Fair Value Measurements - Significant Unobservable Inputs Used to Value Level 3 Instruments (Details 2) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2023 USD ($) $ / MMBTU $ / MWh	Dec. 31, 2022 USD ($) $ / MMBTU $ / MWh
Information regarding the entity's internally developed significant unobservable inputs used to value its level 3 instruments
Assets	$ 1,503,184	$ 1,552,870
Liabilities	55,744	42,446
Level 3
Information regarding the entity's internally developed significant unobservable inputs used to value its level 3 instruments
Assets	6,825	26,132
Liabilities	0	31,020
Level 3 | Forward Contracts | Commodity Contracts
Information regarding the entity's internally developed significant unobservable inputs used to value its level 3 instruments
Assets	6,825	26,132
Liabilities	$ 0	$ 31,020
Level 3 | Forward Contracts | Valuation Technique, Discounted Cash Flow | Commodity Contracts | Minimum
Information regarding the entity's internally developed significant unobservable inputs used to value its level 3 instruments
Electricity forward price (in usd per MWh) | $ / MWh	37.79	37.79
Natural gas forward price (in usd per MMBTu) | $ / MMBTU	0.10	(11.81)
Level 3 | Forward Contracts | Valuation Technique, Discounted Cash Flow | Commodity Contracts | Maximum
Information regarding the entity's internally developed significant unobservable inputs used to value its level 3 instruments
Electricity forward price (in usd per MWh) | $ / MWh	224.49	310.69
Natural gas forward price (in usd per MMBTu) | $ / MMBTU	0.13	0.00
Level 3 | Forward Contracts | Valuation Technique, Discounted Cash Flow | Commodity Contracts | Weighted-Average
Information regarding the entity's internally developed significant unobservable inputs used to value its level 3 instruments
Electricity forward price (in usd per MWh) | $ / MWh	121.24	163.92
Natural gas forward price (in usd per MMBTu) | $ / MMBTU	0.11	(5.08)
Level 3 | Forward Contracts | Valuation Technique, Discounted Cash Flow | Electricity | Commodity Contracts
Information regarding the entity's internally developed significant unobservable inputs used to value its level 3 instruments
Assets	$ 6,175	$ 26,132
Liabilities	0	1,759
Level 3 | Forward Contracts | Valuation Technique, Discounted Cash Flow | Natural Gas | Commodity Contracts
Information regarding the entity's internally developed significant unobservable inputs used to value its level 3 instruments
Assets	650	0
Liabilities	$ 0	$ 29,261