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Derivatives (Gains/(Losses) on Derivatives Associated with Interest Rate Risk Management Activities) (Details) - Hedging Instruments And Hedged Items - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Customer Interest Rate Contracts Hedging | Customer Interest Rate Contracts |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Gains/(Losses) Related to Interest Rate Derivatives | $ (10,703) | $ (22,969) | $ 604
Customer Interest Rate Contracts Hedging | Offsetting Upstream Interest Rate Contracts |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Gains/(Losses) Related to Interest Rate Derivatives | 10,699 | 22,969 | (604)
Debt Hedging | Interest Rate Swap |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Gains/(Losses) Related to Interest Rate Derivatives | (7,766) | (3,552) | (23,194)
Debt Hedging | Term Borrowings |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Gains/(Losses) related to term borrowings | $ 7,582 | $ 3,429 | $ 23,414

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