INCOME TAXES - Effective Income Tax Rate Reconciliation (Details)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Federal income taxes statutory rate percentage	35.00%	35.00%	35.00%
Increases (reductions) resulting from:
State taxes, net of federal benefit percentage	4.20%	1.40%	1.30%
Amortization of investment tax credits related to rate-regulated assets percentage	(0.10%)	(0.20%)	(0.20%)
Other percentage	0.20%	(1.10%)	0.60%
Effective income tax rate percentage	39.30%	35.10%	36.70%