Annual report pursuant to Section 13 and 15(d)

Our Portfolio - Equity Method Investments (Details)

v3.10.0.1
Our Portfolio - Equity Method Investments (Details) - USD ($)
$ in Thousands
Dec. 31, 2018
Dec. 31, 2017
Schedule of Equity Method Investments [Line Items]    
Carrying Value $ 471,044 $ 522,615
2007 Vento I, LLC [Member]    
Schedule of Equity Method Investments [Line Items]    
Carrying Value 92,000  
Northern Frontier, LLC [Member]    
Schedule of Equity Method Investments [Line Items]    
Carrying Value 75,000  
Buckeye Wind Energy Class B Holdings, LLC [Member]    
Schedule of Equity Method Investments [Line Items]    
Carrying Value 72,000  
3D Engie, LLC [Member]    
Schedule of Equity Method Investments [Line Items]    
Carrying Value 49,000  
Invenergy Gunsight Mountain Holdings, LLC [Member]    
Schedule of Equity Method Investments [Line Items]    
Carrying Value 37,000  
Helix Fund I, LLC [Member]    
Schedule of Equity Method Investments [Line Items]    
Carrying Value 26,000  
Other Transactions [Member]    
Schedule of Equity Method Investments [Line Items]    
Carrying Value $ 120,000