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Securities (Securities Available for Sale) (Details) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Sep. 30, 2019 | Sep. 30, 2018 | Sep. 30, 2019 | Sep. 30, 2018 | Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |  |
Proceeds from Sale of Debt Securities, Available-for-sale |  | $ 0 | $ 0 | $ 259,554 | $ 32,330 |
Debt securities available-for-sale, amortized cost |  | 3,300,143 |  | 3,300,143 |  | $ 3,210,615
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax |  | 79,026 |  | 79,026 |  | 12,799
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax |  | (11,597) |  | (11,597) |  | (55,966)
Debt securities available for sale at fair value |  | 3,367,572 |  | 3,367,572 |  | 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] |  |  |  |  |  |
Debt securities available-for-sale, amortized cost | [1] | 2,432,873 |  | 2,432,873 |  | 2,045,728
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | [1] | 61,024 |  | 61,024 |  | 8,473
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | [1] | (11,062) |  | (11,062) |  | (40,846)
Debt securities available for sale at fair value | [1] | 2,482,835 |  | 2,482,835 |  | 2,013,355
Asset-backed Securities [Member] |  |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |  |
Debt securities available-for-sale, amortized cost | [1] | 166,482 |  | 166,482 |  | 176,793
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | [1] | 5,149 |  | 5,149 |  | 763
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | [1] | (53) |  | (53) |  | (2,621)
Debt securities available for sale at fair value | [1] | 171,578 |  | 171,578 |  | 174,935
State and Municipal Securities [Member] |  |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |  |
Debt securities available-for-sale, amortized cost |  | 488,273 |  | 488,273 |  | 579,755
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax |  | 9,471 |  | 9,471 |  | 2,328
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax |  | (430) |  | (430) |  | (7,760)
Debt securities available for sale at fair value |  | 497,314 |  | 497,314 |  | 574,323
U.S. Government and Government-Sponsored Enterprise Securities [Member] |  |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |  |
Debt securities available-for-sale, amortized cost |  | 212,265 |  | 212,265 |  | 408,088
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax |  | 3,382 |  | 3,382 |  | 1,235
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax |  | (52) |  | (52) |  | (4,736)
Debt securities available for sale at fair value |  | 215,595 |  | 215,595 |  | 404,587
US Government Securities [Member] |  |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |  |
Debt securities available-for-sale, amortized cost |  | 250 |  | 250 |  | 251
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax |  | 0 |  | 0 |  | 0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax |  | 0 |  | 0 |  | (3)
Debt securities available for sale at fair value |  | $ 250 |  | $ 250 |  | $ 248
[1] | Beginning July 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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