Business Segments: (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2013		Sep. 30, 2012		Sep. 30, 2013		Sep. 30, 2012		Dec. 31, 2012
Details of reportable segment
Operating revenues	$ 130,914		$ 133,893		$ 362,161		$ 355,367
Operating income (loss)	36,164		36,480		97,421		89,972
Interest expense, net	5,667		5,599		16,886		16,679
Utility Plant	968,459		912,027		968,459		912,027		917,791
Depreciation and amortization expense	9,753	[1]	10,230	[1],[2]	29,337	[1]	31,127	[1]
Income tax expense (benefit)	9,905		12,436		30,302		29,871
Capital additions	27,870		18,722		69,059		48,169
GSWC
Details of reportable segment
Number of reportable segments					2
Operating revenues	102,781		99,525		275,214		266,069
Operating income (loss)	32,284		29,961		84,838		72,818
Utility Plant	964,425				964,425				913,137
Depreciation and amortization expense	9,474		9,941		28,480		30,283
Income tax expense (benefit)	10,251		10,030		27,557		23,352
GSWC | Water
Details of reportable segment
Operating revenues	93,932		90,976		247,234		238,334
Operating income (loss)	31,022		28,355		79,557		65,872
Interest expense, net	5,297		5,178		15,699		15,399
Utility Plant	923,521		867,310		923,521		867,310
Depreciation and amortization expense	8,900	[1]	9,405	[2]	26,739	[1]	28,527	[1]
Income tax expense (benefit)	9,812		9,795		25,574		21,358
Capital additions	27,256		17,347		67,397		44,831
GSWC | Electric
Details of reportable segment
Operating revenues	8,849		8,549		27,980		27,735
Operating income (loss)	1,262		1,606		5,281		6,946
Interest expense, net	370		397		1,124		1,186
Utility Plant	40,904		40,057		40,904		40,057
Depreciation and amortization expense	574	[1]	536	[2]	1,741	[1]	1,756	[1]
Income tax expense (benefit)	439		235		1,983		1,994
Capital additions	546		1,155		1,426		2,399
ASUS | Contracts
Details of reportable segment
Operating revenues	28,133		34,368		86,947		89,298
Operating income (loss)	3,882		6,545		12,592		17,275
Interest expense, net	71		24		224		118
Utility Plant	4,034		4,660		4,034		4,660
Depreciation and amortization expense	279	[1]	289	[2]	857	[1]	844	[1]
Income tax expense (benefit)	1,343		2,493		4,637		6,635
Capital additions	68		220		236		939
AWR Parent
Details of reportable segment
Number of reportable segments					3
Operating revenues	0		0		0		0
Operating income (loss)	(2)		(26)		(9)		(121)
Interest expense, net	(71)		0		(161)		(24)
Utility Plant	0		0		0		0
Depreciation and amortization expense	0	[1]	0	[1],[2]	0	[1]	0	[1]
Income tax expense (benefit)	(1,689)		(87)		(1,892)		(116)
Capital additions	$ 0		$ 0		$ 0		$ 0

[1] Depreciation expense computed on GSWC’s transportation equipment of $682,000 and $1,633,000 for the nine months ended September 30, 2013 and 2012, respectively, is recorded in administrative and general expenses.

[2] Depreciation expense computed on GSWC’s transportation equipment of $214,000 and $484,000 for the three months ended September 30, 2013 and 2012, respectively, is recorded in administrative and general expenses.