Business Segments (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Details of reportable segment
Operating revenues	$ 466,908,000	$ 419,913,000	$ 399,776,000
Operating income (loss)	111,094,000	95,104,000	73,819,000
Interest expense, net	21,432,000	22,822,000	19,230,000
Utility Plant	917,791,000	896,500,000	854,956,000
Depreciation and amortization expense	41,385,000	38,349,000	37,405,000
Income tax expense/(benefit)	35,945,000	30,076,000	23,035,000
Income (loss) from discontinued operations		3,849,000	2,106,000
Capital additions	68,104,000	80,281,000	79,050,000
Contracts
Details of reportable segment
Operating income (loss)	24,608,000	11,855,000
GSWC
Details of reportable segment
Number of reportable segments	2
Operating revenues	342,931,000	336,725,000	327,416,000
Operating income (loss)	86,605,000	83,678,000	63,801,000
Utility Plant	913,137,000	891,945,000
Depreciation and amortization expense	40,197,000	37,461,000	36,600,000
Income tax expense/(benefit)	26,500,000	25,971,000	19,083,000
GSWC | Water
Details of reportable segment
Operating revenues	305,898,000	300,450,000	291,617,000
Operating income (loss)	78,104,000	77,017,000	58,121,000
Interest expense, net	19,783,000	20,990,000	17,803,000
Utility Plant	871,756,000	852,264,000	813,942,000
Depreciation and amortization expense	37,905,000	35,450,000	34,360,000
Income tax expense/(benefit)	24,231,000	24,151,000	17,042,000
Capital additions	62,500,000	73,991,000	74,264,000
GSWC | Electric
Details of reportable segment
Operating revenues	37,033,000	36,275,000	35,799,000
Operating income (loss)	8,501,000	6,661,000	5,680,000
Interest expense, net	1,533,000	1,501,000	1,498,000
Utility Plant	41,381,000	39,681,000	37,425,000
Depreciation and amortization expense	2,292,000	2,011,000	2,240,000
Income tax expense/(benefit)	2,269,000	1,820,000	2,041,000
Capital additions	4,331,000	4,447,000	2,700,000
CCWC | Water
Details of reportable segment
Operating income (loss)		(356,000)	(1,103,000)
Income tax expense/(benefit)		(145,000)	(449,000)
Income (loss) from discontinued operations		1,612,000	2,532,000
Capital additions			688,000
ASUS | Contracts
Details of reportable segment
Operating revenues	123,977,000	83,188,000	72,360,000
Operating income (loss)	24,608,000	11,855,000	11,487,000
Interest expense, net	179,000	372,000	(224,000)
Utility Plant	4,654,000	4,555,000	3,589,000
Depreciation and amortization expense	1,188,000	888,000	805,000
Income tax expense/(benefit)	9,437,000	4,431,000	4,535,000
Capital additions	1,273,000	1,843,000	1,398,000
AWR Parent
Details of reportable segment
Number of principal business units	3
Operating income (loss)	(119,000)	(73,000)	(366,000)
Interest expense, net	(63,000)	(41,000)	153,000
Income tax expense/(benefit)	8,000	(181,000)	(134,000)
Income (loss) from discontinued operations		$ 2,237,000	$ (426,000)