Business Segments: (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Details of reportable segment
Operating revenues	$ 110,552	$ 106,892
Operating income (loss)	27,963	23,367
Interest expense, net	5,591	5,855
Utility Plant	929,538	897,835	917,791
Depreciation and amortization expense	9,816	10,490
Income tax expense	9,249	7,626
Capital additions	18,425	14,967
GSWC
Details of reportable segment
Number of reportable segments	2
Operating revenues	79,967	77,014
Operating income (loss)	23,596	18,707
Utility Plant	924,826		913,137
Depreciation and amortization expense	9,522	10,220
Income tax expense	7,663	5,755
GSWC | Water
Details of reportable segment
Operating revenues	69,233	66,201
Operating income (loss)	21,763	14,851
Interest expense, net	5,194	5,406
Utility Plant	883,863	853,533
Depreciation and amortization expense	8,930	9,597
Income tax expense	6,941	4,355
Capital additions	17,878	13,940
GSWC | Electric
Details of reportable segment
Operating revenues	10,734	10,813
Operating income (loss)	1,833	3,856
Interest expense, net	376	393
Utility Plant	40,963	39,526
Depreciation and amortization expense	592	623
Income tax expense	722	1,400
Capital additions	233	539
ASUS | Contracts
Details of reportable segment
Operating revenues	30,585	29,878
Operating income (loss)	4,367	4,741
Interest expense, net	60	54
Utility Plant	4,712	4,776
Depreciation and amortization expense	294	270
Income tax expense	1,666	1,829
Capital additions	314	488
AWR Parent
Details of reportable segment
Number of principal business units	3
Operating income (loss)		(81)
Interest expense, net	(39)	2
Income tax expense	$ (80)	$ 42