Utility Plant and Intangible Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Utility plant utilized in continuing operations by major asset class
Total amortized intangible assets	$ 31,192	$ 37,678
Total utility plant, at cost	1,674,527	1,620,325
Less - accumulated depreciation	(533,370)	(532,753)
Construction work in progress	(63,835)	(63,354)
Net utility plant	1,204,992	1,150,926	$ 1,060,794
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
Utility plant utilized in continuing operations by major asset class
Total utility plant, at cost	1,574,801	1,526,316
Water | Land
Utility plant utilized in continuing operations by major asset class
Total utility plant, at cost	14,895	15,393
Water | Intangible Assets [Member]
Utility plant utilized in continuing operations by major asset class
Total utility plant, at cost	29,396	36,291
Water | Source of water supply
Utility plant utilized in continuing operations by major asset class
Total utility plant, at cost	88,168	86,775
Water | Pumping
Utility plant utilized in continuing operations by major asset class
Total utility plant, at cost	178,252	169,983
Water | Water treatment
Utility plant utilized in continuing operations by major asset class
Total utility plant, at cost	78,999	74,980
Water | Transmission and distribution
Utility plant utilized in continuing operations by major asset class
Total utility plant, at cost	1,064,271	1,014,925
Water | General
Utility plant utilized in continuing operations by major asset class
Total utility plant, at cost	120,820	127,969
Electric
Utility plant utilized in continuing operations by major asset class
Total utility plant, at cost	99,726	94,009
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	76,188	71,112
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	10,955	10,314
GSWC
Utility plant utilized in continuing operations by major asset class
Total amortized intangible assets	30,621	37,107
Total utility plant, at cost	1,658,935	1,608,428
Less - accumulated depreciation	(524,481)	(524,927)
Construction work in progress	(63,486)	(61,810)
Net utility plant	1,197,940	1,145,311
GSWC | Water
Utility plant utilized in continuing operations by major asset class
Total utility plant, at cost	1,559,209	1,514,419
Net utility plant	1,137,995	1,089,031	1,005,114
GSWC | Water | Land
Utility plant utilized in continuing operations by major asset class
Total utility plant, at cost	14,895	15,393
GSWC | Water | Intangible Assets [Member]
Utility plant utilized in continuing operations by major asset class
Total utility plant, at cost	29,378	36,273
GSWC | Water | Source of water supply
Utility plant utilized in continuing operations by major asset class
Total utility plant, at cost	88,168	86,775
GSWC | Water | Pumping
Utility plant utilized in continuing operations by major asset class
Total utility plant, at cost	178,252	169,983
GSWC | Water | Water treatment
Utility plant utilized in continuing operations by major asset class
Total utility plant, at cost	78,999	74,980
GSWC | Water | Transmission and distribution
Utility plant utilized in continuing operations by major asset class
Total utility plant, at cost	1,064,271	1,014,925
GSWC | Water | General
Utility plant utilized in continuing operations by major asset class
Total utility plant, at cost	105,246	116,090
GSWC | Electric
Utility plant utilized in continuing operations by major asset class
Total utility plant, at cost	99,726	94,009
Net utility plant	59,945	56,280	$ 51,002
GSWC | Electric | Transmission and distribution
Utility plant utilized in continuing operations by major asset class
Total utility plant, at cost	76,188	71,112
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	10,955	10,314
Conservation [Member]
Utility plant utilized in continuing operations by major asset class
Total amortized intangible assets	9,486	9,496
Conservation [Member] | GSWC
Utility plant utilized in continuing operations by major asset class
Total amortized intangible assets	$ 9,486	$ 9,496