Annual report pursuant to Section 13 and 15(d)

Our Portfolio - Equity Method Investments, Additional Information (Details)

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Our Portfolio - Equity Method Investments, Additional Information (Details) - USD ($)
3 Months Ended 12 Months Ended
Mar. 31, 2019
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Schedule of Equity Method Investments [Line Items]        
Sale of equity interest   $ 81,297,000 $ 35,849,000 $ 6,044,000
Equity method investments   498,631,000 471,044,000  
OTTI on equity method investments   0 0 $ 0
Northern Frontier Wind, LLC        
Schedule of Equity Method Investments [Line Items]        
Sale of equity interest   58,000,000    
Gain on sale of investments   28,000,000    
Investment Contracts        
Schedule of Equity Method Investments [Line Items]        
Investment in project   $ 2,000,000    
Investment Contracts | Wind Projects        
Schedule of Equity Method Investments [Line Items]        
Equity method investments     14,000,000  
U.S. Virgin Islands        
Schedule of Equity Method Investments [Line Items]        
Insurance recoveries $ 8,000,000      
Sponsor Of Wind Project        
Schedule of Equity Method Investments [Line Items]        
Impairment of ongoing project $ 8,000,000   $ 12,000,000