Employee Benefit Plans: (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Components of Net Periodic Benefits Cost:
Regulatory adjustment — deferred			$ 712,000	$ 994,000
GSWC
Components of Net Periodic Benefits Cost:
Regulatory adjustment — deferred			712,000	994,000
Pension Benefits
Components of Net Periodic Benefits Cost:
Service cost	1,335,000	1,620,000	2,822,000	3,484,000
Interest cost	1,845,000	1,723,000	3,760,000	3,454,000
Expected return on plan assets	(2,235,000)	(1,895,000)	(4,450,000)	(3,788,000)
Amortization of transition	0	0	0	0
Amortization of prior service cost (benefit)	29,000	30,000	59,000	60,000
Amortization of actuarial (gain) loss	(7,000)	729,000	0	1,440,000
Net periodic pension cost under accounting standards	967,000	2,207,000	2,191,000	4,650,000
Regulatory adjustment — deferred	449,000	(409,000)	749,000	(919,000)
Total expense recognized, before allocation to overhead pool	1,416,000	1,798,000	2,940,000	3,731,000
Pension Benefits | GSWC
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, Expected Contributions in Current Fiscal Year			8,200,000
Components of Net Periodic Benefits Cost:
Regulatory adjustment — deferred			3,600,000
Other Postretirement Benefits
Components of Net Periodic Benefits Cost:
Service cost	99,000	106,000	198,000	212,000
Interest cost	130,000	113,000	260,000	226,000
Expected return on plan assets	(113,000)	(95,000)	(226,000)	(190,000)
Amortization of transition	104,000	105,000	208,000	210,000
Amortization of prior service cost (benefit)	(50,000)	(50,000)	(100,000)	(100,000)
Amortization of actuarial (gain) loss	(66,000)	0	(132,000)	0
Net periodic pension cost under accounting standards	104,000	179,000	208,000	358,000
Regulatory adjustment — deferred	0	0	0	0
Total expense recognized, before allocation to overhead pool	104,000	179,000	208,000	358,000
SERP
Components of Net Periodic Benefits Cost:
Service cost	192,000	201,000	384,000	402,000
Interest cost	154,000	129,000	308,000	258,000
Expected return on plan assets	0	0	0	0
Amortization of transition	0	0	0	0
Amortization of prior service cost (benefit)	40,000	40,000	80,000	80,000
Amortization of actuarial (gain) loss	35,000	85,000	70,000	170,000
Net periodic pension cost under accounting standards	421,000	455,000	842,000	910,000
Regulatory adjustment — deferred	0	0	0	0
Total expense recognized, before allocation to overhead pool	$ 421,000	$ 455,000	$ 842,000	$ 910,000