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Investment Securities (Fair Value and Gross Unrealized Loss) (Details) - USD ($) $ in Thousands | Dec. 31, 2015 | Dec. 31, 2014
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Available for sale: |  |
Fair value, less than 12 months | $ 1,094,992 | $ 816,979
Unrealized losses, less than 12 months | (9,387) | (5,008)
Fair value, 12 months or more | 1,460,634 | 1,872,077
Unrealized losses, 12 months or more | (37,440) | (45,973)
Fair value, total | 2,555,626 | 2,689,056
Unrealized losses, total | (46,827) | (50,981)
Residential mortgage-backed securities |  |
Available for sale: |  |
Fair value, less than 12 months | 1,083,137 | 808,072
Unrealized losses, less than 12 months | (9,333) | (4,910)
Fair value, 12 months or more | 1,454,550 | 1,836,218
Unrealized losses, 12 months or more | (37,224) | (40,268)
Fair value, total | 2,537,687 | 2,644,290
Unrealized losses, total | (46,557) | (45,178)
States and political subdivisions |  |
Available for sale: |  |
Fair value, less than 12 months | 6,814 | 8,833
Unrealized losses, less than 12 months | (19) | (97)
Fair value, 12 months or more | 544 | 27,793
Unrealized losses, 12 months or more | (6) | (5,521)
Fair value, total | 7,358 | 36,626
Unrealized losses, total | (25) | (5,618)
Other |  |
Available for sale: |  |
Fair value, less than 12 months | 5,041 | 74
Unrealized losses, less than 12 months | (35) | (1)
Fair value, 12 months or more | 5,540 | 8,066
Unrealized losses, 12 months or more | (210) | (184)
Fair value, total | 10,581 | 8,140
Unrealized losses, total | $ (245) | $ (185)

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