Quarterly report pursuant to Section 13 or 15(d)

Available-for-Sale Securities, at Fair Value Schedule of Realized Gain (Loss) (Details)

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Available-for-Sale Securities, at Fair Value Schedule of Realized Gain (Loss) (Details) (USD $)
3 Months Ended 6 Months Ended
Jun. 30, 2012
Jun. 30, 2011
Jun. 30, 2012
Jun. 30, 2011
Schedule of Available-for-sale Securities [Line Items]        
Available-for-sale Securities, Gross Realized Gains (Losses), Sale Proceeds $ 27,600,000   $ 197,700,000  
Available-for-sale Securities, Gross Realized Gains (Losses), Amortized Cost Sold 28,700,000   187,700,000  
Available-for-sale Securities, Gross Realized Gains 560,000 141,000 11,663,000 1,949,000
Available-for-sale Securities, Gross Realized Losses (1,629,000) (95,000) (1,629,000) (265,000)
Available-for-sale Securities, Gross Realized Gain (Loss) $ (1,069,000) $ 46,000 $ 10,034,000 $ 1,684,000