Organization - Additional Information (Details)	12 Months Ended
	Dec. 31, 2018 investment_fund
Operating Leased Assets [Line Items]
Power purchase or lease agreement term	20 years
Number of types of investment funds used by the company	3
Minimum
Operating Leased Assets [Line Items]
Power purchase or lease agreement term	20 years
Maximum
Operating Leased Assets [Line Items]
Power purchase or lease agreement term	25 years