Business Segments - Schedule of Business Segments (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2025	Jun. 30, 2025	Mar. 31, 2025	Sep. 30, 2024	Jun. 30, 2024	Mar. 31, 2024	Sep. 30, 2025	Sep. 30, 2024
Details of reportable segment
Total operating revenues	$ 182,716			$ 161,782			$ 493,795	$ 452,361
Supply costs	42,092			38,112			108,500	95,529
Other operation	11,782			11,021			34,582	31,377
Administrative and general	25,413			24,200			77,510	73,034
Depreciation and amortization	11,934			10,849			35,197	32,341
Maintenance	5,481			3,719			15,757	10,479
Property and other taxes	7,771			7,063			21,678	20,162
ASUS construction	16,510			11,750			42,333	43,649
Operating Income	61,733			55,068			158,238	145,790
Interest expense	(11,711)			(13,225)			(35,901)	(39,217)
Interest income	1,064			1,739			4,575	5,902
(Gain) loss on investments held in a trust	2,474			2,071			4,636	5,116
Income tax expense	12,925			10,056			31,622	27,811
Other segment items income (expense)	532			237			1,775	1,053
Net Income	41,167	$ 33,690	$ 26,844	35,834	$ 31,864	$ 23,135	101,701	90,833
Capital additions	54,646			64,179			173,127	173,477
Reportable Legal Entities
Details of reportable segment
Total operating revenues	182,716			161,782			493,795	452,361
Supply costs	42,092			38,112			108,500	95,529
Other operation	11,782			11,021			34,582	31,377
Administrative and general	25,411			24,198			77,505	73,029
Depreciation and amortization	11,934			10,849			35,197	32,341
Maintenance	5,481			3,719			15,757	10,479
Property and other taxes	7,771			7,063			21,678	20,162
ASUS construction	16,510			11,750			42,333	43,649
Operating Income	61,735			55,070			158,243	145,795
Interest expense	(9,843)			(11,833)			(31,266)	(34,467)
Interest income	1,052			1,712			4,535	5,829
(Gain) loss on investments held in a trust	2,474			2,071			4,636	5,116
Income tax expense	13,619			10,788			33,337	29,502
Other segment items income (expense)	476			237			1,310	796
Net Income	42,275			36,469			104,121	93,567
Capital additions	54,646			64,179			173,127	173,477
AWR | Intersegment Eliminations
Details of reportable segment
Total operating revenues	0			0			0	0
Supply costs	0			0			0	0
Other operation	0			0			0	0
Administrative and general	2			2			5	5
Depreciation and amortization	0			0			0	0
Maintenance	0			0			0	0
Property and other taxes	0			0			0	0
ASUS construction	0			0			0	0
Operating Income	(2)			(2)			(5)	(5)
Interest expense	(1,868)			(1,392)			(4,635)	(4,750)
Interest income	12			27			40	73
(Gain) loss on investments held in a trust	0			0			0	0
Income tax expense	(694)			(732)			(1,715)	(1,691)
Other segment items income (expense)	56			0			465	257
Net Income	(1,108)			(635)			(2,420)	(2,734)
Capital additions	0			0			0	0
GOLDEN STATE WATER COMPANY
Details of reportable segment
Total operating revenues	132,323			124,043			354,023	324,732
Other operation	8,044			7,807			23,519	21,829
Administrative and general	16,632			16,554			50,241	49,464
Depreciation and amortization	10,085			9,070			29,804	27,147
Maintenance	2,601			2,209			7,429	6,247
Property and other taxes	6,364			5,901			17,698	16,625
Operating Income	49,419			46,846			126,772	116,578
Interest expense	(8,552)			(9,862)			(27,145)	(28,970)
Interest income	511			1,504			2,719	4,589
(Gain) loss on investments held in a trust							4,636	5,116
Income tax expense	10,863			9,228			26,473	23,539
Net Income	33,298	$ 28,140	$ 19,906	31,566	$ 25,195	$ 17,794	81,344	74,555
GOLDEN STATE WATER COMPANY | Water:
Details of reportable segment
Total operating revenues	132,323			124,043			354,023	324,732
GOLDEN STATE WATER COMPANY | Reportable Legal Entities | Water:
Details of reportable segment
Total operating revenues	132,323			124,043			354,023	324,732
Supply costs	39,178			35,656			98,560	86,842
Other operation	8,044			7,807			23,519	21,829
Administrative and general	16,632			16,554			50,241	49,464
Depreciation and amortization	10,085			9,070			29,804	27,147
Maintenance	2,601			2,209			7,429	6,247
Property and other taxes	6,364			5,901			17,698	16,625
ASUS construction	0			0			0	0
Operating Income	49,419			46,846			126,772	116,578
Interest expense	(8,552)			(9,862)			(27,145)	(28,970)
Interest income	511			1,504			2,719	4,589
(Gain) loss on investments held in a trust	2,474			2,071			4,636	5,116
Income tax expense	10,863			9,228			26,473	23,539
Other segment items income (expense)	309			235			835	781
Net Income	33,298			31,566			81,344	74,555
Capital additions	47,518			51,466			148,597	147,093
BVES | Electric:
Details of reportable segment
Total operating revenues	13,332			9,040			41,262	29,948
BVES | Reportable Legal Entities | Electric:
Details of reportable segment
Total operating revenues	13,332			9,040			41,262	29,948
Supply costs	2,914			2,456			9,940	8,687
Other operation	1,179			797			3,499	2,716
Administrative and general	3,116			2,042			9,862	6,745
Depreciation and amortization	934			944			2,718	2,721
Maintenance	1,612			183			4,248	961
Property and other taxes	727			576			2,063	1,702
ASUS construction	0			0			0	0
Operating Income	2,850			2,042			8,932	6,416
Interest expense	(1,239)			(1,357)			(3,577)	(3,810)
Interest income	334			11			1,208	648
(Gain) loss on investments held in a trust	0			0			0	0
Income tax expense	400			135			1,532	656
Other segment items income (expense)	172			21			488	68
Net Income	1,717			582			5,519	2,666
Capital additions	5,498			11,862			19,480	23,023
ASUS | Reportable Legal Entities | Contracted services:
Details of reportable segment
Total operating revenues	37,061			28,699			98,510	97,681
Supply costs	0			0			0	0
Other operation	2,559			2,417			7,564	6,832
Administrative and general	5,663			5,602			17,402	16,820
Depreciation and amortization	915			835			2,675	2,473
Maintenance	1,268			1,327			4,080	3,271
Property and other taxes	680			586			1,917	1,835
ASUS construction	16,510			11,750			42,333	43,649
Operating Income	9,466			6,182			22,539	22,801
Interest expense	(52)			(614)			(544)	(1,687)
Interest income	207			197			608	592
(Gain) loss on investments held in a trust	0			0			0	0
Income tax expense	2,356			1,425			5,332	5,307
Other segment items income (expense)	(5)			(19)			(13)	(53)
Net Income	7,260			4,321			17,258	16,346
Capital additions	1,630			851			5,050	3,361
Golden State Water Company and Bear Valley Electric Service Inc.
Details of reportable segment
Depreciation on transportation equipment	$ 200			$ 200			$ 700	$ 500