Employee Benefit Plans: (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Components of Net Periodic Benefits Cost:
Increase (Decrease) in Regulatory Assets and Liabilities			$ (19,112)	$ 22,945
GOLDEN STATE WATER COMPANY
Components of Net Periodic Benefits Cost:
Increase (Decrease) in Regulatory Assets and Liabilities			(19,112)	22,945
Pension Benefits
Components of Net Periodic Benefits Cost:
Service cost	$ 1,110	$ 1,335	3,330	4,005
Interest cost	2,132	1,912	6,396	5,736
Expected return on plan assets	(2,594)	(2,793)	(7,782)	(8,379)
Amortization of prior service cost	109	0	327	0
Amortization of actuarial (gain) loss	355	314	1,065	942
Net periodic benefits costs under accounting standards	1,112	768	3,336	2,304
Increase (Decrease) in Regulatory Assets and Liabilities	(160)	0	(502)	0
Expected contributions in current fiscal year	3,900		3,900
Defined Benefit Plan, Net Periodic Benefit Cost before Allocation to Overhead Pool	952	768	2,834	2,304
Pension Benefits | GOLDEN STATE WATER COMPANY
Components of Net Periodic Benefits Cost:
Increase (Decrease) in Regulatory Assets and Liabilities	(160)		(502)
Regulatory adjustment — deferred	(2,800)		(2,800)
Other Postretirement Benefits
Components of Net Periodic Benefits Cost:
Service cost	53	48	159	162
Interest cost	80	75	240	219
Expected return on plan assets	(112)	(123)	(336)	(369)
Amortization of prior service cost	0	0	0	0
Amortization of actuarial (gain) loss	(150)	(212)	(450)	(576)
Net periodic benefits costs under accounting standards	(129)	(212)	(387)	(564)
Increase (Decrease) in Regulatory Assets and Liabilities	0	0	0	0
Defined Benefit Plan, Net Periodic Benefit Cost before Allocation to Overhead Pool	(129)	(212)	(387)	(564)
SERP
Components of Net Periodic Benefits Cost:
Service cost	298	274	894	822
Interest cost	267	222	801	666
Expected return on plan assets	0	0	0	0
Amortization of prior service cost	0	0	0	0
Amortization of actuarial (gain) loss	118	262	354	786
Net periodic benefits costs under accounting standards	683	758	2,049	2,274
Increase (Decrease) in Regulatory Assets and Liabilities	0	0	0	0
Defined Benefit Plan, Net Periodic Benefit Cost before Allocation to Overhead Pool	$ 683	$ 758	$ 2,049	$ 2,274