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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, 2017 | Dec. 31, 2016
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Schedule of Available-for-sale Securities [Line Items] |  |
Available-for-sale Debt Securities Gross Unrealized Gain, instant | $ 13,644 | $ 10,231
Less than 12 Months Fair Value | 788,216 | 1,461,783
Less than 12 Months Unrealized Losses | (6,167) | (25,415)
12 Months or More Fair Value | 525,915 | 165,173
12 Months or More Unrealized Losses | (14,939) | (5,276)
Total Fair Value | 1,314,131 | 1,626,956
Total Unrealized Losses | (21,106) | (30,691)
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax | 21,106 | 30,691
U.S. Government Agency and Government-Sponsored Enterprise Mortgage-Backed Securities and Collateralized Mortgage Obligations [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Available-for-sale Debt Securities Gross Unrealized Gain, instant | 3,143 | 2,760
Less than 12 Months Fair Value | 537,162 | 1,029,116
Less than 12 Months Unrealized Losses | (4,765) | (18,788)
12 Months or More Fair Value | 456,330 | 159,046
12 Months or More Unrealized Losses | (12,597) | (4,930)
Total Fair Value | 993,492 | 1,188,162
Total Unrealized Losses | (17,362) | (23,718)
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax | 17,362 | 23,718
State and Municipal Securities [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Available-for-sale Debt Securities Gross Unrealized Gain, instant | 9,047 | 6,343
Less than 12 Months Fair Value | 75,499 | 211,342
Less than 12 Months Unrealized Losses | (700) | (5,064)
12 Months or More Fair Value | 45,328 | 3,384
12 Months or More Unrealized Losses | (1,561) | (133)
Total Fair Value | 120,827 | 214,726
Total Unrealized Losses | (2,261) | (5,197)
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax | 2,261 | 5,197
US Government Corporations and Agencies Securities [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Available-for-sale Debt Securities Gross Unrealized Gain, instant | 1,372 | 1,065
Less than 12 Months Fair Value | 173,027 | 218,811
Less than 12 Months Unrealized Losses | (665) | (1,511)
12 Months or More Fair Value | 21,517 | 0
12 Months or More Unrealized Losses | (565) | 0
Total Fair Value | 194,544 | 218,811
Total Unrealized Losses | (1,230) | (1,511)
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax | 1,230 | 1,511
US Government Securities [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Available-for-sale Debt Securities Gross Unrealized Gain, instant | 0 | 0
Less than 12 Months Fair Value | 250 | 251
Less than 12 Months Unrealized Losses | (1) | (1)
12 Months or More Fair Value | 0 | 0
12 Months or More Unrealized Losses | 0 | 0
Total Fair Value | 250 | 251
Total Unrealized Losses | (1) | (1)
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax | 1 | 1
Other Securities [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Available-for-sale Debt Securities Gross Unrealized Gain, instant | 82 | 63
Less than 12 Months Fair Value | 2,278 | 2,263
Less than 12 Months Unrealized Losses | (36) | (51)
12 Months or More Fair Value | 2,740 | 2,743
12 Months or More Unrealized Losses | (216) | (213)
Total Fair Value | 5,018 | 5,006
Total Unrealized Losses | (252) | (264)
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax | $ 252 | $ 264

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