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Securities (Summary of Gross Unrealized Losses and Fair Value of the Investments with Unrealized Losses) (Details) - USD ($) $ in Thousands | Mar. 31, 2019 | Dec. 31, 2018
--- | --- | ---
Debt Securities, Available-for-sale [Line Items] |  |
Less than 12 Months Fair Value | $ 5,191 | $ 276,306
Less than 12 Months Unrealized Losses | (8) | (1,598)
12 Months or More Fair Value | 1,713,893 | 1,873,565
12 Months or More Unrealized Losses | (30,595) | (54,368)
Total Fair Value | 1,719,084 | 2,149,871
Total Unrealized Losses | (30,603) | (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 | 1,879 | 154,622
Less than 12 Months Unrealized Losses | (7) | (972)
12 Months or More Fair Value | 1,250,289 | 1,301,387
12 Months or More Unrealized Losses | (26,093) | (42,495)
Total Fair Value | 1,252,168 | 1,456,009
Total Unrealized Losses | (26,100) | (43,467)
State and Municipal Securities [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Less than 12 Months Fair Value | 3,312 | 106,292
Less than 12 Months Unrealized Losses | (1) | (581)
12 Months or More Fair Value | 209,604 | 280,496
12 Months or More Unrealized Losses | (2,560) | (7,179)
Total Fair Value | 212,916 | 386,788
Total Unrealized Losses | (2,561) | (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 | 253,752 | 291,435
12 Months or More Unrealized Losses | (1,940) | (4,691)
Total Fair Value | 253,752 | 306,827
Total Unrealized Losses | (1,940) | (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 | 248 | 247
12 Months or More Unrealized Losses | (2) | (3)
Total Fair Value | 248 | 247
Total Unrealized Losses | $ (2) | $ (3)

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