Equipment Related to Power Purchase Agreements and Fuel Delivered to Customers, net - Future minimum lease payments (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2021	Mar. 31, 2020
Lessor, Lease, Description [Line Items]
Depreciation expense	$ 1.8	$ 2.1
Minimum
Lessor, Lease, Description [Line Items]
Lease term	1 year
Maximum
Lessor, Lease, Description [Line Items]
Lease term	10 years

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

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 30
-Section 50
-Paragraph 3
-Subparagraph (a)(3)
-URI http://asc.fasb.org/extlink&oid=121576215&loc=SL77919359-209981

Name:	us-gaap_LessorOperatingLeaseTermOfContract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	instant