Employee Benefit Plans: (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Components of Net Periodic Benefits Cost:
Increase (Decrease) in Regulatory Assets and Liabilities			$ (367)	$ (19,112)
GOLDEN STATE WATER COMPANY
Components of Net Periodic Benefits Cost:
Increase (Decrease) in Regulatory Assets and Liabilities			582	(19,112)
Pension Benefits
Components of Net Periodic Benefits Cost:
Service cost	$ 1,390	$ 1,110	4,170	3,330
Interest cost	1,970	2,132	5,910	6,396
Expected return on plan assets	(2,950)	(2,594)	(8,850)	(7,782)
Amortization of prior service cost	109	109	327	327
Amortization of actuarial (gain) loss	484	355	1,452	1,065
Net periodic benefits costs under accounting standards	1,003	1,112	3,009	3,336
Increase (Decrease) in Regulatory Assets and Liabilities	(121)	(160)	(362)	(502)
Expected contributions in current fiscal year	3,700		3,700
Defined Benefit Plan, Net Periodic Benefit Cost before Allocation to Overhead Pool	882	952	2,647	2,834
Pension Benefits | GOLDEN STATE WATER COMPANY
Components of Net Periodic Benefits Cost:
Increase (Decrease) in Regulatory Assets and Liabilities				(502)
Regulatory adjustment — deferred	(1,100)		(1,100)
Pension Benefits | Bear Valley Electric Service, Inc.
Components of Net Periodic Benefits Cost:
Regulatory adjustment — deferred	(166)		(166)
Other Postretirement Benefits
Components of Net Periodic Benefits Cost:
Service cost	35	53	129	159
Interest cost	44	80	156	240
Expected return on plan assets	(130)	(112)	(384)	(336)
Amortization of prior service cost	0	0
Amortization of actuarial (gain) loss	(334)	(150)	(732)	(450)
Net periodic benefits costs under accounting standards	(385)	(129)	(831)	(387)
Increase (Decrease) in Regulatory Assets and Liabilities	0	0	0	0
Defined Benefit Plan, Net Periodic Benefit Cost before Allocation to Overhead Pool	(385)	(129)	(831)	(387)
SERP
Components of Net Periodic Benefits Cost:
Service cost	244	298	732	894
Interest cost	247	267	741	801
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	633	354
Net periodic benefits costs under accounting standards	702	683	2,106	2,049
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	$ 2,106	$ 2,049
Water Service Utility Operations [Member] | Pension Benefits | GOLDEN STATE WATER COMPANY
Components of Net Periodic Benefits Cost:
Increase (Decrease) in Regulatory Assets and Liabilities	$ (121)