Business Segments: (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($) segment	Jun. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)
Details of reportable segment
Total operating revenues	$ 106,901	$ 113,195	$ 201,629	$ 212,005
Operating income (loss)	25,568	42,026	44,259	66,602
Interest expense, net	5,412	5,306	10,799	10,952
Utility plant	1,238,789	1,155,203	1,238,789	1,155,203	$ 1,204,992
Depreciation and amortization expense	10,010	9,647	19,676	19,330
Income tax expense (benefit)	4,387	14,307	6,951	21,162
Capital additions	28,418	21,902	$ 58,782	45,896
AWR
Details of reportable segment
Number of reportable segments | segment			3
Golden State Water Company [Member]
Details of reportable segment
Number of reportable segments | segment			2
Total operating revenues	84,574	88,346	$ 158,818	165,252
Operating income (loss)	22,645	35,229	38,942	57,105
Utility plant	1,227,371		1,227,371		$ 1,197,940
Depreciation and amortization expense	9,430	9,394	18,764	18,832
Income tax expense (benefit)	4,214	12,149	6,329	18,422
Reportable Legal Entities | Golden State Water Company [Member] | Water Service Utility Operations
Details of reportable segment
Total operating revenues	76,733	80,734	141,145	147,138
Operating income (loss)	21,244	33,695	35,302	52,792
Interest expense, net	5,047	4,805	10,056	9,950
Utility plant	1,166,867	1,093,104	1,166,867	1,093,104
Depreciation and amortization expense	8,866	8,858	17,635	17,759
Income tax expense (benefit)	3,909	11,710	5,558	17,195
Capital additions	24,768	20,593	51,386	43,577
Reportable Legal Entities | Golden State Water Company [Member] | Electric
Details of reportable segment
Total operating revenues	7,841	7,612	17,673	18,114
Operating income (loss)	1,401	1,534	3,640	4,313
Interest expense, net	353	350	723	725
Utility plant	60,504	56,371	60,504	56,371
Depreciation and amortization expense	564	536	1,129	1,073
Income tax expense (benefit)	305	439	771	1,227
Capital additions	1,150	978	2,124	1,701
Reportable Legal Entities | American States Utility Services [Member] | Contracted Services [Member]
Details of reportable segment
Total operating revenues	22,327	24,849	42,811	46,753
Operating income (loss)	2,925	6,800	5,322	9,504
Interest expense, net	(71)	82	(137)	156
Utility plant	11,418	5,728	11,418	5,728
Depreciation and amortization expense	580	253	912	498
Income tax expense (benefit)	705	2,347	1,259	3,208
Capital additions	2,500	331	5,272	618
Intersegment Eliminations | AWR
Details of reportable segment
Total operating revenues	0	0	0	0
Operating income (loss)	(2)	(3)	(5)	(7)
Interest expense, net	83	69	157	121
Utility plant	0	0	0	0
Depreciation and amortization expense	0	0	0	0
Income tax expense (benefit)	(532)	(189)	(637)	(468)
Capital additions	$ 0	$ 0	$ 0	$ 0