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Available-For-Sale And Held-To-Maturity Securities (Narrative) (Details) $ in Thousands | 3 Months Ended | 6 Months Ended |
--- | --- | --- | ---
Jun. 30, 2021 USD ($) security | Jun. 30, 2020 USD ($) | Jun. 30, 2021 USD ($) security | Jun. 30, 2020 USD ($) | Dec. 31, 2020 USD ($)
Other Than Temporary Impairment Credit Losses Recognized In Earnings [Line Items] |  |  |  |  |
Accrued interest receivable | $ 22,600 |  | $ 22,600 |  | $ 20,800
Proceeds from sale of available-for-sale securities |  | $ 203,600 |  | $ 491,900 |
Net realized gains (loss) resulting from sale of available-for-sale securities | 0 | $ 200 | 0 | $ (500) |
Transfers from available for sale securities to held to maturity | 312,900 |  | 312,900 |  |
Gain On Transfer Of securities | 0 |  |  |  |
Financial instruments pledged as collateral | $ 703,400 |  | $ 703,400 |  | 368,400
Number of available for sale securities whose amortized costs exceeded their fair values | security | 34 |  | 34 |  |
Available-for-sale Securities, Continuous | $ 6,110 |  | $ 6,110 |  |
Available-for-sale Securities, Continuous Unrealized | 1,269 |  | 1,269 |  |
Available-for-sale Securities, Continuous | $ 469,838 |  | $ 469,838 |  |
Percentage of available-for-sale portfolio | 20.60% |  | 20.60% |  |
Pledged [Member] |  |  |  |  |
Other Than Temporary Impairment Credit Losses Recognized In Earnings [Line Items] |  |  |  |  |
Trading securities pledged | $ 1,200,000 |  | $ 1,200,000 |  | 1,400,000
Other Assets [Member] |  |  |  |  |
Other Than Temporary Impairment Credit Losses Recognized In Earnings [Line Items] |  |  |  |  |
Accrued interest receivable | $ 27,000 |  | $ 27,000 |  | $ 26,000

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