Taxes on Income (Details) - USD ($)	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Taxes on income
Unrecognized Tax Benefits	$ 0	$ 0	$ 0
Deferred tax assets:
Regulatory-liability-related	31,330,000	32,220,000
Contributions and advances	6,544,000	6,850,000
Deferred Tax Assets, Other	7,424,000	5,324,000
Deferred tax assets	45,298,000	44,394,000
Deferred tax liabilities:
Fixed assets	(155,955,000)	(150,290,000)
Regulatory-asset-related: depreciation and other	(30,226,000)	(25,914,000)
Balancing and memorandum accounts (non-flow-through)	(8,794,000)	(8,480,000)
Deferred tax liabilities	(194,975,000)	(184,684,000)
Accumulated deferred income taxes - net	(149,677,000)	(140,290,000)
Current
Federal	14,845,000	19,592,000	19,240,000
State	6,016,000	7,270,000	6,714,000
Total current tax expense	20,861,000	26,862,000	25,954,000
Deferred
Federal	2,991,000	2,802,000	1,814,000
State	(188,000)	759,000	429,000
Total deferred tax (benefit) expense	2,803,000	3,561,000	2,243,000
Reconciliations of the effective tax rates to the federal statutory rate
Federal taxes on pretax income at statutory rate (21% in 2018; 35% in 2017 and 2016)	21,433,000	26,202,000	24,071,000
Increase (decrease) in taxes resulting from:	4,335,000	6,425,000	5,764,000
Excess deferred tax amortization	(1,311,000)	(1,356,000)	(1,550,000)
Flow-through on fixed assets	1,076,000	1,069,000	1,056,000
Flow-through on removal costs	(1,802,000)	(1,962,000)	(1,031,000)
Investment tax credit	(71,000)	(71,000)	(71,000)
Other- net	4,000	116,000	(42,000)
Total income tax expense operations	23,664,000	30,423,000	28,197,000
Income before income tax expense	$ 102,060,000	$ 124,770,000	$ 114,622,000
Effective income tax rate (as a percent)	23.20%	24.40%	24.60%
GSWC
Deferred tax assets:
Regulatory-liability-related	$ 29,623,000	$ 30,410,000
Contributions and advances	6,896,000	7,227,000
Deferred Tax Assets, Other	7,874,000	5,689,000
Deferred tax assets	44,393,000	43,326,000
Deferred tax liabilities:
Fixed assets	(150,133,000)	(144,719,000)
Regulatory-asset-related: depreciation and other	(28,489,000)	(24,858,000)
Balancing and memorandum accounts (non-flow-through)	(4,559,000)	(6,063,000)
Deferred tax liabilities	(183,181,000)	(175,640,000)
Accumulated deferred income taxes - net	(138,788,000)	(132,314,000)
Current
Federal	10,582,000	13,698,000	$ 14,674,000
State	4,909,000	6,089,000	5,849,000
Total current tax expense	15,491,000	19,787,000	20,523,000
Deferred
Federal	1,507,000	2,251,000	949,000
State	(652,000)	57,000	232,000
Total deferred tax (benefit) expense	855,000	2,308,000	1,181,000
Reconciliations of the effective tax rates to the federal statutory rate
Federal taxes on pretax income at statutory rate (21% in 2018; 35% in 2017 and 2016)	14,724,000	19,175,000	18,202,000
Increase (decrease) in taxes resulting from:	3,119,000	4,923,000	4,920,000
Excess deferred tax amortization	(1,130,000)	(1,184,000)	(1,477,000)
Flow-through on fixed assets	1,010,000	1,008,000	1,042,000
Flow-through on removal costs	(1,715,000)	(1,954,000)	(1,026,000)
Investment tax credit	(71,000)	(71,000)	(71,000)
Other- net	409,000	198,000	114,000
Total income tax expense operations	16,346,000	22,095,000	21,704,000
Income before income tax expense	70,116,000	91,310,000	86,675,000
Pretax income from operations	$ 70,116,000	$ 91,310,000	$ 86,675,000
Effective income tax rate (as a percent)	23.30%	24.20%	25.00%