Derivatives and Risk Management - Schedule of Energy Commodity Derivative Volumes (Details) frequency in Thousands, MWh in Thousands, MMBTU in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2020 MWh MMBTU frequency	Dec. 31, 2019 MWh MMBTU
Purchase [Member] | Physical [Member] | Electric Derivative [Member]
Energy Commodity Derivative Volumes [Line Items]
2020	0	2
2021	0	0
2022	0	0
2023	0	0
2024	0	0
Thereafter	0	0
Purchase [Member] | Physical [Member] | Gas Derivative [Member]
Energy Commodity Derivative Volumes [Line Items]
2020 | MMBTU	8,502	9,813
2021 | MMBTU	6,380	153
2022 | MMBTU	450	225
2023 | MMBTU	0	0
2024 | MMBTU	0	0
Thereafter | MMBTU	0	0
Purchase [Member] | Financial [Member] | Electric Derivative [Member]
Energy Commodity Derivative Volumes [Line Items]
2020	262	442
2021	123	0
2022	0	0
2023	0	0
2024	0	0
Thereafter	0	0
Purchase [Member] | Financial [Member] | Gas Derivative [Member]
Energy Commodity Derivative Volumes [Line Items]
2020 | MMBTU	32,730	78,803
2021 | MMBTU	54,455	25,523
2022 | MMBTU	17,080	4,725
2023 | MMBTU	2,700	0
2024 | MMBTU	0	0
Thereafter | MMBTU	0	0
Sales [Member] | Physical [Member] | Electric Derivative [Member]
Energy Commodity Derivative Volumes [Line Items]
2020	38	133
2021	0	0
2022	0	0
2023	0	0
2024	0	0
Thereafter	0	0
Sales [Member] | Physical [Member] | Gas Derivative [Member]
Energy Commodity Derivative Volumes [Line Items]
2020 | MMBTU	2,138	2,984
2021 | MMBTU	2,840	1,040
2022 | MMBTU	0	0
2023	0	0
2024	0	0
Thereafter | MMBTU	0	0
Sales [Member] | Financial [Member] | Electric Derivative [Member]
Energy Commodity Derivative Volumes [Line Items]
2020	409	1,724
2021	307	246
2022	0	0
2023	0	0
2024	0	0
Thereafter	0	0
Sales [Member] | Financial [Member] | Gas Derivative [Member]
Energy Commodity Derivative Volumes [Line Items]
2020 | MMBTU	12,650	37,848
2021 | MMBTU	34,710	13,108
2022 | MMBTU	6,020	675
2023 | MMBTU	0	0
2024	0	0
Thereafter | MMBTU	0	0