INCOME TAXES (Details 3) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Deferred tax assets:
Developer deposits for extension agreements and contributions in aid of construction	$ 33,552	$ 46,318
Net operating loss carryforward and tax credits	13,329	12,348
Pension	7,906	9,865
Income tax regulatory liability	41,712	0
Other	280	5,651
Total deferred tax assets	96,779	74,182
Deferred tax liabilities:
Property related basis and depreciation differences	262,442	347,071
WRAM/MCBA and interim rates balancing accounts	24,733	20,714
Other	2,550	5,321
Total deferred tax liabilities	289,725	373,106
Total deferred tax liabilities	192,946	298,924
Reconciliation of the changes in unrecognized tax benefits
Balance at beginning of year	10,499	10,298	$ 7,916
Additions for tax positions taken during prior year	0	0	0
Additions for tax positions taken during current year	559	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	$ 11,058	$ 10,499	$ 10,298