Derivative Financial Instruments - Interest Rate Swaps (Additional Information) (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)	Jul. 31, 2015 agreement
Interest rate swap
Credit Derivatives [Line Items]
Gain (loss) on derivative	$ 48	$ (58)	$ 143	$ 220
Cash flow hedging | Interest rate swap | PPA Company IIIb
Credit Derivatives [Line Items]
Notional amount	24,100		24,100		$ 24,700
Gain (loss) on derivative	(12)	30	(35)	31
Cash flow hedging | Interest rate swap | PPA Company V
Credit Derivatives [Line Items]
Notional amount	185,000		185,000		$ 186,600
Number of swap agreements entered into | agreement						9
Gain (loss) on derivative	$ 36	$ 40	$ 48	$ 149
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