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Securities (Securities Available for Sale) (Details) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Sep. 30, 2017 | Sep. 30, 2016 | Sep. 30, 2017 | Sep. 30, 2016 | Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |
Available-for-sale Securities, Gross Realized Gains (Losses), Sale Proceeds | $ 0 | $ 37,390 | $ 0 | $ 120,800 |
Securities available-for-sale, amortized cost | 2,215,335 |  | 2,215,335 |  | $ 2,299,037
Available-for-sale Debt Securities Gross Unrealized Gain, instant | 13,644 |  | 13,644 |  | 10,231
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax | (21,106) |  | (21,106) |  | (30,691)
Securities available for sale | 2,207,873 |  | 2,207,873 |  | 2,278,577
U.S. Government Agency and Government-Sponsored Enterprise Mortgage-Backed Securities and Collateralized Mortgage Obligations [Member] |  |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |
Securities available-for-sale, amortized cost | 1,391,636 |  | 1,391,636 |  | 1,486,690
Available-for-sale Debt Securities Gross Unrealized Gain, instant | 3,143 |  | 3,143 |  | 2,760
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax | (17,362) |  | (17,362) |  | (23,718)
Securities available for sale | 1,377,417 |  | 1,377,417 |  | 1,465,732
State and Municipal Securities [Member] |  |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |
Securities available-for-sale, amortized cost | 476,702 |  | 476,702 |  | 473,914
Available-for-sale Debt Securities Gross Unrealized Gain, instant | 9,047 |  | 9,047 |  | 6,343
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax | (2,261) |  | (2,261) |  | (5,197)
Securities available for sale | 483,488 |  | 483,488 |  | 475,060
U.S. Government and Government-Sponsored Enterprise Securities [Member] |  |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |
Securities available-for-sale, amortized cost | 341,462 |  | 341,462 |  | 332,348
Available-for-sale Debt Securities Gross Unrealized Gain, instant | 1,372 |  | 1,372 |  | 1,065
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax | (1,230) |  | (1,230) |  | (1,511)
Securities available for sale | 341,604 |  | 341,604 |  | 331,902
US Government Securities [Member] |  |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |
Securities available-for-sale, amortized cost | 251 |  | 251 |  | 801
Available-for-sale Debt Securities Gross Unrealized Gain, instant | 0 |  | 0 |  | 0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax | (1) |  | (1) |  | (1)
Securities available for sale | 250 |  | 250 |  | 800
Other Securities [Member] |  |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |
Securities available-for-sale, amortized cost | 5,284 |  | 5,284 |  | 5,284
Available-for-sale Debt Securities Gross Unrealized Gain, instant | 82 |  | 82 |  | 63
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax | (252) |  | (252) |  | (264)
Securities available for sale | $ 5,114 |  | $ 5,114 |  | $ 5,083

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