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Securities - Debt Securities Available-for-Sale (Details) - USD ($) $ in Thousands | Dec. 31, 2020 | Dec. 31, 2019
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Debt Securities, Available-for-sale [Line Items] |  |
Debt Securities Available-for-Sale, Amortized Cost | $ 4,997,529 | $ 3,703,096
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 219,873 | 63,486
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | (7,268) | (20,440)
Debt Securities, Available-for-sale, Allowance for Credit Loss | 0 | 0
Debt Securities, Available-for-sale | 5,210,134 | 3,746,142
U.S. Government Agency and Government-Sponsored Enterprise Mortgage-Backed Securities and Collateralized Mortgage Obligations |  |
Debt Securities, Available-for-sale [Line Items] |  |
Debt Securities Available-for-Sale, Amortized Cost | 3,640,351 | 2,864,949
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 178,579 | 47,223
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | (4,543) | (19,222)
Debt Securities, Available-for-sale, Allowance for Credit Loss | 0 | 0
Debt Securities, Available-for-sale | 3,814,387 | 2,892,950
Asset-backed Securities |  |
Debt Securities, Available-for-sale [Line Items] |  |
Debt Securities Available-for-Sale, Amortized Cost | 349,904 | 194,563
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 9,651 | 2,476
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | (2,076) | (989)
Debt Securities, Available-for-sale, Allowance for Credit Loss | 0 | 0
Debt Securities, Available-for-sale | 357,479 | 196,050
State and Municipal Securities |  |
Debt Securities, Available-for-sale [Line Items] |  |
Debt Securities Available-for-Sale, Amortized Cost | 729,066 | 478,366
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 25,098 | 10,660
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | (592) | (224)
Debt Securities, Available-for-sale, Allowance for Credit Loss | 0 | 0
Debt Securities, Available-for-sale | 753,572 | 488,802
U.S. Government Agency and Government-Sponsored Enterprise Securities [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Debt Securities Available-for-Sale, Amortized Cost | 278,208 | 165,218
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 6,545 | 3,127
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | (57) | (5)
Debt Securities, Available-for-sale, Allowance for Credit Loss | 0 | 0
Debt Securities, Available-for-sale | $ 284,696 | $ 168,340

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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=121645371&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=121645371&loc=d3e27161-111563 + Details
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