Regulatory Matters (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Regulatory Matters [Line Items]
Total current regulatory assets	$ 47,675	$ 45,430
Total long-term regulatory assets	385,995	392,801
Total current regulatory liabilities	10,968	30,036
Total long-term regulatory liabilities	$ 835,269	$ 839,360
Preferred Resource Portfolio Coal-Fired Generation Retirement MW by 2023	630
Solar Project Acquisition MW Expected Completion in 2023	195
Estimated Projected Costs for Successful Proposed EV Portfolio Implementation	$ 5,100
Period of Time for Implementation of Services Propsed in the Electric Vehicle (EV) Portfolio	3