Quarterly report pursuant to Section 13 or 15(d)

Nonrecourse Debt - Schedule of Outstanding Nonrecourse Asset-Backed Debt (Detail)

v3.3.0.814
Nonrecourse Debt - Schedule of Outstanding Nonrecourse Asset-Backed Debt (Detail) - USD ($)
$ in Thousands
Sep. 30, 2015
Oct. 31, 2014
Dec. 31, 2013
Dec. 31, 2014
Debt Instrument [Line Items]        
Nonrecourse Asset-Backed Debt, Original Principal $ 288,300     $ 208,246
HASI Sustainable Yield Bond 2013-1 [Member]        
Debt Instrument [Line Items]        
Nonrecourse Asset-Backed Debt, Original Principal     $ 100,000  
Nonrecourse Asset-Backed Debt, Interest Rate     2.79%  
Nonrecourse Asset-Backed Debt, Maturity Date     2019-12  
Nonrecourse Asset-Backed Debt, Anticipated Balance at Maturity     $ 57,000  
ABS Loan Agreement [Member]        
Debt Instrument [Line Items]        
Nonrecourse Asset-Backed Debt, Original Principal   $ 115,000    
Nonrecourse Asset-Backed Debt, Interest Rate   5.74%    
Nonrecourse Asset-Backed Debt, Maturity Date   2021-09    
Nonrecourse Asset-Backed Debt, Anticipated Balance at Maturity   $ 17,000    
HASI Sustainable Yield Bond 2015-1 [Member]        
Debt Instrument [Line Items]        
Nonrecourse Asset-Backed Debt, Original Principal $ 101,000      
Nonrecourse Asset-Backed Debt, Interest Rate 4.28%      
Nonrecourse Asset-Backed Debt, Maturity Date 2034-10