Equity method investments in unconsolidated affiliates - impairments (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Equity in earnings of unconsolidated affiliates
Equity Method Investments.	$ 85,000,000.0	$ 96,600,000
Chambers Cogen, LP
Equity in earnings of unconsolidated affiliates
Percentage of equity method ownership interest	40.00%
Equity Method Investments.	$ 8,000,000.0	$ 9,000,000.0
Earnings from unconsolidated affiliates
Equity in earnings of unconsolidated affiliates
Equity impairment other than temporary	$ 0
Earnings from unconsolidated affiliates | Chambers Cogen, LP
Equity in earnings of unconsolidated affiliates
Percentage of equity method ownership interest		40.00%
Equity impairment other than temporary		$ 49,200,000
Equity Method Investments.		$ 58,200,000