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Investment Securities - Additional Information (Details) | 3 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Sep. 30, 2021 USD ($) security | Sep. 30, 2020 USD ($) | Sep. 30, 2021 USD ($) security | Sep. 30, 2020 USD ($) | Dec. 31, 2020 USD ($)
Summary of Investment Holdings [Line Items] |  |  |  |  |
Allowance for credit losses for available-for-sale debt securities | $ 0 |  | $ 0 |  | $ 0
Accrued interest receivable | $ 25,600,000 |  | $ 25,600,000 |  | 27,000,000
Number of securities in security portfolio | security | 1,925 |  | 1,925 |  |
Number of securities in unrealized loss position | security | 329 |  | 329 |  |
Total investment securities - available-for-sale | $ 7,027,950,000 |  | $ 7,027,950,000 |  | 5,970,115,000
Unrealized losses | 73,677,000 |  | 73,677,000 |  | 11,385,000
Equity securities, at fair value | 12,427,000 |  | 12,427,000 |  | 2,547,000
Gains on equity securities | 100,000 | $ 500,000 | 300,000 | $ 1,300,000 |
Impairments on equity securities without readily determinable fair value |  |  | 0 | 0 |
Other Assets |  |  |  |  |
Summary of Investment Holdings [Line Items] |  |  |  |  |
Equity securities without readily determinable fair value | $ 124,800,000 |  | $ 124,800,000 |  | 105,800,000
Pooled trust preferred securities |  |  |  |  |
Summary of Investment Holdings [Line Items] |  |  |  |  |
Number of pooled trust preferred securities | security | 2 |  | 2 |  |
Total investment securities - available-for-sale | $ 9,367,000 |  | $ 9,367,000 |  | 7,913,000
Unrealized losses | $ 4,384,000 |  | 4,384,000 |  | $ 5,850,000
Other-than-temporary impairment loss |  |  | $ 0 | $ 0 |

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