INCOME TAXES (Details 3) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Deferred tax assets:
Developer deposits for extension agreements and contributions in aid of construction	$ 46,318	$ 45,670
Net operating loss carryforward and tax credits	12,348	15,042
Pension	9,865	7,922
Other	5,651	3,341
Total deferred tax assets	74,182	71,975
Deferred tax liabilities:
Property related basis and depreciation differences	347,071	309,088
WRAM/MCBA and interim rates balancing accounts	20,714	23,894
Other	5,321	3,890
Total deferred tax liabilities	373,106	336,872
Total deferred tax liabilities	298,924	264,897
Reconciliation of the changes in unrecognized tax benefits
Balance at beginning of year	10,298	7,916	$ 612
Additions for tax positions taken during prior year	0	0	7,304
Additions for tax positions taken during current year	201	2,382
Reductions for tax positions taken during a prior year	0	0	0
Lapse of statute of limitations	0	0	0
Balance at end of year	$ 10,499	$ 10,298	$ 7,916