Quarterly report pursuant to Section 13 or 15(d)

Our Portfolio - Financing Receivables, Investments and Real Estate - Additional Information (Detail)

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Our Portfolio - Financing Receivables, Investments and Real Estate - Additional Information (Detail) (USD $)
3 Months Ended 6 Months Ended 6 Months Ended 3 Months Ended 6 Months Ended
Jun. 30, 2014
Investment
Jun. 30, 2013
Jun. 30, 2014
Investment
Jun. 30, 2013
Mar. 31, 2014
Dec. 31, 2013
Investment
Jun. 30, 2014
Minimum [Member]
Jun. 30, 2014
Maximum [Member]
Jun. 30, 2014
Energy Source LLC [Member]
Jun. 30, 2014
Energy Source LLC [Member]
Dec. 31, 2013
Energy Source LLC [Member]
May 31, 2013
Energy Source LLC [Member]
Financing Receivable, Recorded Investment [Line Items]                        
Financing receivables and investments $ 590,900,000   $ 590,900,000                  
Deferred funding obligations 15,400,000   15,400,000     74,700,000            
Restricted cash 9,557,000   9,557,000     49,865,000            
Available-for-sale debt securities at fair value 20,700,000   20,700,000   3,200,000              
Investments designated as held-to-maturity carrying value 14,700,000   14,700,000                  
Sale of investments designated as held-to-maturity 15,500,000                      
Realized gain on sale of investments designated as held-to-maturity 800,000                      
Available-for-sale debt securities at cost 19,600,000   19,600,000                  
Realized gain on sale of investments 1,100,000                      
Investments in unrealized loss position 0   0     0            
Intangible assets for land leases for amortize     16,900,000                  
Land recognized in acquisition 50,300,000   50,300,000                  
Lease agreement expected expirations, term             2052 2061        
Lease agreements expirations, term             2041 2043        
Financing receivable allowance                     11,000,000  
Financing receivable allowance, face amount                       24,000,000
Accrued interest income 0   0                  
Financial receivable average outstanding balance                 11,800,000 11,800,000    
Income on investment 3,093,000 1,332,000 5,475,000 1,807,000         400,000 500,000    
Maximum exposure loss for variable interest entity 800,000                      
Other financing receivables on non accrual status 0   0     0            
Provision for credit losses     $ 0 $ 0