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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, 2019 | Dec. 31, 2018
--- | --- | ---
Debt Securities, Available-for-sale [Line Items] |  |  |
Less than 12 Months Fair Value |  | $ 531,453 | $ 276,306
Less than 12 Months Unrealized Losses |  | (4,272) | (1,598)
12 Months or More Fair Value |  | 616,089 | 1,873,565
12 Months or More Unrealized Losses |  | (7,325) | (54,368)
Total Fair Value |  | 1,147,542 | 2,149,871
Total Unrealized Losses |  | (11,597) | (55,966)
U.S. Government Agency and Government-Sponsored Enterprise Mortgage-Backed Securities and Collateralized Mortgage Obligations [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Less than 12 Months Fair Value | [1] | 478,690 | 114,551
Less than 12 Months Unrealized Losses | [1] | (4,017) | (750)
12 Months or More Fair Value | [1] | 528,228 | 1,207,020
12 Months or More Unrealized Losses | [1] | (7,045) | (40,096)
Total Fair Value | [1] | 1,006,918 | 1,321,571
Total Unrealized Losses | [1] | (11,062) | (40,846)
Asset-backed Securities [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Less than 12 Months Fair Value | [1] | 0 | 40,071
Less than 12 Months Unrealized Losses | [1] | 0 | (222)
12 Months or More Fair Value | [1] | 6,926 | 94,367
12 Months or More Unrealized Losses | [1] | (53) | (2,399)
Total Fair Value | [1] | 6,926 | 134,438
Total Unrealized Losses | [1] | (53) | (2,621)
State and Municipal Securities [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Less than 12 Months Fair Value |  | 52,763 | 106,292
Less than 12 Months Unrealized Losses |  | (255) | (581)
12 Months or More Fair Value |  | 23,237 | 280,496
12 Months or More Unrealized Losses |  | (175) | (7,179)
Total Fair Value |  | 76,000 | 386,788
Total Unrealized Losses |  | (430) | (7,760)
US Government Corporations and Agencies Securities [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Less than 12 Months Fair Value |  | 0 | 15,392
Less than 12 Months Unrealized Losses |  | 0 | (45)
12 Months or More Fair Value |  | 57,448 | 291,435
12 Months or More Unrealized Losses |  | (52) | (4,691)
Total Fair Value |  | 57,448 | 306,827
Total Unrealized Losses |  | (52) | (4,736)
US Government Securities [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Less than 12 Months Fair Value |  | 0 | 0
Less than 12 Months Unrealized Losses |  | 0 | 0
12 Months or More Fair Value |  | 250 | 247
12 Months or More Unrealized Losses |  | 0 | (3)
Total Fair Value |  | 250 | 247
Total Unrealized Losses |  | $ 0 | $ (3)
[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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