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Securities (Debt securities) (Details) - USD ($) $ in Thousands | Sep. 30, 2021 | Dec. 31, 2020
--- | --- | ---
Debt Securities, [Line Items] |  |
Debt securities available-for-sale, amortized cost | $ 4,773,742 | $ 4,997,529
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 88,414 | 219,873
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | (30,237) | (7,268)
Debt securities available for sale at fair value | 4,831,919 | 5,210,134
Debt Securities, Held-to-Maturity, Amortized Cost | 2,075,158 | 0
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain | 2,052 |
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss | 6,159 |
Debt Securities, Held-to-maturity, Fair Value | 2,071,051 | 0
U.S. Government Agency and Government-Sponsored Enterprise Mortgage-Backed Securities and Collateralized Mortgage Obligations [Member] |  |
Debt Securities, [Line Items] |  |
Debt securities available-for-sale, amortized cost | 3,333,804 | 3,640,351
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 63,072 | 178,579
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | (18,015) | (4,543)
Debt securities available for sale at fair value | 3,378,861 | 3,814,387
Debt Securities, Held-to-Maturity, Amortized Cost | 2,075,158 |
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain | 2,052 |
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss | 6,159 |
Debt Securities, Held-to-maturity, Fair Value | 2,071,051 |
Asset-backed Securities [Member] |  |
Debt Securities, [Line Items] |  |
Debt securities available-for-sale, amortized cost | 417,128 | 349,904
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 4,803 | 9,651
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | (6,022) | (2,076)
Debt securities available for sale at fair value | 415,909 | 357,479
State and Municipal Securities [Member] |  |
Debt Securities, [Line Items] |  |
Debt securities available-for-sale, amortized cost | 769,775 | 729,066
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 16,370 | 25,098
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | (4,972) | (592)
Debt securities available for sale at fair value | 781,173 | 753,572
U.S. Government and Government-Sponsored Enterprise Securities [Member] |  |
Debt Securities, [Line Items] |  |
Debt securities available-for-sale, amortized cost | 253,035 | 278,208
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 4,169 | 6,545
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | (1,228) | (57)
Debt securities available for sale at fair value | $ 255,976 | $ 284,696

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- Definition Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=123581744&loc=d3e27161-111563 + Details
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- Definition Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=123581744&loc=d3e27161-111563 + Details
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