Business Segments: (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($) segment	Sep. 30, 2014 USD ($)	Dec. 31, 2014 USD ($)
Details of reportable segment
Total operating revenues	$ 132,975	$ 138,327	$ 348,526	$ 355,913
Operating income (loss)	41,185	39,895	96,605	93,663
Interest expense, net	5,366	5,295	15,907	16,465
Utility plant	1,032,119	995,443	1,032,119	995,443	$ 1,003,520
Depreciation and amortization expense	10,512	10,549	31,596	31,604
Income tax expense (benefit)	14,394	13,476	31,826	30,095
Capital additions	25,641	18,094	$ 59,848	53,714
GSWC
Details of reportable segment
Number of reportable segments | segment			2
Total operating revenues	105,219	105,314	$ 283,162	281,087
Operating income (loss)	34,081	32,346	83,789	81,351
Utility plant	1,027,843		1,027,843		$ 998,880
Depreciation and amortization expense	10,241	10,236	30,717	30,708
Income tax expense (benefit)	12,109	11,019	28,156	26,507
Depreciation on transportation equipment	140	201	$ 514	698
AWR
Details of reportable segment
Number of reportable segments | segment			3
Reportable Legal Entities [Member] | GSWC | Water
Details of reportable segment
Total operating revenues	97,273	96,700	$ 256,358	253,689
Operating income (loss)	33,178	31,185	79,391	76,762
Interest expense, net	5,117	4,976	15,026	15,415
Utility plant	977,549	950,256	977,549	950,256
Depreciation and amortization expense	9,773	9,643	29,482	28,840
Income tax expense (benefit)	11,819	10,749	26,550	25,081
Capital additions	22,608	17,093	52,770	50,744
Reportable Legal Entities [Member] | GSWC | Electric
Details of reportable segment
Total operating revenues	7,946	8,614	26,804	27,398
Operating income (loss)	903	1,161	4,398	4,589
Interest expense, net	267	319	891	990
Utility plant	50,294	40,333	50,294	40,333
Depreciation and amortization expense	468	593	1,235	1,868
Income tax expense (benefit)	290	270	1,606	1,426
Capital additions	2,881	726	6,560	1,406
Reportable Legal Entities [Member] | ASUS | Contracts
Details of reportable segment
Total operating revenues	27,756	33,013	65,364	74,826
Operating income (loss)	7,108	7,549	12,825	12,358
Interest expense, net	7	10	23	132
Utility plant	4,276	4,854	4,276	4,854
Depreciation and amortization expense	271	313	879	896
Income tax expense (benefit)	2,590	2,857	4,349	4,603
Capital additions	152	275	518	1,564
Intersegment Eliminations | AWR
Details of reportable segment
Total operating revenues	0	0	0	0
Operating income (loss)	(4)	0	(9)	(46)
Interest expense, net	(25)	(10)	(33)	(72)
Utility plant	0	0	0	0
Depreciation and amortization expense	0	0	0	0
Income tax expense (benefit)	(305)	(400)	(679)	(1,015)
Capital additions	$ 0	$ 0	$ 0	$ 0