LOANS AND ALLOWANCE FOR PROBABLE LOAN LOSSES - Interest Income on Impaired Loans (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Impaired Financing Receivable, Average Recorded Investment and Interest [Abstract]
Average Recorded Investment	$ 33,383	$ 9,504	$ 22,597
Interest Income Recognized	417	325	344
Construction Real Estate Loans
Impaired Financing Receivable, Average Recorded Investment and Interest [Abstract]
Average Recorded Investment	149	251	510
Interest Income Recognized	7	0	22
1-4 Family Residential Real Estate Loans
Impaired Financing Receivable, Average Recorded Investment and Interest [Abstract]
Average Recorded Investment	4,193	4,264	3,247
Interest Income Recognized	208	197	169
Commercial Real Estate Loans
Impaired Financing Receivable, Average Recorded Investment and Interest [Abstract]
Average Recorded Investment	26,186	1,338	4,490
Interest Income Recognized	65	30	63
Commercial Loans
Impaired Financing Receivable, Average Recorded Investment and Interest [Abstract]
Average Recorded Investment	2,131	2,862	13,481
Interest Income Recognized	102	59	48
Municipal Loans
Impaired Financing Receivable, Average Recorded Investment and Interest [Abstract]
Average Recorded Investment	474	545	612
Interest Income Recognized	26	30	33
Loans to Individuals
Impaired Financing Receivable, Average Recorded Investment and Interest [Abstract]
Average Recorded Investment	250	244	257
Interest Income Recognized	$ 9	$ 9	$ 9