Quarterly report pursuant to Section 13 or 15(d)

Our Portfolio - Additional Information (Detail)

v3.7.0.1
Our Portfolio - Additional Information (Detail)
 3 Months Ended 6 Months Ended 12 Months Ended
Mar. 31, 2017
USD ($)
a
Project
Jun. 30, 2017
USD ($)
Jun. 30, 2016
USD ($)
Dec. 31, 2016
USD ($)
Financing Receivable, Recorded Investment [Line Items]        
Financing receivables, investments, real estate and equity method investments   $ 2,115,000,000    
Financing receivables on non accrual status   0   $ 0
Loan modifications that qualify as trouble debt restructurings   0   0
Provision for credit losses   0   0
Land purchased | a 4,000      
Number of solar projects | Project 20      
Portfolio cost $ 138,000,000 118,963,000 $ 7,345,000  
Amount payable upon completion of certain project related contingencies 7,000,000      
Impairment of equity method investments   0   0
Deferred funding obligations   273,447,000   170,892,000
Investment securities pledged as collateral   34,000,000   41,000,000
Financing Receivables and Investments [Member]        
Financing Receivable, Recorded Investment [Line Items]        
Deferred funding obligations   26,000,000   $ 34,000,000
American Wind Capital Company, LLC ("AWCC") [Member]        
Financing Receivable, Recorded Investment [Line Items]        
Financing receivables, carrying value that became past due   $ 10,000,000    
Real Estate Portfolio [Member]        
Financing Receivable, Recorded Investment [Line Items]        
Real estate portfolio acquired value through equity interest in joint venture $ 21,000,000      
Joint Venture [Member]        
Financing Receivable, Recorded Investment [Line Items]        
Land purchased | a 1,100      
Lease Intangibles [Member]        
Financing Receivable, Recorded Investment [Line Items]        
Portfolio cost $ 49,000,000      
Minimum [Member]        
Financing Receivable, Recorded Investment [Line Items]        
Long-term triple net leases expiration dates range   2033    
Long-term triple net leases extended expiration dates range   2047    
Maximum [Member]        
Financing Receivable, Recorded Investment [Line Items]        
Long-term triple net leases expiration dates range   2057    
Long-term triple net leases extended expiration dates range   2080