Employee Benefit Plans: (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Pension Benefits
Components of Net Periodic Benefits Cost:
Service cost	$ 1,234	$ 1,401
Interest cost	2,131	1,921
Expected return on plan assets	(2,593)	(2,791)
Amortization of prior service cost (benefit)	109	0
Amortization of actuarial (gain) loss	359	345
Total expense recognized, before surcharges and allocation to overhead pool	1,240	876
Expected contributions in current fiscal year	3,600
Pension Benefits | GOLDEN STATE WATER COMPANY
Components of Net Periodic Benefits Cost:
Regulatory adjustment — deferred	(3,100)
Other Postretirement Benefits
Components of Net Periodic Benefits Cost:
Service cost	53	57
Interest cost	80	72
Expected return on plan assets	(112)	(123)
Amortization of prior service cost (benefit)	0	0
Amortization of actuarial (gain) loss	(150)	(182)
Total expense recognized, before surcharges and allocation to overhead pool	(129)	(176)
SERP
Components of Net Periodic Benefits Cost:
Service cost	298	274
Interest cost	267	222
Expected return on plan assets	0	0
Amortization of prior service cost (benefit)	0	0
Amortization of actuarial (gain) loss	118	262
Total expense recognized, before surcharges and allocation to overhead pool	$ 683	$ 758