Employee Benefit Plans: (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Pension Benefits
Components of Net Periodic Benefits Cost:
Service cost	$ 1,401	$ 1,251
Interest cost	1,921	1,967
Expected return on plan assets	(2,791)	(2,610)
Amortization of prior service cost (benefit)	0	0
Amortization of actuarial (gain) loss	345	209
Net periodic pension cost under accounting standards	876	817
Regulatory adjustment — deferred	0	433
Total expense recognized, before surcharges and allocation to overhead pool	876	1,250
Expected contributions in current fiscal year	6,100
Pension Benefits | GOLDEN STATE WATER COMPANY
Components of Net Periodic Benefits Cost:
Regulatory adjustment — deferred	(2,100)
Other Postretirement Benefits
Components of Net Periodic Benefits Cost:
Service cost	57	59
Interest cost	72	85
Expected return on plan assets	(123)	(122)
Amortization of prior service cost (benefit)	0	0
Amortization of actuarial (gain) loss	(182)	(170)
Net periodic pension cost under accounting standards	(176)	(148)
Regulatory adjustment — deferred	0	0
Total expense recognized, before surcharges and allocation to overhead pool	(176)	(148)
SERP
Components of Net Periodic Benefits Cost:
Service cost	274	232
Interest cost	222	223
Expected return on plan assets	0	0
Amortization of prior service cost (benefit)	0	3
Amortization of actuarial (gain) loss	262	194
Net periodic pension cost under accounting standards	758	652
Regulatory adjustment — deferred	0	0
Total expense recognized, before surcharges and allocation to overhead pool	$ 758	$ 652