INCOME TAXES - RECONCILIATION (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Effective tax rate that differs from that computed at the federal statutory rate
Federal corporate tax rate	21.00%	21.00%	21.00%	21.00%
Effect of:
State taxes, net of federal benefit (as a percent)	1.66%	(2.47%)	1.61%	(0.51%)
General business tax credits (as a percent)	(1.61%)	(0.55%)	(1.47%)	(0.68%)
Nontaxable income (as a percent)	(0.71%)	(1.27%)	(0.71%)	(0.89%)
Other, net (as a percent)	(0.98%)	(1.72%)	(0.36%)	(0.63%)
Effective tax rate (as a percent)	19.36%	14.99%	20.07%	18.29%