Derivative Financial Instruments - Interest Rate Swaps (Additional Information) (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)	Jul. 31, 2015 agreement
Credit Derivatives [Line Items]
Gain (loss) on derivative	$ 1,500	$ (500)	$ 2,200	$ (1,600)
Interest rate swap
Credit Derivatives [Line Items]
Gain (loss) on derivative	36	48	110	143
Natural gas forward contract | Not designated as hedging instrument
Credit Derivatives [Line Items]
Gain (loss) on derivative	700	(800)		(1,500)
Gain on the settlement of contracts	1,200	$ 1,100	3,700	$ 2,700
Cash flow hedging | Interest rate swap | PPA Company V
Credit Derivatives [Line Items]
Number of swap agreements entered into | agreement						9
Derivative, notional amount	$ 182,400		182,400		$ 184,200
Gain (loss) on derivative			$ (100)
Cash flow hedging | Interest rate swap maturing In 2016 | PPA Company V
Credit Derivatives [Line Items]
Number of swap agreements entered into | agreement						3
Cash flow hedging | Interest rate swap maturing September 30, 2031 | PPA Company V
Credit Derivatives [Line Items]
Number of swap agreements entered into | agreement						3
Cash flow hedging | Interest rate swap maturing December 21, 2021 | PPA Company V
Credit Derivatives [Line Items]
Number of swap agreements entered into | agreement						3