INCOME TAXES (Reconciliation of Differences between Income Tax Expense and Amount Obtained by Multiplying Pre-Tax Income by U.S. Statutory Federal Income Tax Rate) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Federal Income Tax Expense at Statutory Rate	$ 46,000	$ 49,000	$ 97,000
State Income Tax Expense, Net of Federal Deduction	9,000	9,000	9,000
Federal/State Tax Credits	(6,000)	(10,000)	(9,000)
Allowance for Equity Funds Used During Construction	(3,000)	(1,000)	(2,000)
Impact of Enactment, TCJA	0	0	7,000
Excess Deferred Income Taxes	(9,000)	(6,000)	0
Impact of AMT Sequestration	(2,000)	2,000	0
Other	(1,000)	0	(1,000)
Total Federal and State Income Tax Expense	$ 34,053	$ 42,982	$ 100,763