Organization - Additional Information (Details)	12 Months Ended
Dec. 31, 2017 investment_fund
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Power purchase or lease agreement term	20 years
Number of types of investment funds used by the company	3

Term of the lessor's leasing arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

No definition available.

Name:	us-gaap_LessorLeasingArrangementsOperatingLeasesTermOfContract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration