Quarterly report pursuant to Section 13 or 15(d)

Our Portfolio - Financing Receivables, Investments and Real Estate - Analysis of Portfolio by Type of Obligor and Credit Quality (Parenthetical) (Detail)

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Our Portfolio - Financing Receivables, Investments and Real Estate - Analysis of Portfolio by Type of Obligor and Credit Quality (Parenthetical) (Detail) (USD $)
9 Months Ended
Sep. 30, 2014
Transactions
Dec. 31, 2013
Financing Receivable, Recorded Investment [Line Items]    
Allowance for credit losses $ 11,000,000 $ 11,000,000
Number of transactions 66  
Financial receivable outstanding, Average Remaining Balance 11,200,000  
Total aggregate remaining balance 17,100,000  
Maximum [Member]
   
Financing Receivable, Recorded Investment [Line Items]    
Financial receivable outstanding, Average Remaining Balance 1,000,000  
Berkshire Hathaway Inc. [Member]
   
Financing Receivable, Recorded Investment [Line Items]    
Debt security, fair value 21,100,000  
Debt security, maturity 2035  
NRG Energy [Member]
   
Financing Receivable, Recorded Investment [Line Items]    
Allowance for credit losses 11,000,000  
Senior debt investment $ 14,400,000