Quarterly report pursuant to Section 13 or 15(d)

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

v3.8.0.1
Our Portfolio - Equity Method Investments, Additional Information (Details) - USD ($)
3 Months Ended 12 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Dec. 31, 2017
Schedule of Equity Method Investments [Line Items]      
Equity method investments $ 490,297,000   $ 522,615,000
Loss from equity method investment 2,285,000 $ (4,171,000)  
OTTI on equity method investments 0   0
Investment Contracts [Member]      
Schedule of Equity Method Investments [Line Items]      
Investment in project 11,000,000    
Investment Contracts [Member] | Wind Projects [Member]      
Schedule of Equity Method Investments [Line Items]      
Equity method investments     $ 25,000,000
Loss from equity method investment $ 8,000,000