Available-for-Sale Securities Pledged as Collateral (Details) - USD ($) $ in Thousands  | 
Jun. 30, 2015  | 
Dec. 31, 2014  | 
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| Available-for-sale Securities [Abstract] | ||
| Available-for-sale Securities Pledged as Collateral | $ 12,553,084 | $ 14,159,315 | 
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- References No definition available. 
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- Definition The fair value of available-for-sale securities that serve as collateral for borrowings. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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