STATEMENTS OF CHANGES IN COMMON SHAREHOLDER'S EQUITY - USD ($) $ in Thousands	Total	Common Shares	Retained Earnings	GOLDEN STATE WATER COMPANY	GOLDEN STATE WATER COMPANY Common Shares	GOLDEN STATE WATER COMPANY Retained Earnings
Beginning Balance (in shares) at Dec. 31, 2022		36,962,000			170
Beginning balances at Dec. 31, 2022	$ 709,549	$ 260,158	$ 449,391	$ 643,906	$ 358,123	$ 285,783
Add:
Net income	34,407		34,407	27,463		27,463
Issuance of Common Shares from an at-the-market program, net of issuance costs (in shares)					1
Issuance of Common Shares from an at-the-market program, net of issuance costs				10,000	$ 10,000
Issuances of Common Shares under stock-based compensation plans (in shares)		14,000
Issuances of Common Shares under stock-based compensation plans	0	$ 0
Stock-based compensation, net of taxes paid from shares withheld from employees related to net share settlements (Note 4)	1,587	1,587		1,603	1,603
Dividend equivalent rights on stock-based awards not paid in cash	47	$ 47		44	$ 44
Deduct:
Dividends on Common Shares	14,695		14,695	24,700		24,700
Dividend equivalent rights on stock-based awards not paid in cash	47		47	44		44
Ending Balances (in shares) at Mar. 31, 2023		36,976,000			171
Ending balances at Mar. 31, 2023	730,848	$ 261,792	469,056	658,272	$ 369,770	288,502
Beginning Balance (in shares) at Dec. 31, 2022		36,962,000			170
Beginning balances at Dec. 31, 2022	709,549	$ 260,158	449,391	643,906	$ 358,123	285,783
Add:
Net income	$ 104,493			$ 87,589
Issuance of Common Shares from an at-the-market program, net of issuance costs (in shares)				1
Issuance of Common Shares from an at-the-market program, net of issuance costs				$ 10,000
Issuances of Common Shares under stock-based compensation plans (in shares)	18,351
Deduct:
Dividend equivalent rights on stock-based awards not paid in cash						39
Ending Balances (in shares) at Sep. 30, 2023		36,981,000			171
Ending balances at Sep. 30, 2023	$ 771,337	$ 262,884	508,453	688,525	$ 370,680	317,845
Beginning Balance (in shares) at Mar. 31, 2023		36,976,000			171
Beginning balances at Mar. 31, 2023	730,848	$ 261,792	469,056	658,272	$ 369,770	288,502
Add:
Net income	38,521		38,521	33,533		33,533
Issuances of Common Shares under stock-based compensation plans (in shares)		1,000
Issuances of Common Shares under stock-based compensation plans	0	$ 0
Stock-based compensation, net of taxes paid from shares withheld from employees related to net share settlements (Note 4)	396	396		320	320
Dividend equivalent rights on stock-based awards not paid in cash	42	$ 42		39	$ 39
Deduct:
Dividends on Common Shares	14,699		14,699	14,700		14,700
Dividend equivalent rights on stock-based awards not paid in cash	42		42	39
Ending Balances (in shares) at Jun. 30, 2023		36,977,000			171
Ending balances at Jun. 30, 2023	755,066	$ 262,230	492,836	677,425	$ 370,129	307,296
Add:
Net income	31,565		31,565	$ 26,593		26,593
Issuance of Common Shares from an at-the-market program, net of issuance costs (in shares)				1
Issuance of Common Shares from an at-the-market program, net of issuance costs				$ 10,000
Issuances of Common Shares under stock-based compensation plans (in shares)		4,000
Issuances of Common Shares under stock-based compensation plans	0	$ 0
Stock-based compensation, net of taxes paid from shares withheld from employees related to net share settlements (Note 4)	606	606		507	507
Dividend equivalent rights on stock-based awards not paid in cash	48	$ 48		44	$ 44
Deduct:
Dividends on Common Shares	15,900		15,900			16,000
