Business Segments (Details) $ in Thousands		3 Months Ended								12 Months Ended
		Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2017 USD ($) segment	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Details of reportable segment
Operating revenues		$ 104,180	$ 124,418	$ 113,195	$ 98,810	$ 106,800	$ 123,806	$ 111,954	$ 93,527	$ 440,603	$ 436,087	$ 458,641
Operating income (loss)		21,955	38,567	41,816	24,738	22,092	39,617	31,774	21,233	127,076	114,716	118,489
Interest expense, net										(20,792)	(21,235)	(20,630)
Net utility plant		1,204,992				1,150,926				1,204,992	1,150,926	1,060,794
Depreciation and amortization expense	[1]									39,031	38,850	42,033
Income tax expense/(benefit)										38,974	34,735	37,731
Capital additions										$ 113,126	129,867	87,323
AWR Parent
Details of reportable segment
Number of reportable segments | segment										3
Operating revenues										$ 0	0	0
Operating income (loss)										(96)	(19)	(11)
Interest expense, net										(248)	(134)	(46)
Net utility plant		0				0				0	0	0
Depreciation and amortization expense	[1]									0	0	0
Income tax expense/(benefit)											(546)	(810)
Capital additions										$ 0	0	0
GSWC
Details of reportable segment
Number of reportable segments | segment										2
Operating revenues		75,136	99,913	88,346	76,906	74,295	98,763	88,759	76,885	$ 340,301	338,702	364,550
Operating income (loss)		15,824	$ 33,068	$ 35,079	$ 22,077	14,477	$ 34,142	$ 27,557	$ 19,643	106,048	95,819	100,409
Net utility plant		1,197,940				1,145,311				1,197,940	1,145,311
Depreciation and amortization expense										37,852	37,804	40,893
Income tax expense/(benefit)										34,059	28,609	32,472
GSWC | Water
Details of reportable segment
Operating revenues										306,332	302,931	328,511
Operating income (loss)										98,797	87,911	94,213
Interest expense, net										(18,909)	(19,696)	(19,468)
Net utility plant		1,137,995				1,089,031				1,137,995	1,089,031	1,005,114
Depreciation and amortization expense	[1]									35,706	35,777	39,190
Income tax expense/(benefit)										32,212	25,894	30,302
Capital additions										104,546	120,850	77,440
GSWC | Electric
Details of reportable segment
Operating revenues										33,969	35,771	36,039
Operating income (loss)										7,251	7,908	6,196
Interest expense, net										(1,380)	(1,337)	(1,090)
Net utility plant		59,945				56,280				59,945	56,280	51,002
Depreciation and amortization expense	[1]									2,146	2,027	1,703
Income tax expense/(benefit)										1,847	2,715	2,170
Capital additions										5,941	7,063	8,704
American States Utility Services [Member] | Military Utility Privatization Subsidiaries
Details of reportable segment
Operating revenues										100,302	97,385	94,091
Operating income (loss)										21,124	18,916	18,091
Interest expense, net										(255)	(68)	(26)
Net utility plant		$ 7,052				$ 5,615				7,052	5,615	4,678
Depreciation and amortization expense	[1]									1,179	1,046	1,140
Income tax expense/(benefit)										7,136	6,672	6,069
Capital additions										$ 2,639	$ 1,954	$ 1,179

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