LOANS AND ALLOWANCE FOR PROBABLE LOAN LOSSES - Nonperforming Assets by Asset Class (Details) - USD ($) $ in Thousands		Dec. 31, 2019	Dec. 31, 2018
Nonperforming Assets by Asset Class [Abstract]
Nonaccrual loans	[1],[2]	$ 4,963	$ 35,770
Accruing loans past due more than 90 days	[2]	0	0
Restructured loans	[3]	12,014	5,930
Other real estate owned		472	1,206
Repossessed assets		0	0
Total nonperforming assets		17,449	42,906
Restructured nonaccrual loans		469	10,900
PCI loans restructured		$ 755	$ 3,100

[1] Includes $469,000 and $10.9 million of restructured loans as of December 31, 2019 and 2018, respectively.

[2] Excludes PCI loans measured at fair value at acquisition if the timing and amount of cash flows expected to be collected from those sales can be reasonably estimated.

[3] Includes $755,000 and $3.1 million in PCI loans restructured as of December 31, 2019 and 2018, respectively.