Dividend equivalent rights on stock-based awards not paid in cash	48		48			44
Ending Balances (in shares) at Sep. 30, 2023		36,981,000			171
Ending balances at Sep. 30, 2023	771,337	$ 262,884	508,453	688,525	$ 370,680	317,845
Beginning Balance (in shares) at Dec. 31, 2023		36,981,000			171
Beginning balances at Dec. 31, 2023	776,109	$ 263,179	512,930	703,828	$ 370,909	332,919
Add:
Net income	23,135		23,135	17,794		17,794
Issuance of Common Shares from an at-the-market program, net of issuance costs (in shares)		228,000
Issuance of Common Shares from an at-the-market program, net of issuance costs	15,584	$ 15,584
Issuances of Common Shares under stock-based compensation plans (in shares)		20,000
Issuances of Common Shares under stock-based compensation plans	0	$ 0
Stock-based compensation, net of taxes paid from shares withheld from employees related to net share settlements (Note 4)	1,570	1,570		1,561	1,561
Dividend equivalent rights on stock-based awards not paid in cash	44	$ 44		41	$ 41
Deduct:
Dividends on Common Shares	15,905		15,905
Dividend equivalent rights on stock-based awards not paid in cash	44		44	41		41
Ending Balances (in shares) at Mar. 31, 2024		37,229,000			171
Ending balances at Mar. 31, 2024	800,493	$ 280,377	520,116	723,183	$ 372,511	350,672
Beginning Balance (in shares) at Dec. 31, 2023		36,981,000			171
Beginning balances at Dec. 31, 2023	776,109	$ 263,179	512,930	703,828	$ 370,909	332,919
Add:
Net income	$ 90,833			74,555
Issuances of Common Shares under stock-based compensation plans (in shares)	25,164
Ending Balances (in shares) at Sep. 30, 2024		37,797,000			171
Ending balances at Sep. 30, 2024	$ 879,466	$ 325,278	554,188	763,350	$ 373,548	389,802
Beginning Balance (in shares) at Mar. 31, 2024		37,229,000			171
Beginning balances at Mar. 31, 2024	800,493	$ 280,377	520,116	723,183	$ 372,511	350,672
Add:
Net income	31,864		31,864	25,195		25,195
Issuance of Common Shares from an at-the-market program, net of issuance costs (in shares)		228,000
Issuance of Common Shares from an at-the-market program, net of issuance costs	16,724	$ 16,724
Stock-based compensation, net of taxes paid from shares withheld from employees related to net share settlements (Note 4)	420	420		331	331
Dividend equivalent rights on stock-based awards not paid in cash	55	$ 55		50	$ 50
Deduct:
Dividends on Common Shares	16,024		16,024
Dividend equivalent rights on stock-based awards not paid in cash	55		55	50		50
Ending Balances (in shares) at Jun. 30, 2024		37,457,000			171
Ending balances at Jun. 30, 2024	833,477	$ 297,576	535,901	748,709	$ 372,892	375,817
Add:
Net income	35,834		35,834	31,566		31,566
Issuance of Common Shares from an at-the-market program, net of issuance costs (in shares)		335,000
Issuance of Common Shares from an at-the-market program, net of issuance costs	26,881	$ 26,881
Issuances of Common Shares under stock-based compensation plans (in shares)		5,000
Issuances of Common Shares under stock-based compensation plans	0	$ 0
Stock-based compensation, net of taxes paid from shares withheld from employees related to net share settlements (Note 4)	729	729		575	575
Dividend equivalent rights on stock-based awards not paid in cash	92	$ 92		81	$ 81
Deduct:
Dividends on Common Shares	17,455		17,455	17,500		17,500
Dividend equivalent rights on stock-based awards not paid in cash	92		92	81		81
Ending Balances (in shares) at Sep. 30, 2024		37,797,000			171
Ending balances at Sep. 30, 2024	$ 879,466	$ 325,278	$ 554,188	$ 763,350	$ 373,548	$ 389,802