Military Privatization (Details) $ in Thousands	3 Months Ended								12 Months Ended
Military Privatization (Details) $ in Thousands	Dec. 31, 2020 USD ($)	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Receivables from the U.S. government:
Less: allowance for doubtful accounts	$ (5,316)				$ (916)				$ (5,316)	$ (916)	$ (951)	$ (1,041)
Pretax income
Increase in pretax operating income	$ 29,277	$ 39,807	$ 35,716	$ 25,699	$ 24,724	$ 42,724	$ 39,430	$ 20,195	$ 130,499	127,073	100,983
Contracted services:
Military Privatization
Period of fixed price contracts to maintain water systems at various military bases									50 years
Number of Operating Segments									7
American States Utility Services [Member] \| Contracted services:
Pretax income
Increase in pretax operating income									$ 22,309	$ 21,990	$ 20,414