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Derivatives (Derivatives Associated with Fixed Income Trading Activities) (Details) - USD ($) $ in Thousands | Dec. 31, 2017 | Dec. 31, 2016
--- | --- | ---
Customer Interest Rate Contracts |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |
Notional | $ 2,026,753 | $ 1,697,992
Assets | 22,097 | 39,495
Liabilities | 18,323 | 14,996
Offsetting Upstream Interest Rate Contracts |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |
Notional | 2,026,753 | 1,697,992
Assets | 17,931 | 14,996
Liabilities | 20,720 | 39,495
Option Contracts Purchased | Short |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |
Notional |  | 5,000
Assets |  | 0
Liabilities |  | 8
Option Contracts Purchased | Long |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |
Notional | 20,000 | 17,500
Assets | 15 | 63
Liabilities | 0 | 0
Forwards and Futures Purchased |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |
Notional | 6,257,140 | 2,916,750
Assets | 4,354 | 6,257
Liabilities | 5,526 | 26,659
Forwards and Futures Sold |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |
Notional | 6,292,012 | 3,085,396
Assets | 5,806 | 27,330
Liabilities | $ 4,010 | $ 6,615

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- Definition Fair value as of the balance sheet date of interest rate derivative assets, which includes all such derivative instruments in hedging and nonhedging relationships that are recognized as assets. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 10 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13433-108611 + Details
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