Quarterly report pursuant to Section 13 or 15(d)

Stockholders' Equity Schedule of Accumulated Other Comprehensive Income (Loss) (Details)

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Stockholders' Equity Schedule of Accumulated Other Comprehensive Income (Loss) (Details) (USD $)
In Thousands, unless otherwise specified
Mar. 31, 2013
Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale Securities, Gross Unrealized Gains $ 889,179 $ 724,696
Available-for-sale Securities, Gross Unrealized Losses (88,469) (28,238)
Available-for-sale Securities, Gross Unrealized Gain (Loss) $ 800,710 $ 696,458