INCOME TAXES (Details 2) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income taxes
Income tax deductions	$ 85,700,000	$ 84,900,000	$ 65,200,000
Valuation allowance	0
Provisional ratepayer net refund	108,000,000
Unrecognized tax benefits that would impact effective tax rate	2,100,000
Reconciliation of the income tax expense computed by applying the current federal tax rate to pretax book income and the amount shown in the Consolidated Statements of Income
Statutory income tax	35,190,000	26,422,000	24,607,000
Increase (reduction) in taxes due to:
State income taxes net of federal tax benefit	5,781,000	4,341,000	4,043,000
Effect of regulatory treatment of fixed asset differences	(4,584,000)	(4,298,000)	(3,450,000)
Investment tax credits	(74,000)	(74,000)	(74,000)
AFUDC equity	(1,528,000)	0	0
Share base stock compensation	(581,000)	0	0
Other	(842,000)	425,000	163,000
Total income tax	33,362,000	$ 26,816,000	$ 25,289,000
State
Income taxes
Net operating loss resulting from repairs and maintenance deductions	55,400,000
Federal
Income taxes
Net operating loss resulting from repairs and maintenance deductions	72,600,000
California | State
Income taxes
State tax credits	4,200,000
Estimated carried-forward portion of tax credits	$ 2,300,000