Employee Benefit Plans: (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		6 Months Ended
	Jul. 31, 2018	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Pension Benefits
Components of Net Periodic Benefits Cost:
Service cost		$ 1,269	$ 1,249	$ 2,670	$ 2,500
Interest cost		1,903	1,985	3,824	3,952
Expected return on plan assets		(2,795)	(2,240)	(5,586)	(4,850)
Amortization of prior service cost (benefit)		0	0	0	0
Amortization of actuarial (gain) loss		283	253	628	462
Net periodic pension cost under accounting standards		660	1,247	1,536	2,064
Regulatory adjustment — deferred		0	(92)	0	(525)
Total expense recognized, before surcharges and allocation to overhead pool		660	1,339	1,536	2,589
Expected contributions in current fiscal year		6,100		6,100
Pension Benefits | GOLDEN STATE WATER COMPANY
Components of Net Periodic Benefits Cost:
Regulatory adjustment — deferred				2,200
Other Postretirement Benefits
Components of Net Periodic Benefits Cost:
Service cost		57	59	114	118
Interest cost		72	85	144	170
Expected return on plan assets		(123)	(122)	(246)	(244)
Amortization of prior service cost (benefit)		0	0	0	0
Amortization of actuarial (gain) loss		(182)	(170)	(364)	(340)
Net periodic pension cost under accounting standards		(176)	(148)	(352)	(296)
Regulatory adjustment — deferred		0	0	0	0
Total expense recognized, before surcharges and allocation to overhead pool		(176)	(148)	(352)	(296)
SERP
Components of Net Periodic Benefits Cost:
Service cost		274	232	548	464
Interest cost		222	223	444	446
Expected return on plan assets		0	0	0	0
Amortization of prior service cost (benefit)		0	3	0	6
Amortization of actuarial (gain) loss		262	194	524	388
Net periodic pension cost under accounting standards		758	652	1,516	1,304
Regulatory adjustment — deferred		0	0	0	0
Total expense recognized, before surcharges and allocation to overhead pool		$ 758	$ 652	$ 1,516	$ 1,304
Subsequent Event [Member]
Pension Plan's funded status and amounts recognized in balance sheets and the components of net pension cost and accrued post-retirement liability
Defined Benefit Plan, Plan Assets, Contributions by Employer	$ 1,000