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Securities (Summary of Gross Unrealized Losses and Fair Value of the Investments with Unrealized Losses) (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Debt Securities, Available-for-sale [Line Items] |  |  |
Equity Securities, FV-NI, Gain (Loss) | $ 195 | $ 0 | $ 0
Equity Securities, FV-NI, Realized Gain (Loss) | (195) |  |
Less than 12 Months Fair Value | 276,306 | 1,220,992 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss, Instant | 1,598 | 9,442 |
12 Months or More Fair Value | 1,873,565 | 948,366 |
12 Months or More Unrealized Losses | (54,368) | (24,608) |
Total Fair Value | 2,149,871 | 2,169,358 |
Total Unrealized Losses | (55,966) | (34,050) |
Equity Securities, FV-NI, Unrealized Gain (Loss) | 0 |  |
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 | 154,622 | 816,678 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss, Instant | 972 | 6,710 |
12 Months or More Fair Value | 1,301,387 | 717,211 |
12 Months or More Unrealized Losses | (42,495) | (20,616) |
Total Fair Value | 1,456,009 | 1,533,889 |
Total Unrealized Losses | (43,467) | (27,326) |
State and Municipal Securities [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Less than 12 Months Fair Value | 106,292 | 220,019 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss, Instant | 581 | 1,723 |
12 Months or More Fair Value | 280,496 | 75,172 |
12 Months or More Unrealized Losses | (7,179) | (2,236) |
Total Fair Value | 386,788 | 295,191 |
Total Unrealized Losses | (7,760) | (3,959) |
U.S. Government Agency and Government-Sponsored Enterprise Securities [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Less than 12 Months Fair Value | 15,392 | 184,046 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss, Instant | 45 | 1,006 |
12 Months or More Fair Value | 291,435 | 155,983 |
12 Months or More Unrealized Losses | (4,691) | (1,756) |
Total Fair Value | 306,827 | 340,029 |
Total Unrealized Losses | (4,736) | (2,762) |
US Government Securities [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Less than 12 Months Fair Value | 0 | 249 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss, Instant | 0 | 3 |
12 Months or More Fair Value | 247 | 0 |
12 Months or More Unrealized Losses | (3) | 0 |
Total Fair Value | 247 | 249 |
Total Unrealized Losses | $ (3) | $ (3) |

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