LOANS AND ALLOWANCE FOR PROBABLE LOAN LOSSES - Purchased Credit Impaired (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Purchased Credit Impaired [Abstract]
Outstanding principal balance	$ 41,858	$ 51,388
Carrying amount	37,807	46,402
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield Movement Schedule [Roll Forward]
Balance at beginning of period	15,054	18,721	$ 2,480
Additions due to acquisition	0	0	15,389
Changes in expected cash flows not affecting non-accretable differences	0	(1,445)	0
Reclassifications (to) from nonaccretable discount	1,354	1,211	1,720
Accretion	(2,988)	(3,433)	(868)
Balance at end of period	$ 13,420	$ 15,054	$ 18,721