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Securities (Summary of Gross Unrealized Losses and Fair Value of the Investments with Unrealized Losses) (Details) - USD ($) $ in Thousands | Sep. 30, 2021 | Dec. 31, 2020
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Debt Securities, Available-for-sale [Line Items] |  |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months | $ 2,332,324 | $ 880,507
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | 24,252 | 6,453
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer | 229,333 | 18,597
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | 5,985 | 815
Debt Securities, Available-for-sale, Unrealized Loss Position | 2,561,657 | 899,104
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss | 30,237 | 7,268
U.S. Government Agency and Government-Sponsored Enterprise Mortgage-Backed Securities and Collateralized Mortgage Obligations [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months | 1,744,928 | 575,329
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | 15,723 | 3,728
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer | 69,031 | 18,527
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | 2,292 | 815
Debt Securities, Available-for-sale, Unrealized Loss Position | 1,813,959 | 593,856
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss | 18,015 | 4,543
Asset-backed Securities [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months | 170,492 | 143,764
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | 3,490 | 2,076
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer | 89,936 | 70
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | 2,532 | 0
Debt Securities, Available-for-sale, Unrealized Loss Position | 260,428 | 143,834
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss | 6,022 | 2,076
State and Municipal Securities [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months | 315,235 | 86,471
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | 4,406 | 592
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer | 20,961 | 0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | 566 | 0
Debt Securities, Available-for-sale, Unrealized Loss Position | 336,196 | 86,471
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss | 4,972 | 592
U.S. Government and Government-Sponsored Enterprise Securities [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months | 101,669 | 74,943
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | 633 | 57
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer | 49,405 | 0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | 595 | 0
Debt Securities, Available-for-sale, Unrealized Loss Position | 151,074 | 74,943
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss | $ 1,228 | $ 57

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