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Investment Securities Available for Sale (Schedule of Gross Unrealized Losses on Investment Securities and Fair Value) (Details) - USD ($) $ in Thousands | Sep. 30, 2021 | Dec. 31, 2020
--- | --- | ---
Debt Securities, Available-for-sale [Line Items] |  |
Less than 12 months, fair value | $ 6,400,438 | $ 1,379,662
Less than 12 months, gross unrealized losses | (90,220) | (16,669)
12 months or longer, fair value | 736,081 | 0
12 months or longer, gross unrealized losses | (11,325) | 0
Total, fair value | 7,136,519 | 1,379,662
Total, gross unrealized losses | (101,545) | (16,669)
U.S. Treasury securities |  |
Debt Securities, Available-for-sale [Line Items] |  |
Less than 12 months, fair value | 47,398 |
Less than 12 months, gross unrealized losses | (2,435) |
12 months or longer, fair value | 0 |
12 months or longer, gross unrealized losses | 0 |
Total, fair value | 47,398 |
Total, gross unrealized losses | (2,435) |
Mortgage-backed securities issued by U.S. Government agencies |  |
Debt Securities, Available-for-sale [Line Items] |  |
Less than 12 months, fair value | 627,822 | 566,896
Less than 12 months, gross unrealized losses | (6,566) | (5,925)
12 months or longer, fair value | 162,587 | 0
12 months or longer, gross unrealized losses | (1,846) | 0
Total, fair value | 790,409 | 566,896
Total, gross unrealized losses | (8,412) | (5,925)
Mortgage-backed securities issued by U.S. Government sponsored enterprises |  |
Debt Securities, Available-for-sale [Line Items] |  |
Less than 12 months, fair value | 5,364,111 |
Less than 12 months, gross unrealized losses | (75,243) |
12 months or longer, fair value | 0 |
12 months or longer, gross unrealized losses | 0 |
Total, fair value | 5,364,111 |
Total, gross unrealized losses | (75,243) |
Collateralized mortgage obligations issued by U.S. Government agencies or sponsored enterprises |  |
Debt Securities, Available-for-sale [Line Items] |  |
Less than 12 months, fair value | 199,534 | 803,429
Less than 12 months, gross unrealized losses | (1,572) | (10,576)
12 months or longer, fair value | 573,494 | 0
12 months or longer, gross unrealized losses | (9,479) | 0
Total, fair value | 773,028 | 803,429
Total, gross unrealized losses | (11,051) | (10,576)
Commercial mortgage-backed securities issued by U.S. Government agencies or sponsored enterprises |  |
Debt Securities, Available-for-sale [Line Items] |  |
Less than 12 months, fair value | 161,573 |
Less than 12 months, gross unrealized losses | (4,404) |
12 months or longer, fair value | 0 |
12 months or longer, gross unrealized losses | 0 |
Total, fair value | 161,573 |
Total, gross unrealized losses | $ (4,404) |
Corporate debt securities and other debt securities |  |
Debt Securities, Available-for-sale [Line Items] |  |
Less than 12 months, fair value |  | 9,337
Less than 12 months, gross unrealized losses |  | (168)
12 months or longer, fair value |  | 0
12 months or longer, gross unrealized losses |  | 0
Total, fair value |  | 9,337
Total, gross unrealized losses |  | $ (168)

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