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
3 Months Ended
Mar. 31, 2017
Dec. 31, 2016
Financing Receivable, Recorded Investment [Line Items]    
Financing receivables $ 1,013,000  
Investments 124,859 $ 58,058
Investments 124,859 58,058
Real estate 310,000  
Equity method investments 449,165 $ 363,297
Total 1,876,000  
Average Remaining Balance 11,000  
Renewable Energy Projects [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Equity method investments 428,000  
Commercial [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Financing receivables 496,000  
Investments 22,000  
Investments 22,000  
Real estate 289,000  
Total 807,000  
Average Remaining Balance 9,000  
Commercial Non-Investment Grade [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Financing receivables 21,000  
Total 21,000  
Average Remaining Balance $ 10,000  
Credit Concentration Risk [Member] | Commercial [Member] | Debt and Real Estate Portfolio [Member]    
Financing Receivable, Recorded Investment [Line Items]    
% of Debt and Real Estate Portfolio 57.00%  
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 1.00%  
Government [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Financing receivables $ 496,000  
Investments 103,000  
Investments 103,000  
Total 599,000  
Average Remaining Balance $ 12,000  
Government [Member] | Credit Concentration Risk [Member] | Debt and Real Estate Portfolio [Member]    
Financing Receivable, Recorded Investment [Line Items]    
% of Debt and Real Estate Portfolio 42.00%  
Subtotal, Debt and Real Estate [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Financing receivables $ 1,013,000  
Investments 125,000  
Investments 125,000  
Real estate 289,000  
Total 1,427,000  
Average Remaining Balance $ 10,000  
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 449,000  
Average Remaining Balance 20,000  
Equity Method Investments [Member] | Renewable Energy Projects [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Equity method investments $ 428,000