Regulatory Matters (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2021 USD ($)	Aug. 02, 2021	May 31, 2021	Dec. 31, 2020 USD ($)
Regulatory Matters [Line Items]
Total current regulatory assets	$ 62,188			$ 45,430
Total long-term regulatory assets	372,339			392,801
Total current regulatory liabilities	12,503			30,036
Total long-term regulatory liabilities	$ 830,788			$ 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
Petersburg Unit 1 retired MW			230
Petersburg Unit 1 retirement
Regulatory Matters [Line Items]
Total long-term regulatory assets	$ 65,600
Subsequent Event [Member]
Regulatory Matters [Line Items]
AES Indiana solar MW planned to acquire		250
AES Indiana energy storage facility MWh planned to acquire		180
AES Indiana solar MW planned to acquire		250
AES Indiana energy storage facility MWh planned to acquire		180