Utility Plant and Intangible Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Utility plant utilized in continuing operations by major asset class
Total amortized intangible assets	$ 29,989	$ 30,822
Total utility plant, at cost	1,839,421	1,780,110
Less - accumulated depreciation	(543,263)	(561,855)
Construction work in progress	(119,547)	(78,055)
Net utility plant	1,415,705	1,296,310	$ 1,204,992
American States Utility Services [Member] | Intangible Assets [Member]
Utility plant utilized in continuing operations by major asset class
Total utility plant, at cost	571	571
Water Service Utility Operations [Member]
Utility plant utilized in continuing operations by major asset class
Total utility plant, at cost	1,730,996	1,674,046
Water Service Utility Operations [Member] | Land
Utility plant utilized in continuing operations by major asset class
Total utility plant, at cost	18,066	14,890
Water Service Utility Operations [Member] | Intangible Assets [Member]
Utility plant utilized in continuing operations by major asset class
Total utility plant, at cost	28,578	29,412
Water Service Utility Operations [Member] | Source of water supply
Utility plant utilized in continuing operations by major asset class
Total utility plant, at cost	91,685	91,349
Water Service Utility Operations [Member] | Pumping
Utility plant utilized in continuing operations by major asset class
Total utility plant, at cost	178,058	182,673
Water Service Utility Operations [Member] | Water treatment
Utility plant utilized in continuing operations by major asset class
Total utility plant, at cost	78,048	82,198
Water Service Utility Operations [Member] | Transmission and distribution
Utility plant utilized in continuing operations by major asset class
Total utility plant, at cost	1,219,285	1,142,105
Water Service Utility Operations [Member] | General
Utility plant utilized in continuing operations by major asset class
Total utility plant, at cost	117,276	131,419
Electric:
Utility plant utilized in continuing operations by major asset class
Total utility plant, at cost	108,425	106,064
Electric: | Intangible Assets [Member]
Utility plant utilized in continuing operations by major asset class
Total utility plant, at cost	1,200	1,200
Electric: | Transmission and distribution
Utility plant utilized in continuing operations by major asset class
Total utility plant, at cost	84,018	82,257
Electric: | Generation
Utility plant utilized in continuing operations by major asset class
Total utility plant, at cost	12,583	12,583
Electric: | General
Utility plant utilized in continuing operations by major asset class
Total utility plant, at cost	11,824	11,224
GSWC
Utility plant utilized in continuing operations by major asset class
Total amortized intangible assets	29,418	30,251
Total utility plant, at cost	1,808,867	1,755,599
Less - accumulated depreciation	(531,801)	(551,244)
Construction work in progress	(117,676)	(76,737)
Net utility plant	1,394,742	1,281,092
GSWC | Water Service Utility Operations [Member]
Utility plant utilized in continuing operations by major asset class
Total utility plant, at cost	1,700,442	1,649,535
Net utility plant	1,322,062	1,218,468	1,137,995
GSWC | Water Service Utility Operations [Member] | Land
Utility plant utilized in continuing operations by major asset class
Total utility plant, at cost	18,066	14,890
GSWC | Water Service Utility Operations [Member] | Intangible Assets [Member]
Utility plant utilized in continuing operations by major asset class
Total utility plant, at cost	28,578	29,413
GSWC | Water Service Utility Operations [Member] | Source of water supply
Utility plant utilized in continuing operations by major asset class
Total utility plant, at cost	91,685	91,349
GSWC | Water Service Utility Operations [Member] | Pumping
Utility plant utilized in continuing operations by major asset class
Total utility plant, at cost	178,058	182,673
GSWC | Water Service Utility Operations [Member] | Water treatment
Utility plant utilized in continuing operations by major asset class
Total utility plant, at cost	78,048	82,198
GSWC | Water Service Utility Operations [Member] | Transmission and distribution
Utility plant utilized in continuing operations by major asset class
Total utility plant, at cost	1,219,285	1,142,105
GSWC | Water Service Utility Operations [Member] | General
Utility plant utilized in continuing operations by major asset class
Total utility plant, at cost	86,722	106,907
GSWC | Electric:
Utility plant utilized in continuing operations by major asset class
Total utility plant, at cost	108,425	106,064
Net utility plant	72,680	62,624	$ 59,945
GSWC | Electric: | Transmission and distribution
Utility plant utilized in continuing operations by major asset class
Total utility plant, at cost	84,018	82,257
GSWC | Electric: | Generation
Utility plant utilized in continuing operations by major asset class
Total utility plant, at cost	12,583	12,583
GSWC | Electric: | General
Utility plant utilized in continuing operations by major asset class
Total utility plant, at cost	11,824	11,224
Conservation [Member]
Utility plant utilized in continuing operations by major asset class
Total amortized intangible assets	9,486	9,486
Conservation [Member] | GSWC
Utility plant utilized in continuing operations by major asset class
Total amortized intangible assets	$ 9,486	$ 9,486