CONSOLIDATED STATEMENTS OF CHANGE IN COMMON SHAREHOLDERS' EQUITY Statement - USD ($) $ in Thousands	Total	Common Stock [Member]	Retained Earnings [Member]	GOLDEN STATE WATER COMPANY	GOLDEN STATE WATER COMPANY Common Stock [Member]	GOLDEN STATE WATER COMPANY Retained Earnings [Member]
Balance (in shares) at Dec. 31, 2018		36,758,000			165
Beginning balances at Dec. 31, 2018	$ 558,223	$ 253,689	$ 304,534	$ 503,575	$ 292,412	$ 211,163
Add:
Net income	12,852			9,022
Exercise of stock options and other issuance of Common Shares (in shares)		37,000
Exercise of stock options and other issuances of Common Shares	75	$ 75
Stock-based compensation, net of taxes paid from shares withheld from employees related to net share settlements	463	463		572	572
Dividend equivalent rights on stock-based awards not paid in cash	70	70		60	60
Deduct:
Dividends on Common Shares	10,113		10,113	10,100		10,100
Dividend equivalent rights on stock-based awards not paid in cash	70		70	60		60
Ending balances at Mar. 31, 2019	561,500	$ 254,297	307,203	503,069	$ 293,044	210,025
Balances (in shares) at Mar. 31, 2019		36,795,000			165
Balance (in shares) at Dec. 31, 2018		36,758,000			165
Beginning balances at Dec. 31, 2018	558,223	$ 253,689	304,534	503,575	$ 292,412	211,163
Add:
Net income	$ 67,642			54,682
Exercise of stock options and other issuance of Common Shares (in shares)	81,459
Exercise of stock options and other issuances of Common Shares	$ 416
Ending balances at Sep. 30, 2019	595,947	$ 255,408	340,539	539,154	$ 293,658	245,496
Balances (in shares) at Sep. 30, 2019		36,839,000			165
Balance (in shares) at Mar. 31, 2019		36,795,000			165
Beginning balances at Mar. 31, 2019	561,500	$ 254,297	307,203	503,069	$ 293,044	210,025
Add:
Net income	26,784			22,298		22,298
Exercise of stock options and other issuance of Common Shares (in shares)		37,000
Exercise of stock options and other issuances of Common Shares	291	$ 291
Stock-based compensation, net of taxes paid from shares withheld from employees related to net share settlements	331	331		257	257
Dividend equivalent rights on stock-based awards not paid in cash	50	50		44	44
Deduct:
Dividends on Common Shares	10,119		10,119	10,100		10,100
Dividend equivalent rights on stock-based awards not paid in cash	50		50	44		44
Ending balances at Jun. 30, 2019	578,787	$ 254,969	323,818	515,524	$ 293,345	222,179
Balances (in shares) at Jun. 30, 2019		36,832,000			165
Add:
Net income	28,006			23,362		23,362
Exercise of stock options and other issuance of Common Shares (in shares)		7,000
Exercise of stock options and other issuances of Common Shares	50	$ 50
Stock-based compensation, net of taxes paid from shares withheld from employees related to net share settlements	338	338		268	$ 268
Dividend equivalent rights on stock-based awards not paid in cash	51	51		45	45
Deduct:
Dividends on Common Shares	11,234		11,234
Dividend equivalent rights on stock-based awards not paid in cash	51		51	45		45
Ending balances at Sep. 30, 2019	595,947	$ 255,408	340,539	539,154	$ 293,658	245,496
Balances (in shares) at Sep. 30, 2019		36,839,000			165
Balance (in shares) at Dec. 31, 2019		36,847,000			165
Beginning balances at Dec. 31, 2019	601,530	$ 255,566	345,964	551,188	$ 293,754	257,434
Add:
Net income	14,072		14,072	11,202
Exercise of stock options and other issuance of Common Shares (in shares)		37,000
Exercise of stock options and other issuances of Common Shares	30	$ 30
Stock-based compensation, net of taxes paid from shares withheld from employees related to net share settlements	193	193		254	254
Dividend equivalent rights on stock-based awards not paid in cash	52	52		46	46
Deduct:
Dividends on Common Shares	11,242		11,242	11,250		11,250
Dividend equivalent rights on stock-based awards not paid in cash	52		52	46		46
Ending balances at Mar. 31, 2020	604,583	$ 255,841	348,742	551,394	$ 294,054	257,340
Balances (in shares) at Mar. 31, 2020					165
Balance (in shares) at Dec. 31, 2019		36,847,000			165
Beginning balances at Dec. 31, 2019	601,530	$ 255,566	345,964	551,188	$ 293,754	257,434
Add:
Net income	$ 66,214			53,264
Exercise of stock options and other issuance of Common Shares (in shares)	42,447
Exercise of stock options and other issuances of Common Shares	$ 30
Ending balances at Sep. 30, 2020	633,820	$ 256,622	377,198	511,605	$ 294,873	216,732
Balances (in shares) at Sep. 30, 2020		36,889,000			165
Balance (in shares) at Mar. 31, 2020					165
Beginning balances at Mar. 31, 2020	604,583	$ 255,841	348,742	551,394	$ 294,054	257,340
Add:
Net income	25,612		25,612	20,919
Stock-based compensation, net of taxes paid from shares withheld from employees related to net share settlements	343	343		296	296
Dividend equivalent rights on stock-based awards not paid in cash	39	39		36	36
Deduct:
Dividends on Common Shares	11,250		11,250	11,250		11,250
Dividend equivalent rights on stock-based awards not paid in cash	39		39	36		36
Ending balances at Jun. 30, 2020	619,288	$ 256,223	363,065	561,359	$ 294,386	266,973
Balances (in shares) at Jun. 30, 2020		36,884,000			165
Add:
Net income	26,530		26,530	21,143
Exercise of stock options and other issuance of Common Shares (in shares)		5,000
Exercise of stock options and other issuances of Common Shares	0	$ 0
Stock-based compensation, net of taxes paid from shares withheld from employees related to net share settlements	358	358		447	$ 447
Dividend equivalent rights on stock-based awards not paid in cash	41	41		40	40
Dividends						71,344
Deduct:
Dividends on Common Shares	12,356		12,356	71,344
Dividend equivalent rights on stock-based awards not paid in cash	41		41	40		40
Ending balances at Sep. 30, 2020	$ 633,820	$ 256,622	$ 377,198	$ 511,605	$ 294,873	$ 216,732
Balances (in shares) at Sep. 30, 2020		36,889,000			165