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Securities (Securities Available for Sale) (Details) - USD ($) $ in Thousands | Dec. 31, 2019 | Dec. 31, 2018
--- | --- | ---
Debt Securities, Available-for-sale [Line Items] |  |  |
Amortized Cost |  | $ 3,703,096 | $ 3,210,615
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax |  | 63,486 | 12,799
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax |  | (20,440) | (55,966)
Securities available for sale |  | 3,746,142 | 3,167,448
Debt Securities, Available-for-sale, Amortized Cost |  | 3,703,096 |
Debt Securities, Available-for-sale |  | 3,746,142 | 3,167,448
U.S. Government Agency and Government-Sponsored Enterprise Mortgage-Backed Securities and Collateralized Mortgage Obligations [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Amortized Cost | [1] | 2,864,949 | 2,045,728
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax | [1] | 47,223 | 8,473
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax | [1] | (19,222) | (40,846)
Securities available for sale | [1] | 2,892,950 | 2,013,355
Asset-backed Securities [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Debt Securities, Available-for-sale, Amortized Cost | [1] | 194,563 | 176,793
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | [1] | 2,476 | 763
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | [1] | (989) | (2,621)
Debt Securities, Available-for-sale | [1] | 196,050 | 174,935
State and Municipal Securities [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Amortized Cost |  | 478,366 | 579,755
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax |  | 10,660 | 2,328
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax |  | (224) | (7,760)
Securities available for sale |  | 488,802 | 574,323
U.S. Government Agency and Government-Sponsored Enterprise Securities [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Amortized Cost |  | 165,218 | 408,088
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax |  | 3,127 | 1,235
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax |  | (5) | (4,736)
Securities available for sale |  | $ 168,340 | 404,587
US Government Securities [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Amortized Cost |  |  | 251
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax |  |  | 0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax |  |  | (3)
Securities available for sale |  |  | $ 248
[1] | Beginning in 2019, other asset-backed securities were presented separately in this table. Prior period amounts that were previously reported in U.S. government agency and government-sponsored enterprise mortgage-backed securities and collateralized mortgage obligations have been reclassified to conform to current period presentation.

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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=118939692&loc=d3e27161-111563 + Details
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