INCOME TAXES - RECONCILIATION OF EFFECTIVE TAX RATES (Details)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Reconciliation of effective tax rates and federal statutory rates applied to financial statement income
U. S. federal income tax rate (as a percent)	21.00%	21.00%
Changes from the statutory rate
State deferred tax benefit (as a percent)	(4.30%)
Tax-exempt interest income (as a percent)	(3.30%)	(4.40%)
Tax-exempt BOLI income (as a percent)	(0.70%)	(0.40%)
Historic and low income tax credits (as a percent)	(3.90%)	(4.00%)
Insurance captive (as a percent)	(1.10%)	(1.00%)
Non-deductible interest expense related to carrying tax-exempt investments (as a percent)	0.20%	0.20%
Other (as a percent)	(0.30%)	0.40%
Effective tax rates (as a percent)	7.60%	11.70%