SCHEDULE I - CONDENSED FINANCIAL INFORMATION OF PARENT (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Condensed balance sheet
Net Income (Loss) Attributable to Parent	$ 12,868,000	$ 21,006,000	$ 22,792,000	$ 12,701,000	$ 11,212,000	$ 21,639,000	$ 16,742,000	$ 10,150,000	$ 69,367,000	$ 59,743,000	$ 60,484,000
Assets
Cash and equivalents	214,000				436,000				214,000	436,000	4,364,000
Income taxes receivable and other receivables	4,737,000				17,867,000				4,737,000	17,867,000
Total current assets	155,463,000				166,875,000				155,463,000	166,875,000
Other assets	5,667,000				5,068,000				5,667,000	5,068,000
Total Assets	1,416,734,000				1,470,493,000				1,416,734,000	1,470,493,000
Liabilities and Capitalization
Notes payable to bank	59,000,000				90,000,000				59,000,000	90,000,000
Income taxes payable	225,000				149,000				225,000	149,000
Other Liabilities, Current	15,109,000				11,297,000				15,109,000	11,297,000
Other	156,662,000				177,944,000				156,662,000	177,944,000
Deferred taxes	115,703,000				224,530,000				115,703,000	224,530,000
Other	409,088,000				477,271,000				409,088,000	477,271,000
Common shareholders' equity	529,945,000				494,297,000				529,945,000	494,297,000	465,945,000	$ 506,801,000
Total Capitalization and Liabilities	1,416,734,000				1,470,493,000				1,416,734,000	1,470,493,000
Total capitalization	850,984,000				815,278,000				850,984,000	815,278,000
AWR
Condensed balance sheet
Net Income (Loss) Attributable to Parent									69,367,000	59,743,000	60,484,000
Assets
Cash and equivalents	48,000				32,000				48,000	32,000
Inter-company loan receivables	45,955,000				76,931,000				45,955,000	76,931,000
Total current assets	46,003,000				76,963,000				46,003,000	76,963,000
Investments in subsidiaries	539,332,000				506,584,000				539,332,000	506,584,000
Other assets	8,422,000				6,964,000				8,422,000	6,964,000
Total Assets	593,757,000				590,511,000				593,757,000	590,511,000
Liabilities and Capitalization
Notes payable to bank	59,000,000				90,000,000				59,000,000	90,000,000
Income taxes payable	2,780,000				4,043,000				2,780,000	4,043,000
Inter-company payable to Parent	73,000				0				73,000	0
Other Liabilities, Current	509,000				517,000				509,000	517,000
Other	62,362,000				94,560,000				62,362,000	94,560,000
Other	1,450,000				1,654,000				1,450,000	1,654,000
Income taxes payable and other liabilities	1,450,000				1,654,000				1,450,000	1,654,000
Common shareholders' equity	529,945,000				494,297,000				529,945,000	494,297,000
Total Capitalization and Liabilities	593,757,000				590,511,000				593,757,000	590,511,000
Total capitalization	529,945,000				494,297,000				529,945,000	494,297,000
Golden State Water Company [Member]
Condensed balance sheet
Net Income (Loss) Attributable to Parent	7,309,000	$ 17,336,000	$ 18,363,000	$ 10,749,000	6,432,000	$ 17,883,000	$ 13,670,000	$ 8,984,000	53,757,000	46,969,000	47,591,000
Assets
Cash and equivalents	214,000				209,000				214,000	209,000
Income taxes receivable and other receivables	6,590,000				21,856,000				6,590,000	21,856,000
Total current assets	101,244,000				112,257,000				101,244,000	112,257,000
Other assets	5,683,000				4,906,000				5,683,000	4,906,000
Total Assets	1,326,823,000				1,384,178,000				1,326,823,000	1,384,178,000
Liabilities and Capitalization
Inter-company payable to Parent	34,836,000				61,726,000				34,836,000	61,726,000
Other Liabilities, Current	14,705,000				10,925,000				14,705,000	10,925,000
Other	117,334,000				135,971,000				117,334,000	135,971,000
Deferred taxes	120,780,000				227,798,000				120,780,000	227,798,000
Other	414,076,000				480,456,000				414,076,000	480,456,000
Common shareholders' equity	474,374,000				446,770,000				474,374,000	446,770,000	$ 423,730,000	$ 435,190,000
Total Capitalization and Liabilities	1,326,823,000				1,384,178,000				1,326,823,000	1,384,178,000
Total capitalization	795,413,000				767,751,000				795,413,000	767,751,000
Notes Payable, Other Payables [Member] | Notes Receivable | Golden State Water Company [Member]
Assets
Notes Receivable, Related Parties, Current	$ 0				$ 0				$ 0	$ 0
Syndicated Revolving Credit Facility [Member] | AWR
Condensed balance sheet
Total funded debt ratio									42.00%
Minimum [Member] | Syndicated Revolving Credit Facility [Member] | AWR
Condensed balance sheet
Total funded debt ratio									65.00%
Maximum | Syndicated Revolving Credit Facility [Member]
Condensed balance sheet
Total funded debt ratio									65.00%
Maximum | Syndicated Revolving Credit Facility [Member] | AWR
Condensed balance sheet
Total funded debt ratio									100.00%