to loan interest income	(1,976)	(7,995)
Transferred to accretable	(990)	(1,936)
Disposals of loans	(97)	(3,277)
Balance at end of period	$ 6,408	$ 9,471