Derivative Instruments - Schedule of Notional Amounts (Details) MWh in Thousands, MMBTU in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2020 MWh MMBTU	Dec. 31, 2019 MWh MMBTU
Non-trading | Natural Gas | Buy
Derivatives, Fair Value [Line Items]
Net notional volume (energy measure)	4,510	6,130
Non-trading | Natural Gas Basis | Buy
Derivatives, Fair Value [Line Items]
Net notional volume (energy measure)	5	42
Non-trading | Electricity | Buy
Derivatives, Fair Value [Line Items]
Net notional volume (energy measure) | MWh	4,678	6,015
Trading | Natural Gas | Buy
Derivatives, Fair Value [Line Items]
Net notional volume (energy measure)	154	204
Trading | Natural Gas Basis | Sell
Derivatives, Fair Value [Line Items]
Net notional volume (energy measure)	0	0