Derivative Financial Instruments - Interest Rate Swaps (Additional Information) (Details)	12 Months Ended
	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Jul. 31, 2015 agreement
Interest rate swap
Credit Derivatives [Line Items]
Gain (loss) on derivative	$ 225,000	$ 206,000
Cash flow hedging | Interest rate swap | PPA Company IIIb
Credit Derivatives [Line Items]
Notional amount	0	24,700,000	$ 25,600,000
Gain (loss) on derivative	(82,000)	(68,000)	(64,000)
Settlement amount	200,000
Cash flow hedging | Interest rate swap | PPA Company V
Credit Derivatives [Line Items]
Notional amount	184,200,000	186,600,000	188,500,000
Gain (loss) on derivative	$ 200,000	$ 100,000	$ 100,000
Number of swap agreements entered into | agreement				9
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