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Securities (Narrative) (Details) $ in Thousands | 3 Months Ended | 9 Months Ended |  |  |
--- | --- | --- | --- | --- | ---
Sep. 30, 2021 USD ($) security shares | Jun. 30, 2020 USD ($) shares | Sep. 30, 2021 USD ($) security shares | Sep. 30, 2020 USD ($) | Jun. 30, 2021 USD ($) | Dec. 31, 2020 USD ($) | Dec. 31, 2019 USD ($)
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |  |  |
Securities transfer from AFS to HTM, fair value |  |  | $ 2,012,123 | $ 0 |  |  |
Debt Securities, Held-to-maturity, Allowance for Credit Loss | $ 0 |  | 0 |  |  | $ 0 |
Debt Securities, Available-for-sale, Allowance for Credit Loss | 0 |  | 0 |  |  |  |
Interest receivable | $ 52,886 |  | $ 52,886 |  |  | 54,831 |
Visa Class B shares, shares sold | shares |  | 17,360 |  |  |  |  |
Visa Class B shares, remaining shares | shares | 77,683 |  | 77,683 |  |  |  |
Equity Securities | $ 13,425 | $ 13,425 | $ 13,425 | $ 13,425 | $ 13,425 | 13,425 | $ 0
Available-for-sale Securities [Member] |  |  |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |  |  |
Interest receivable | 15,600 |  | 15,600 |  |  | 17,100 |
Held-to-maturity Securities |  |  |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |  |  |
Interest receivable | 4,200 |  | $ 4,200 |  |  | $ 0 |
U.S. Government Agency and Government-Sponsored Enterprise Mortgage-Backed Securities and Collateralized Mortgage Obligations [Member] |  |  |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |  |  |
Securities transfer from AFS to HTM, fair value | 2,010,000 |  |  |  |  |  |
Unrealized gain on AFS securities transferred to HTM, net of tax | $ 15,500 |  |  |  |  |  |
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions | security | 137 |  | 137 |  |  |  |
Asset-backed Securities [Member] |  |  |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |  |  |
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions | security | 21 |  | 21 |  |  |  |
State and Municipal Securities [Member] |  |  |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |  |  |
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions | security | 109 |  | 109 |  |  |  |
U.S. Government and Government-Sponsored Enterprise Securities [Member] |  |  |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |  |  |
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions | security | 11 |  | 11 |  |  |  |

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