Business Segments: (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015 USD ($)	Jun. 30, 2014 USD ($)	Jun. 30, 2015 USD ($) segment	Jun. 30, 2014 USD ($)	Dec. 31, 2014 USD ($)
Details of reportable segment
Total operating revenues	$ 114,618	$ 115,641	$ 215,551	$ 217,586
Operating income (loss)	30,530	31,000	55,420	53,768
Interest expense, net	5,425	5,655	10,541	11,170
Utility plant	1,015,507	988,668	1,015,507	988,668	$ 1,003,520
Depreciation and amortization expense	10,536	10,525	21,084	21,055
Income tax expense (benefit)	9,534	10,262	17,432	16,619
Capital additions	16,817	15,089	$ 34,207	35,620
GSWC
Details of reportable segment
Number of reportable segments | segment			2
Total operating revenues	95,470	94,560	$ 177,943	175,773
Operating income (loss)	27,235	28,575	49,708	49,005
Utility plant	1,011,108		1,011,108		$ 998,880
Depreciation and amortization expense	10,235	10,232	20,476	20,472
Income tax expense (benefit)	8,800	9,783	16,047	15,488
Depreciation on transportation equipment	151	225	$ 374	497
AWR
Details of reportable segment
Number of reportable segments | segment			3
Reportable Legal Entities [Member] | GSWC | Water
Details of reportable segment
Total operating revenues	87,581	86,232	$ 159,085	156,989
Operating income (loss)	26,472	27,182	46,213	45,577
Interest expense, net	5,108	5,271	9,909	10,439
Utility plant	963,147	943,382	963,147	943,382
Depreciation and amortization expense	9,768	9,634	19,709	19,197
Income tax expense (benefit)	8,587	9,374	14,731	14,332
Capital additions	13,918	14,327	30,162	33,651
Reportable Legal Entities [Member] | GSWC | Electric
Details of reportable segment
Total operating revenues	7,889	8,328	18,858	18,784
Operating income (loss)	763	1,393	3,495	3,428
Interest expense, net	311	337	624	671
Utility plant	47,961	40,304	47,961	40,304
Depreciation and amortization expense	467	598	767	1,275
Income tax expense (benefit)	213	409	1,316	1,156
Capital additions	2,605	208	3,679	680
Reportable Legal Entities [Member] | ASUS | Contracts
Details of reportable segment
Total operating revenues	19,148	21,081	37,608	41,813
Operating income (loss)	3,297	2,425	5,717	4,809
Interest expense, net	8	55	16	122
Utility plant	4,399	4,982	4,399	4,982
Depreciation and amortization expense	301	293	608	583
Income tax expense (benefit)	888	923	1,759	1,746
Capital additions	294	554	366	1,289
Intersegment Eliminations | AWR
Details of reportable segment
Total operating revenues	0	0	0	0
Operating income (loss)	(2)	0	(5)	(46)
Interest expense, net	(2)	(8)	(8)	(62)
Utility plant	0	0	0	0
Depreciation and amortization expense	0	0	0	0
Income tax expense (benefit)	(154)	(444)	(374)	(615)
Capital additions	$ 0	$ 0	$ 0	$ 0