Quarterly report pursuant to Section 13 or 15(d)

Summary of Significant Accounting Policies - Additional Information (Detail)

v3.4.0.3
Summary of Significant Accounting Policies - Additional Information (Detail)
 3 Months Ended
Mar. 31, 2016
USD ($)
Segment
Mar. 31, 2015
USD ($)
Dec. 31, 2015
USD ($)
Summary Of Significant Accounting Policies [Line Items]      
Financing receivable, past due 90 days    
Cash and cash equivalents original maturity period 3 months    
Equity method investments $ 304,180,000   $ 318,769,000
Impairment of equity method investments $ 0 $ 0  
Real estate investment description To qualify as a REIT, we must meet a number of organizational and operational requirements, including a requirement that we currently distribute at least 90% of our net taxable income, excluding capital gains, to our shareholders.    
Income tax examination, description We have no examinations in progress, none are expected at this time, and years 2012 through 2014 are open.    
Uncertain tax positions $ 0   0
Accrued interest and penalties 0   $ 0
Interest and penalties recognized during the period $ 0 $ 0  
Number of segment reported | Segment 1    
2013 Plan [Member] | Performance Based Restricted Stock Award [Member]      
Summary Of Significant Accounting Policies [Line Items]      
Stock-based award vesting minimum percentage 0.00%    
Stock-based award vesting maximum percentage 150.00%    
Stock-based award, range of vesting percentage description The award earned is generally between 0% and 150% of the initial target, depending on the extent to which the performance target are met.    
Earliest Tax Year [Member]      
Summary Of Significant Accounting Policies [Line Items]      
Open tax year 2012    
Latest Tax Year [Member]      
Summary Of Significant Accounting Policies [Line Items]      
Open tax year 2014    
Wind Projects [Member]      
Summary Of Significant Accounting Policies [Line Items]      
Equity method investments $ 0    
Minimum [Member]      
Summary Of Significant Accounting Policies [Line Items]      
Percentage of taxable income distributed to stockholders 90.00%