Quarterly report pursuant to Section 13 or 15(d)

Our Portfolio - Equity Method Investments (Details)

v3.10.0.1
Our Portfolio - Equity Method Investments (Details) - USD ($)
$ in Thousands
Jun. 30, 2018
Dec. 31, 2017
Schedule of Equity Method Investments [Line Items]    
Carrying Value $ 461,159 $ 522,615
Vento I, LLC [Member]    
Schedule of Equity Method Investments [Line Items]    
Carrying Value 98,000  
Northern Frontier, LLC [Member]    
Schedule of Equity Method Investments [Line Items]    
Carrying Value 97,000  
Buckeye Wind Energy Class B Holdings, LLC [Member]    
Schedule of Equity Method Investments [Line Items]    
Carrying Value 70,000  
Invenergy Gunsight Mountain Holdings, LLC [Member]    
Schedule of Equity Method Investments [Line Items]    
Carrying Value 38,000  
MM Solar Holdings, LLC [Member]    
Schedule of Equity Method Investments [Line Items]    
Carrying Value 29,000  
Helix Fund, LLC [Member]    
Schedule of Equity Method Investments [Line Items]    
Carrying Value 24,000  
Other Transactions [Member]    
Schedule of Equity Method Investments [Line Items]    
Carrying Value $ 105,000