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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 | 3 Months Ended | 6 Months Ended
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Jun. 30, 2018 | Jun. 30, 2017 | Jun. 30, 2018 | Jun. 30, 2017
Customer Interest Rate Contracts Hedging | Customer interest rate contracts |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Gains/(Losses) related to interest rate derivatives | $ (4,459) | $ 4,099 | $ (29,183) | $ 823
Customer Interest Rate Contracts Hedging | Offsetting upstream interest rate contracts |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Gains/(Losses) related to interest rate derivatives | 4,459 | (4,099) | 29,183 | (823)
Debt Hedging | Interest rate swaps |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Gains/(Losses) related to interest rate derivatives | (1,545) | 1,808 | (8,140) | (992)
Debt Hedging | Term borrowings |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Gains/(Losses) related to term borrowings | $ 1,520 | $ (1,804) | $ 8,070 | $ 929

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