INCOME TAXES INCOME TAXES (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Operating Loss Carryforwards [Line Items]
Federal tax rate, percentage			21.00%	35.00%
Federal Income Tax Expense at Statutory Rate	$ 25,000	$ 44,000	$ 45,000	$ 87,000
State Income Tax Expense, Net of Federal Deduction	4,000	4,000	8,000	8,000
Federal/State Tax Credits	(4,000)	(4,000)	(7,000)	(8,000)
Excess Deferred Income Taxes	(4,000)	0	(8,000)	0
Other	(2,000)	(2,000)	(2,000)	(3,000)
Total Federal and State Income Tax Expense	19,120	$ 42,100	35,521	$ 83,951
EDIT balance related to the effects of the TCJA included in Regulatory Liabilities	336,000		336,000
Internal Revenue Service (IRS)
Operating Loss Carryforwards [Line Items]
Tax credit carryforward, amount	$ 13,000		$ 13,000