Business Segments (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	9 Months Ended
Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Details of reportable segment
Operating revenues	$ 133,521	$ 119,709	$ 354,480	$ 323,845
Operating income (loss)	36,480	32,420	89,972	79,554
Interest expense, net	5,599	5,992	16,679	18,307
Utility Plant	912,027	891,134	912,027	891,134	896,500
Depreciation and amortization expense	10,230	9,554	31,127	28,829
Income (loss) from discontinued operations		(18)		3,850
Capital additions	18,722	26,279	48,169	63,574
GSWC
Details of reportable segment
Number of reportable segments			2
Operating revenues	99,153	98,314	265,182	261,225
Operating income (loss)	29,961	28,400	72,818	70,149
Utility Plant	907,367		907,367		891,945
Depreciation and amortization expense	9,941	9,334	30,283	28,171
GSWC \| Water
Details of reportable segment
Operating revenues	90,604	89,570	237,447	234,047
Operating income (loss)	28,355	26,752	65,872	65,320
Interest expense, net	5,178	5,588	15,399	16,780
Utility Plant	867,310	848,647	867,310	848,647
Depreciation and amortization expense	9,405	8,832	28,527	26,662
Capital additions	17,347	24,690	44,831	59,776
GSWC \| Electric
Details of reportable segment
Operating revenues	8,549	8,744	27,735	27,178
Operating income (loss)	1,606	1,648	6,946	4,829
Interest expense, net	397	401	1,186	1,217
Utility Plant	40,057	38,063	40,057	38,063
Depreciation and amortization expense	536	502	1,756	1,509
Capital additions	1,155	684	2,399	2,313
CCWC \| Water
Details of reportable segment
Operating income (loss)				(356)
Income (loss) from discontinued operations				1,612
ASUS \| Contracts
Details of reportable segment
Operating revenues	34,368	21,395	89,298	62,620
Operating income (loss)	6,545	4,025	17,275	9,820
Interest expense, net	24	84	118	309
Utility Plant	4,660	4,424	4,660	4,424
Depreciation and amortization expense	289	220	844	658
Capital additions	220	905	939	1,485
AWR Parent
Details of reportable segment
Number of principal business units			3
Number of continuing principal business units			2
Number of contracted services			1
Operating income (loss)	(26)	(5)	(121)	(59)
Interest expense, net		(81)	(24)	1
Income (loss) from discontinued operations		$ (18)		$ 2,238

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Total expenditures for additions to long-lived assets other than financial instruments, long-term customer relationships of a financial institution, mortgage and other servicing rights, deferred policy acquisition costs, and deferred tax assets of the reportable segment; if the amount: (a) is included in the determination of segment assets reviewed by the chief operating decision maker or (b) is otherwise regularly provided to the chief operating decision maker, even if not included in the determination of segment assets.

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Amount of income (loss) from a disposal group, net of income tax before extraordinary items allocable to noncontrolling interests. Includes, net of tax, income (loss) from operations during the phase-out period, gain (loss) on disposal, provision (or any reversals of earlier provisions) for loss on disposal, and adjustments of a prior period gain (loss) on disposal.

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The net amount of nonoperating interest income (expense).

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Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues.

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Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements.

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Amount, net of accumulated depreciation, depletion and amortization, of long-lived physical assets used in the normal conduct of business and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

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Total revenue from sale of goods and services rendered during the reporting period, in the normal course of business, reduced by sales returns and allowances, and sales discounts.

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