INCOME TAXES (Details 2) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Income taxes
Unrecognized tax benefits	$ 612,000	$ 0	$ 831,000	$ 831,000
Valuation allowance	0
Additional first year bonus depreciation (as a percent)	50.00%
Deferred tax liability bonus depreciation	231,141,000	207,642,000
Effect of regulatory treatment of fixed asset differences	(4,112,000)	(7,030,000)	(1,614,000)
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
Computed expected tax expense	23,708,000	24,600,000	21,308,000
Increase (reduction) in taxes due to:
State income taxes net of federal tax benefit	3,895,000	4,041,000	3,500,000
Effect of regulatory treatment of fixed asset differences	(4,112,000)	(7,030,000)	(1,614,000)
State tax credits	(2,465,000)
Investment tax credits	(74,000)	(74,000)	(74,000)
Other	(483,000)	(85,000)	46,000
Total	20,469,000	21,452,000	23,166,000
2012 and prior years
Income taxes
Effect of regulatory treatment of fixed asset differences	(3,061,000)
Increase (reduction) in taxes due to:
Effect of regulatory treatment of fixed asset differences	(3,061,000)
State
Income taxes
Net operating loss resulting from repairs and maintenance deductions	42,000,000
State | 2012 and prior years
Income taxes
Income tax deductions		41,000,000
Increase (decrease) in income tax expense		(2,400,000)
State | 2011 and prior years
Income taxes
Income tax deductions			122,200,000
Increase (decrease) in income tax expense			(7,000,000)
Federal
Income taxes
Income tax deductions	2,100,000	5,100,000	12,600,000
Increase (decrease) in income tax expense		800,000
Net operating loss resulting from repairs and maintenance deductions	14,800,000
Deferred tax liability bonus depreciation	2,100,000	5,000,000
Current federal tax rate (as a percent)	35.00%
Federal | 2012 and prior years
Income taxes
Income tax deductions		25,000,000
Deferred income tax Liability	8,800,000
Federal | 2011 and prior years
Income taxes
Income tax deductions			86,700,000
Deferred income tax Liability		30,400,000
State of California | State
Income taxes
Tax credits	4,400,000
Tax credit carry-forward period	10 years
Estimated carried-forward portion of tax credits	2,300,000
Unrecognized tax benefits	600,000
Increase (decrease) in income tax expense			$ (1,600,000)