CONSOLIDATED STATEMENTS OF CHANGES IN COMMON SHAREHOLDERS' EQUITY - USD ($) $ in Thousands	Total	GSWC	Common Stock Including Additional Paid in Capital	Common Stock Including Additional Paid in Capital GSWC	Retained Earnings	Retained Earnings GSWC
Beginning Balance (in shares) at Dec. 31, 2022			36,962,000	170.0000
Beginning Balance at Dec. 31, 2022	$ 709,549	$ 643,906	$ 260,158	$ 358,123	$ 449,391	$ 285,783
Add:
Net Income	$ 124,921	$ 102,708			124,921	102,708
Issuance of Common Shares from an at-the-market program, net of issuance costs (in Shares)	18,371	1		1.0000
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)			19,000
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	2,834	2,614	2,834	2,614
Dividend equivalent rights on stock-based awards not paid in cash	187	172	$ 187	$ 172
Deduct:
Dividends on Common Shares	61,195	55,400			61,195	55,400
Dividend equivalent rights on stock-based awards	187	172			187	172
Ending Balance (in shares) at Dec. 31, 2023			36,981,000	171.0000
Ending Balance at Dec. 31, 2023	776,109	703,828	$ 263,179	$ 370,909	512,930	332,919
Add:
Net Income	$ 119,268	$ 94,463			119,268	94,463
Issuance of Common Shares from an at-the-market program, net of issuance costs (in Shares)	25,196	2.7586	1,145,000	2.7586
Issuance of Common Shares from an at-the-market program, net of issuance costs	$ 88,661	$ 40,000	$ 88,661	$ 40,000
Issuances of Common Shares under stock-based compensation plans ( in shares)			25,000
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	3,030	2,642	3,030	2,642
Dividend equivalent rights on stock-based awards not paid in cash	273	246	$ 273	$ 246
Deduct:
Dividends on Common Shares	67,017	35,100			67,017	35,100
Dividend equivalent rights on stock-based awards	$ 273	$ 246			273	246
Ending Balance (in shares) at Dec. 31, 2024	38,151,027	173.7586	38,151,000	173.7586
Ending Balance at Dec. 31, 2024	$ 920,051	$ 805,833	$ 355,143	$ 413,797	564,908	392,036
Add:
Net Income	$ 130,442	$ 100,946			130,442	100,946
Issuance of Common Shares from an at-the-market program, net of issuance costs (in Shares)	27,674	4.6250	904,000	4.6250
Issuance of Common Shares from an at-the-market program, net of issuance costs	$ 66,998	$ 61,998	$ 66,998	$ 61,998
Issuances of Common Shares under stock-based compensation plans ( in shares)			27,000
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	2,748	2,460	2,748	2,460
Dividend equivalent rights on stock-based awards not paid in cash	264	239	$ 264	$ 239
Deduct:
Dividends on Common Shares	74,658	37,500			74,658	37,500
Dividend equivalent rights on stock-based awards	$ 264	$ 239			264	239
Ending Balance (in shares) at Dec. 31, 2025	39,082,470	178.3836	39,082,000	178.3836
Ending Balance at Dec. 31, 2025	$ 1,045,581	$ 933,737	$ 425,153	$ 478,494	$ 620,428	$ 455,243