Earnings per Share/Capital Stock: (Details 2) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Capital stock
Net income	$ 26,530	$ 25,612	$ 14,072	$ 28,006	$ 26,784	$ 12,852	$ 66,214	$ 67,642
Total income available to common shareholders, basic	$ 26,439			$ 27,881			$ 65,994	$ 67,348
Additional disclosure
Options outstanding (in shares)	0			8,556			0	8,556
Anti-dilutive stock options not included in the computation of diluted EPS (in shares)							0
Common Shares issued under DRP and the 2000 and 2008 Employee Plans							42,447	81,459
Payment, Tax Withholding, Share-based Payment Arrangement							$ 1,857	$ 1,581
Weighted Average Dividends Common Stock	$ 12,356			$ 11,234			34,848	31,466
Dividends paid							$ 34,848	$ 31,466
Dividends Declared Per Common Share (in dollars per share)	$ 0.335			$ 0.305			$ 0.945	$ 0.855
Preferred Stock Dividends and Other Adjustments	$ 43			$ 50			$ 116	$ 137
Undistributed Earnings, Basic	14,131			16,722			31,250	36,039
Undistributed earnings allocated to common shareholders	14,083			16,647			31,146	35,882
Undistributed earnings allocated to participating securities	$ 48			$ 75			$ 104	$ 157
Weighted average Common Shares outstanding, basic (in shares)	36,886,000			36,835,000			36,877,000	36,804,000
Basic earnings per Common Share (in dollars per share)	$ 0.72			$ 0.76			$ 1.79	$ 1.83
Exercise of stock options and other issuances of Common Shares	$ 0		30	$ 50	291	75	$ 30	$ 416
Restricted Stock Units
Additional disclosure
Restricted stock units outstanding (in shares)	127,234			165,783			127,234	165,783
ASUS
Additional disclosure
Dividends paid	$ 12,400			$ 12,300
GOLDEN STATE WATER COMPANY
Capital stock
Net income	$ 21,143	$ 20,919	$ 11,202	$ 23,362	$ 22,298	$ 9,022	$ 53,264	$ 54,682
Additional disclosure
Payment, Tax Withholding, Share-based Payment Arrangement							1,654	1,317
Dividends paid							$ 22,500	$ 20,200