Annual report pursuant to Section 13 and 15(d)

The Company - Additional Information (Detail)

v3.3.1.900
The Company - Additional Information (Detail)
 1 Months Ended 12 Months Ended
Jun. 30, 2015
USD ($)
May. 31, 2014
USD ($)
Dec. 31, 2015
USD ($)
Companies
Project
Dec. 31, 2014
USD ($)
Dec. 31, 2013
USD ($)
May. 31, 2015
USD ($)
Oct. 31, 2014
USD ($)
Organization [Line Items]              
Net proceeds from offering     $ 470,000,000        
Acquisition completed date     Jan. 01, 2013        
Acquisition related costs   $ 2,500,000          
Liabilities assumed in connection with acquisitions   0          
Rental income     $ 9,107,000 $ 3,175,000      
Interest income, financing receivables     37,404,000 23,178,000 $ 15,468,000    
Follow On Public Offerings [Member]              
Organization [Line Items]              
Net proceeds from offering     $ 181,000,000        
JPMorgan [Member]              
Organization [Line Items]              
Proceeds from joint ventures $ 3,000,000            
Wind Projects [Member]              
Organization [Line Items]              
Number of limited liability companies | Companies     6        
Number of operating projects | Project     12        
Strong Upwind Holdings I, LLC [Member] | JPMorgan [Member]              
Organization [Line Items]              
Project investment amount $ 141,000,000         $ 144,000,000  
Strong Upwind Holdings I, LLC [Member] | Wind Projects [Member] | JPMorgan [Member]              
Organization [Line Items]              
Project investment amount             $ 141,000,000
American Wind Capital Company, LLC ("AWCC") [Member]              
Organization [Line Items]              
Acquisition date     May 28, 2014        
Business combination consideration paid   107,000,000          
Rental income       3,200,000      
Interest income, financing receivables       $ 1,500,000      
Series of Individually Immaterial Business Acquisitions [Member]              
Organization [Line Items]              
Business combination consideration paid   $ 19,000,000