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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, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Customer Interest Rate Contracts Hedging | Customer Interest Rate Contracts |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Gains/(losses) related to interest rate derivatives | $ 1,779 | $ (10,703) | $ (22,969)
Customer Interest Rate Contracts Hedging | Offsetting Upstream Interest Rate Contracts |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Gains/(losses) related to interest rate derivatives | (1,779) | 10,699 | 22,969
Debt Hedging | Interest Rate Swap |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Gains/(losses) related to interest rate derivatives | (1,648) | (7,766) | (3,552)
Debt Hedging | Term Borrowings |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Gains/(Losses) related to term borrowings | $ 1,622 | $ 7,582 | $ 3,429

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