Quarterly report pursuant to Section 13 or 15(d)

Our Portfolio - Analysis of Portfolio by Type of Obligor and Credit Quality (Detail)

v3.7.0.1
Our Portfolio - Analysis of Portfolio by Type of Obligor and Credit Quality (Detail) - USD ($)
$ in Thousands
6 Months Ended
Jun. 30, 2017
Dec. 31, 2016
Financing Receivable, Recorded Investment [Line Items]    
Financing receivables $ 1,140,000  
Investments 126,329 $ 58,058
Investments 126,329 58,058
Real estate 319,000  
Equity method investments 550,986 $ 363,297
Total 2,115,000  
Average Remaining Balance 12,000  
Renewable Energy Projects [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Equity method investments 530,000  
Commercial Investment Grade [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Financing receivables 482,000  
Investments 22,000  
Investments 22,000  
Real estate 298,000  
Total 802,000  
Average Remaining Balance 9,000  
Commercial Non-Investment Grade [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Financing receivables 26,000  
Total 26,000  
Average Remaining Balance $ 9,000  
Credit Concentration Risk [Member] | Commercial Investment Grade [Member] | Debt and Real Estate Portfolio [Member]    
Financing Receivable, Recorded Investment [Line Items]    
% of Debt and Real Estate Portfolio 51.00%  
Credit Concentration Risk [Member] | Commercial Non-Investment Grade [Member] | Debt and Real Estate Portfolio [Member]    
Financing Receivable, Recorded Investment [Line Items]    
% of Debt and Real Estate Portfolio 2.00%  
Government [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Financing receivables $ 632,000  
Investments 104,000  
Investments 104,000  
Total 736,000  
Average Remaining Balance $ 13,000  
Government [Member] | Credit Concentration Risk [Member] | Debt and Real Estate Portfolio [Member]    
Financing Receivable, Recorded Investment [Line Items]    
% of Debt and Real Estate Portfolio 47.00%  
Subtotal, Debt and Real Estate [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Financing receivables $ 1,140,000  
Investments 126,000  
Investments 126,000  
Real estate 298,000  
Total 1,564,000  
Average Remaining Balance $ 11,000  
Subtotal, Debt and Real Estate [Member] | Credit Concentration Risk [Member] | Debt and Real Estate Portfolio [Member]    
Financing Receivable, Recorded Investment [Line Items]    
% of Debt and Real Estate Portfolio 100.00%  
Equity Method Investments [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Real estate $ 21,000  
Total 551,000  
Average Remaining Balance 20,000  
Equity Method Investments [Member] | Renewable Energy Projects [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Equity method investments $ 530,000