Quarterly report pursuant to Section 13 or 15(d)

Schedule of Unrealized Loss on Investments (Details)

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Schedule of Unrealized Loss on Investments (Details) (USD $)
In Thousands, unless otherwise specified
Jun. 30, 2012
Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]    
Available-for-Sale Securities, Number of Positions 1,233 854
Assets Sold under Agreements to Repurchase, Market Value $ 11,884,236 $ 7,457,095
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value 1,257,841 1,277,120
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses (33,629) (175,348)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value 452,791 15,608
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses (56,181) (4,113)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value 1,710,632 1,292,728
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses $ (89,810) $ (179,461)
Available-for-Sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Number of Positions 194 264
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Number of Positions 95 20