Selected Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								6 Months Ended	12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating revenues	$ 112,993	$ 134,496	$ 124,647	$ 101,733	$ 111,005	$ 124,182	$ 106,901	$ 94,728		$ 473,869	$ 436,816	$ 440,603
Net Income	$ 16,700	$ 28,006	$ 26,784	$ 12,852	$ 13,789	$ 22,952	$ 16,348	$ 10,782		$ 84,342	$ 63,871	$ 69,367
Earnings Per Share, Basic	$ 0.45	$ 0.76	$ 0.72	$ 0.35	$ 0.37	$ 0.62	$ 0.44	$ 0.29		$ 2.28	$ 1.73	$ 1.88
Earnings Per Share, Diluted	$ 0.45	$ 0.76	$ 0.72	$ 0.35	$ 0.37	$ 0.62	$ 0.44	$ 0.29		$ 2.28	$ 1.72	$ 1.88
GSWC
Operating revenues	$ 81,233	$ 107,245	$ 95,548	$ 75,352	$ 75,226	$ 95,564	$ 84,574	$ 74,244		$ 359,378	$ 329,608	$ 340,301
Net Income	$ 11,981	$ 23,362	$ 22,298	9,022	$ 7,555	$ 17,919	$ 13,648	$ 8,890		66,663	48,012	53,757
Water Service Utility Operations [Member] | GSWC
Operating revenues										319,830	295,258	306,332
Retroactive pretax income adjustment due to GRC delay				$ 4,000
Electric: | GSWC
Operating revenues										$ 39,548	34,350	$ 33,969
Retroactive pretax income adjustment due to GRC delay									$ 1,400		$ 2,300