Employee Benefit Plans: (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Components of Net Periodic Benefits Cost:
Increase (Decrease) in Regulatory Assets and Liabilities			$ (6,995)	$ (13,932)
GOLDEN STATE WATER COMPANY
Components of Net Periodic Benefits Cost:
Increase (Decrease) in Regulatory Assets and Liabilities			(6,995)	(13,932)
Pension Benefits
Components of Net Periodic Benefits Cost:
Service cost	$ 1,372	$ 986	2,780	2,220
Interest cost	1,986	2,133	3,940	4,264
Expected return on plan assets	(2,950)	(2,595)	(5,900)	(5,188)
Amortization of prior service cost	109	109	218	218
Amortization of actuarial (gain) loss	526	351	968	710
Net periodic benefits costs under accounting standards	1,043	984	2,006	2,224
Increase (Decrease) in Regulatory Assets and Liabilities	(148)	(342)	(241)	(342)
Expected contributions in current fiscal year	3,700		3,700
Defined Benefit Plan, Net Periodic Benefit Cost before Allocation to Overhead Pool	895	642	1,765	1,882
Pension Benefits | GOLDEN STATE WATER COMPANY
Components of Net Periodic Benefits Cost:
Increase (Decrease) in Regulatory Assets and Liabilities		(342)		(342)
Regulatory adjustment — deferred	(1,400)		(1,400)
Other Postretirement Benefits
Components of Net Periodic Benefits Cost:
Service cost	47	53	94	106
Interest cost	56	80	112	160
Expected return on plan assets	(127)	(112)	(254)	(224)
Amortization of prior service cost	0	0
Amortization of actuarial (gain) loss	(199)	(150)	(398)	(300)
Net periodic benefits costs under accounting standards	(223)	(129)	(446)	(258)
Increase (Decrease) in Regulatory Assets and Liabilities	0	0	0	0
Defined Benefit Plan, Net Periodic Benefit Cost before Allocation to Overhead Pool	(223)	(129)	(446)	(258)
SERP
Components of Net Periodic Benefits Cost:
Service cost	244	298	488	596
Interest cost	247	267	494	534
Expected return on plan assets	0	0	0	0
Amortization of prior service cost	0	0	0	0
Amortization of actuarial (gain) loss	211	118	422	236
Net periodic benefits costs under accounting standards	702	683	1,404	1,366
Increase (Decrease) in Regulatory Assets and Liabilities	0	0	0	0
Defined Benefit Plan, Net Periodic Benefit Cost before Allocation to Overhead Pool	702	$ 683	$ 1,404	$ 1,366
Water Service Utility Operations [Member] | Pension Benefits | GOLDEN STATE WATER COMPANY
Components of Net Periodic Benefits Cost:
Increase (Decrease) in Regulatory Assets and Liabilities	$ 148