STATEMENTS OF CHANGES IN COMMON SHAREHOLDER'S EQUITY - USD ($) $ in Thousands	Total	Common Stock Including Additional Paid in Capital	Retained Earnings	GOLDEN STATE WATER COMPANY	GOLDEN STATE WATER COMPANY Common Stock Including Additional Paid in Capital	GOLDEN STATE WATER COMPANY Retained Earnings
Beginning Balance (in shares) at Dec. 31, 2023		36,981,000			171.0000
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 offering 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			171.0000
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			171.0000
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			171.0000
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			171.0000
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 offering 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			171.0000
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 offering 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			171.0000
Ending balances at Sep. 30, 2024	879,466	$ 325,278	554,188	763,350	$ 373,548	389,802
Beginning Balance (in shares) at Dec. 31, 2024		38,151,000			173.7586
Beginning balances at Dec. 31, 2024	920,051	$ 355,143	564,908	805,833	$ 413,797	392,036
Add:
Net income	26,844		26,844	19,906		19,906
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 offering program, net of issuance costs	25,648	$ 25,648
Issuances of Common Shares under stock-based compensation plans (in shares)		23,000
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)	1,626	1,626		1,634	1,634
Dividend equivalent rights on stock-based awards not paid in cash	63	$ 63		57	$ 57
Deduct:
Dividends on Common Shares	17,762		17,762
Dividend equivalent rights on stock-based awards not paid in cash	63		63	57		57
Ending Balances (in shares) at Mar. 31, 2025		38,509,000			173.7586
Ending balances at Mar. 31, 2025	956,407	$ 382,480	573,927	827,373	$ 415,488	411,885
Beginning Balance (in shares) at Dec. 31, 2024		38,151,000			173.7586
Beginning balances at Dec. 31, 2024	920,051	$ 355,143	564,908	805,833	$ 413,797	392,036
Add:
Net income	$ 101,701			$ 81,344
Issuance of Common Shares from an at-the-market program, net of issuance costs (in shares)				3.6500
Issuance of Common Shares from an at-the-market offering program, net of issuance costs				$ 50,000
Issuances of Common Shares under stock-based compensation plans (in shares)	27,639
Ending Balances (in shares) at Sep. 30, 2025		38,714,000			177.4086
Ending balances at Sep. 30, 2025	$ 1,009,309	$ 398,010	611,299	901,926	$ 466,239	435,687
Beginning Balance (in shares) at Mar. 31, 2025		38,509,000			173.7586
Beginning balances at Mar. 31, 2025	956,407	$ 382,480	573,927	827,373	$ 415,488	411,885
Add:
Net income	33,690		33,690	28,140		28,140
Issuance of Common Shares from an at-the-market program, net of issuance costs (in shares)					3.6500
Issuance of Common Shares from an at-the-market offering program, net of issuance costs				50,005	$ 50,005
Issuance costs from an at-the-market offering program	(78)	(78)
Stock-based compensation, net of taxes paid from shares withheld from employees related to net share settlements (Note 4)	426	426		318	318
Dividend equivalent rights on stock-based awards not paid in cash	72	$ 72		64	$ 64
Deduct:
Dividends on Common Shares	17,926		17,926	18,000		18,000
Dividend equivalent rights on stock-based awards not paid in cash	72		72	64		64
Ending Balances (in shares) at Jun. 30, 2025		38,509,000			177.4086
Ending balances at Jun. 30, 2025	972,519	$ 382,900	589,619	887,836	$ 465,875	421,961
Add:
Net income	41,167		41,167	33,298		33,298
Issuance of Common Shares from an at-the-market program, net of issuance costs (in shares)		201,000
Issuance of Common Shares from an at-the-market offering program, net of issuance costs	14,624	$ 14,624
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)	407	407		292	292
Dividend equivalent rights on stock-based awards not paid in cash	79	$ 79		72	$ 72
Deduct:
Dividends on Common Shares	19,408		19,408	19,500		19,500
Dividend equivalent rights on stock-based awards not paid in cash	79		79	72		72
Ending Balances (in shares) at Sep. 30, 2025		38,714,000			177.4086
Ending balances at Sep. 30, 2025	$ 1,009,309	$ 398,010	$ 611,299	$ 901,926	$ 466,239	$ 435,687