Annual report pursuant to Section 13 and 15(d)

Credit Facilities - Additional Information (Detail)

v3.8.0.1
Credit Facilities - Additional Information (Detail) - USD ($)
 12 Months Ended
Dec. 31, 2017
Feb. 28, 2017
Line of Credit Facility [Line Items]    
Unamortized issuance costs $ 4,000,000  
Fees for loan agreement description Fees for each loan agreement equal to 0.50%, divided by 360, multiplied by the excess of the available borrowing capacity under each component of the credit facility over the actual amount borrowed under such component.  
Default underlying financings 50.00%  
Qualifying Project Finance Loans (PF Facility) [Member]    
Line of Credit Facility [Line Items]    
London Interbank Offered Rate LIBOR plus 2.5%  
Floating interest rate 2.50%  
Applicable valuation percentages 67.00%  
London Interbank Offered Rate (LIBOR) [Member] | Qualifying Government and Institutional Loans (G&I Facility) [Member]    
Line of Credit Facility [Line Items]    
London Interbank Offered Rate ("LIBOR") plus 1.5%  
Floating interest rate 1.50%  
Fixed interest rate 1.50%  
London Interbank Offered Rate (LIBOR) [Member] | Qualifying Government and Institutional Loans (G&I Facility) [Member] | 1.5% [Member]    
Line of Credit Facility [Line Items]    
Floating interest rate 1.00%  
London Interbank Offered Rate (LIBOR) [Member] | Qualifying Project Finance Loans (PF Facility) [Member]    
Line of Credit Facility [Line Items]    
Fixed interest rate 2.50%  
London Interbank Offered Rate (LIBOR) [Member] | Qualifying Project Finance Loans (PF Facility) [Member] | 1.5% [Member]    
Line of Credit Facility [Line Items]    
Floating interest rate 1.00%  
Federal Funds Effective Swap Rate [Member] | Qualifying Government and Institutional Loans (G&I Facility) [Member] | 1.5% [Member]    
Line of Credit Facility [Line Items]    
Floating interest rate 0.50%  
Federal Funds Effective Swap Rate [Member] | Qualifying Project Finance Loans (PF Facility) [Member]    
Line of Credit Facility [Line Items]    
London Interbank Offered Rate The Federal Funds Rate plus 0.5%  
Federal Funds Effective Swap Rate [Member] | Qualifying Project Finance Loans (PF Facility) [Member] | 1.5% [Member]    
Line of Credit Facility [Line Items]    
Floating interest rate 0.50%  
Base Rate [Member] | Qualifying Project Finance Loans (PF Facility) [Member]    
Line of Credit Facility [Line Items]    
Floating interest rate 0.00%  
Credit Default Option [Member] | Qualifying Government and Institutional Loans (G&I Facility) [Member]    
Line of Credit Facility [Line Items]    
London Interbank Offered Rate LIBOR plus 2.50%  
Floating interest rate 2.50%  
Credit Default Option [Member] | Qualifying Project Finance Loans (PF Facility) [Member]    
Line of Credit Facility [Line Items]    
London Interbank Offered Rate LIBOR plus 5.00%  
Floating interest rate 5.00%  
Loans Payable [Member]    
Line of Credit Facility [Line Items]    
Short-term loans borrowed   $ 102,000,000
Senior Secured Revolving Credit Facility [Member]    
Line of Credit Facility [Line Items]    
Maximum advances on credit facilities $ 1,500,000,000  
Credit facility outstanding $ 500,000,000  
Maturity month and year 2019-07  
U.S. Federal Government [Member] | Qualifying Government and Institutional Loans (G&I Facility) [Member]    
Line of Credit Facility [Line Items]    
Applicable valuation percentages 85.00%  
Institutional [Member] | Qualifying Government and Institutional Loans (G&I Facility) [Member]    
Line of Credit Facility [Line Items]    
Applicable valuation percentages 80.00%