Equipment Related to Power Purchase Agreements and Fuel Delivered to Customers, net - Future minimum lease payments (Details) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2021 USD ($)	Jun. 30, 2021 USD ($)
Lessor, Lease, Description [Line Items]
Depreciation expense	$ 2.0	$ 3.8
Minimum
Lessor, Lease, Description [Line Items]
Lease term	1 year	1 year
Maximum
Lessor, Lease, Description [Line Items]
Lease term	10 years	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

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