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Securities (Securities Available for Sale) (Details) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Sep. 30, 2018 | Sep. 30, 2017 | Sep. 30, 2018 | Sep. 30, 2017 | Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |
Proceeds from Sale of Debt Securities, Available-for-sale | $ 0 | $ 0 | $ 32,330 | $ 0 |
Securities available-for-sale, amortized cost | 3,009,386 |  | 3,009,386 |  | $ 2,763,321
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 2,259 |  | 2,259 |  | 8,480
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | 90,531 |  | 90,531 |  | 34,050
Debt Securities, Available-for-sale | 2,921,114 |  | 2,921,114 |  | 2,737,751
U.S. Government Agency and Government-Sponsored Enterprise Mortgage-Backed Securities and Collateralized Mortgage Obligations [Member] |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |
Securities available-for-sale, amortized cost | 1,997,736 |  | 1,997,736 |  | 1,752,236
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 295 |  | 295 |  | 1,815
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | 69,199 |  | 69,199 |  | 27,326
Debt Securities, Available-for-sale | 1,928,832 |  | 1,928,832 |  | 1,726,725
State and Municipal Securities [Member] |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |
Securities available-for-sale, amortized cost | 578,132 |  | 578,132 |  | 593,940
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 1,927 |  | 1,927 |  | 6,023
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | 12,241 |  | 12,241 |  | 3,959
Debt Securities, Available-for-sale | 567,818 |  | 567,818 |  | 596,004
U.S. Government and Government-Sponsored Enterprise Securities [Member] |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |
Securities available-for-sale, amortized cost | 433,267 |  | 433,267 |  | 416,894
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 37 |  | 37 |  | 642
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | 9,087 |  | 9,087 |  | 2,762
Debt Securities, Available-for-sale | 424,217 |  | 424,217 |  | 414,774
US Government Securities [Member] |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |
Securities available-for-sale, amortized cost | 251 |  | 251 |  | 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 | 4 |  | 4 |  | 3
Debt Securities, Available-for-sale | $ 247 |  | $ 247 |  | $ 248

X
- 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=82897076&loc=d3e27161-111563 + Details
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- Definition Amount, before tax, of unrealized loss 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 (c) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563 + Details
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