Business Segments - Schedule of Business Segments (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2026	Mar. 31, 2026	Jun. 30, 2025	Mar. 31, 2025	Jun. 30, 2026	Jun. 30, 2025
Details of reportable segment
Total operating revenues	$ 181,290		$ 163,066		$ 350,481	$ 311,079
Supply costs	37,525		36,920		72,183	66,408
Other operation	12,034		12,310		23,302	22,800
Administrative and general	24,521		25,222		52,675	52,097
Depreciation and amortization	12,747		11,681		25,431	23,263
Maintenance	6,201		6,129		11,901	10,276
Property and other taxes	7,544		6,955		15,567	13,907
ASUS construction expense	16,747		12,890		34,080	25,823
Operating Income	63,971		50,959		115,342	96,505
Interest expense	(12,174)		(12,108)		(24,281)	(24,190)
Interest income	886		1,498		1,862	3,511
(Gain) loss on investments held in a trust	4,330		2,748		3,058	2,161
Income tax expense	14,479		10,235		24,351	18,697
Other segment items income (expense)	740		828		1,592	1,244
Net Income	43,274	$ 29,948	33,690	$ 26,844	73,222	60,534
Capital additions	48,510		50,916		97,561	118,481
Reportable Legal Entities
Details of reportable segment
Total operating revenues	181,290		163,066		350,481	311,079
Supply costs	37,525		36,920		72,183	66,408
Other operation	12,034		12,310		23,302	22,800
Administrative and general	24,519		25,220		52,671	52,094
Depreciation and amortization	12,747		11,681		25,431	23,263
Maintenance	6,201		6,129		11,901	10,276
Property and other taxes	7,544		6,955		15,567	13,907
ASUS construction expense	16,747		12,890		34,080	25,823
Operating Income	63,973		50,961		115,346	96,508
Interest expense	(10,948)		(10,646)		(21,664)	(21,423)
Interest income	873		1,488		1,841	3,483
(Gain) loss on investments held in a trust	4,330		2,748		3,058	2,161
Income tax expense	15,128		10,780		25,465	19,718
Other segment items income (expense)	679		419		1,474	835
Net Income	43,779		34,190		74,590	61,846
Capital additions	48,510		50,916		97,561	118,481
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		4	3
Depreciation and amortization	0		0		0	0
Maintenance	0		0		0	0
Property and other taxes	0		0		0	0
ASUS construction expense	0		0		0	0
Operating Income	(2)		(2)		(4)	(3)
Interest expense	(1,226)		(1,462)		(2,617)	(2,767)
Interest income	13		10		21	28
(Gain) loss on investments held in a trust	0		0		0	0
Income tax expense	(649)		(545)		(1,114)	(1,021)
Other segment items income (expense)	61		409		118	409
Net Income	(505)		(500)		(1,368)	(1,312)
Capital additions	0		0		0	0
GOLDEN STATE WATER COMPANY
Details of reportable segment
Total operating revenues	131,050		119,697		244,160	221,700
Other operation	8,111		8,800		15,255	15,475
Administrative and general	15,337		15,952		33,091	33,609
Depreciation and amortization	10,733		9,895		21,392	19,719
Maintenance	3,005		2,824		5,079	4,828
Property and other taxes	6,198		5,710		12,718	11,334
Operating Income	52,969		42,557		91,667	77,353
Interest expense	(9,618)		(9,265)		(19,010)	(18,593)
Interest income	419		936		897	2,208
(Gain) loss on investments held in a trust					3,058	2,161
Income tax expense	12,642		9,096		20,206	15,610
Net Income	36,101	$ 21,683	28,140	$ 19,906	57,784	48,046
GOLDEN STATE WATER COMPANY | Water:
Details of reportable segment
Total operating revenues	131,050		119,697		244,160	221,700
GOLDEN STATE WATER COMPANY | Reportable Legal Entities | Water:
Details of reportable segment
Total operating revenues	131,050		119,697		244,160	221,700
Supply costs	34,697		33,959		64,958	59,382
Other operation	8,111		8,800		15,255	15,475
Administrative and general	15,337		15,952		33,091	33,609
Depreciation and amortization	10,733		9,895		21,392	19,719
Maintenance	3,005		2,824		5,079	4,828
Property and other taxes	6,198		5,710		12,718	11,334
ASUS construction expense	0		0		0	0
Operating Income	52,969		42,557		91,667	77,353
Interest expense	(9,618)		(9,265)		(19,010)	(18,593)
Interest income	419		936		897	2,208
(Gain) loss on investments held in a trust	4,330		2,748		3,058	2,161
Income tax expense	12,642		9,096		20,206	15,610
Other segment items income (expense)	643		260		1,378	527
Net Income	36,101		28,140		57,784	48,046
Capital additions	42,989		43,221		85,233	101,079
BVES | Electric:
Details of reportable segment
Total operating revenues	13,626		12,928		32,283	27,930
BVES | Reportable Legal Entities | Electric:
Details of reportable segment
Total operating revenues	13,626		12,928		32,283	27,930
Supply costs	2,828		2,961		7,225	7,026
Other operation	1,235		1,079		2,576	2,320
Administrative and general	3,183		3,648		6,849	6,746
Depreciation and amortization	1,068		899		2,134	1,784
Maintenance	1,559		1,725		3,809	2,636
Property and other taxes	750		650		1,572	1,336
ASUS construction expense	0		0		0	0
Operating Income	3,003		1,966		8,118	6,082
Interest expense	(1,291)		(1,202)		(2,544)	(2,338)
Interest income	253		350		543	874
(Gain) loss on investments held in a trust	0		0		0	0
Income tax expense	502		85		1,386	1,132
Other segment items income (expense)	29		147		74	316
Net Income	1,492		1,176		4,805	3,802
Capital additions	4,969		6,129		9,901	13,982
ASUS | Reportable Legal Entities | Contracted services:
Details of reportable segment
Total operating revenues	36,614		30,441		74,038	61,449
Supply costs	0		0		0	0
Other operation	2,688		2,431		5,471	5,005
Administrative and general	5,999		5,620		12,731	11,739
Depreciation and amortization	946		887		1,905	1,760
Maintenance	1,637		1,580		3,013	2,812
Property and other taxes	596		595		1,277	1,237
ASUS construction expense	16,747		12,890		34,080	25,823
Operating Income	8,001		6,438		15,561	13,073
Interest expense	(39)		(179)		(110)	(492)
Interest income	201		202		401	401
(Gain) loss on investments held in a trust	0		0		0	0
Income tax expense	1,984		1,599		3,873	2,976
Other segment items income (expense)	7		12		22	(8)
Net Income	6,186		4,874		12,001	9,998
Capital additions	552		1,566		2,427	3,420
Golden State Water Company and Bear Valley Electric Service Inc.
Details of reportable segment
Depreciation on transportation equipment	$ 300		$ 300		$ 600	$ 500