Business Segments: (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) segment	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Details of reportable segment
Total operating revenues	$ 133,688	$ 134,496	$ 364,043	$ 360,876
Operating income (loss)	39,807	42,724	101,222	102,349
Interest expense, net	5,845	5,453	16,169	16,234
Net property, plant and equipment	1,479,110	1,378,366	1,479,110	1,378,366	$ 1,415,705
Depreciation and amortization expense	9,348	9,006	27,190	26,493
Income tax expense (benefit)	9,045	9,405	21,227	20,546
Capital additions	32,237	29,933	$ 94,824	111,088
AWR
Details of reportable segment
Number of reportable segments | segment			3
GOLDEN STATE WATER COMPANY
Details of reportable segment
Public Utilities Property Plant and Equipment Depreciation on Transportation Equipment	84	80	$ 249	234
Number of reportable segments | segment			2
Total operating revenues	98,701	107,245	$ 275,846	278,145
Operating income (loss)	33,149	36,982	85,416	86,346
Net property, plant and equipment	1,373,323		1,373,323		$ 1,394,742
Depreciation and amortization expense	7,835	8,359	24,073	24,354
Income tax expense (benefit)	7,683	8,383	18,220	17,329
GOLDEN STATE WATER COMPANY | Water Service Utility Operations
Details of reportable segment
Total operating revenues	98,701	95,249	$ 257,199	248,112
GOLDEN STATE WATER COMPANY | Electric Service Utility Operations
Details of reportable segment
Total operating revenues		11,996		30,033
ASUS | Contracted Services
Details of reportable segment
Period of fixed price contracts to operate and maintain water systems at various military bases			50 years
Bear Valley Electric Service, Inc. | Electric Service Utility Operations
Details of reportable segment
Total operating revenues	8,288
Golden State Water Company and Bear Valley Electric Service Inc. | Electric Service Utility Operations
Details of reportable segment
Total operating revenues			$ 26,935
Reportable Legal Entities | GOLDEN STATE WATER COMPANY | Water Service Utility Operations
Details of reportable segment
Total operating revenues	98,701	95,249	257,199	248,112
Operating income (loss)	33,149	31,310	80,416	77,835
Interest expense, net	5,806	5,206	15,796	15,555
Net property, plant and equipment	1,373,323	1,291,928	1,373,323	1,291,928
Depreciation and amortization expense	7,835	7,690	22,858	22,484
Income tax expense (benefit)	7,683	6,720	17,031	15,205
Capital additions	28,076	25,267	78,611	99,939
Reportable Legal Entities | GOLDEN STATE WATER COMPANY | Electric Service Utility Operations
Details of reportable segment
Total operating revenues		11,996		30,033
Operating income (loss)		5,672		8,511
Interest expense, net		234		933
Net property, plant and equipment		66,902		66,902
Depreciation and amortization expense		669		1,870
Income tax expense (benefit)		1,663		2,124
Capital additions		2,864		4,852
Reportable Legal Entities | ASUS | Contracted Services
Details of reportable segment
Total operating revenues	26,699	27,251	79,909	82,731
Operating income (loss)	4,794	5,745	13,946	16,010
Interest expense, net	(74)	144	(371)	724
Net property, plant and equipment	22,599	19,536	22,599	19,536
Depreciation and amortization expense	887	647	2,491	2,139
Income tax expense (benefit)	1,150	1,391	3,199	3,816
Capital additions	1,122	1,802	4,120	6,297
Reportable Legal Entities | Bear Valley Electric Service, Inc. | Electric Service Utility Operations
Details of reportable segment
Total operating revenues	8,288
Operating income (loss)	1,865
Interest expense, net	54
Net property, plant and equipment	83,188		83,188
Depreciation and amortization expense	626
Income tax expense (benefit)	533
Capital additions	3,039
Reportable Legal Entities | Golden State Water Company and Bear Valley Electric Service Inc. | Electric Service Utility Operations
Details of reportable segment
Total operating revenues			26,935
Operating income (loss)			6,865
Interest expense, net			519
Depreciation and amortization expense			1,841
Income tax expense (benefit)			1,722
Capital additions			12,093
Intersegment Eliminations | AWR
Details of reportable segment
Total operating revenues	0	0	0	0
Operating income (loss)	(1)	(3)	(5)	(7)
Interest expense, net	(59)	(157)	225	(470)
Net property, plant and equipment	0	0	0	0
Depreciation and amortization expense	0	0	0	0
Income tax expense (benefit)	(321)	(369)	(725)	(599)
Capital additions	$ 0	$ 0	$ 0	$ 0