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INVESTMENT SECURITIES, Investment Securities in a Continuous Unrealized Loss Position (Details) $ in Thousands | Mar. 31, 2019 USD ($) Position | Dec. 31, 2018 USD ($) Position
--- | --- | ---
Available-for-Sale Portfolio in Unrealized Loss Positions, Number of Positions [Abstract] |  |
Less than 12 months | Position | 13 | 169
12 months or longer | Position | 289 | 384
Total | Position | 302 | 553
Available-for-Sale Securities, in Unrealized Loss Position, Fair Value [Abstract] |  |
Less than 12 months | $ 6,111 | $ 576,527
12 months or longer | 1,176,145 | 1,584,618
Total | 1,182,256 | 2,161,145
Available-for-Sale Portfolio, Debt Maturities, Gross Unrealized Losses [Abstract] |  |
Less than 12 months | 8 | 1,156
12 months or longer | 11,151 | 25,412
Total | $ 11,159 | $ 26,568
Equity and Other Securities, Continuous Unrealized Loss Position, Number of Positions [Abstract] |  |
Less than 12 months | Position | 1 | 1
12 months or longer | Position | 0 | 0
Total | Position | 1 | 1
Equity and Other Securities, Continuous Unrealized Loss Position, Fair Value [Abstract] |  |
Less than 12 months | $ 98 | $ 82
12 months or longer | 0 | 0
Total | 98 | 82
Equity and Other Securities, Continuous Unrealized Loss Position, Gross Unrealized Losses [Abstract] |  |
Less than 12 months | 2 | 19
12 months or longer | 0 | 0
Total | $ 2 | $ 19
U.S. Treasury and Agency Securities [Member] |  |
Available-for-Sale Portfolio in Unrealized Loss Positions, Number of Positions [Abstract] |  |
Less than 12 months | Position | 0 | 7
12 months or longer | Position | 48 | 64
Total | Position | 48 | 71
Available-for-Sale Securities, in Unrealized Loss Position, Fair Value [Abstract] |  |
Less than 12 months | $ 0 | $ 473,082
12 months or longer | 862,482 | 1,213,276
Total | 862,482 | 1,686,358
Available-for-Sale Portfolio, Debt Maturities, Gross Unrealized Losses [Abstract] |  |
Less than 12 months | 0 | 682
12 months or longer | 5,268 | 14,229
Total | $ 5,268 | $ 14,911
Obligations of State and Political Subdivisions [Member] |  |
Available-for-Sale Portfolio in Unrealized Loss Positions, Number of Positions [Abstract] |  |
Less than 12 months | Position | 3 | 118
12 months or longer | Position | 20 | 97
Total | Position | 23 | 215
Available-for-Sale Securities, in Unrealized Loss Position, Fair Value [Abstract] |  |
Less than 12 months | $ 869 | $ 55,671
12 months or longer | 11,854 | 51,753
Total | 12,723 | 107,424
Available-for-Sale Portfolio, Debt Maturities, Gross Unrealized Losses [Abstract] |  |
Less than 12 months | 2 | 216
12 months or longer | 74 | 833
Total | $ 76 | $ 1,049
Government Agency Mortgage-Backed Securities [Member] |  |
Available-for-Sale Portfolio in Unrealized Loss Positions, Number of Positions [Abstract] |  |
Less than 12 months | Position | 9 | 43
12 months or longer | Position | 181 | 181
Total | Position | 190 | 224
Available-for-Sale Securities, in Unrealized Loss Position, Fair Value [Abstract] |  |
Less than 12 months | $ 5,241 | $ 47,708
12 months or longer | 242,566 | 253,931
Total | 247,807 | 301,639
Available-for-Sale Portfolio, Debt Maturities, Gross Unrealized Losses [Abstract] |  |
Less than 12 months | 6 | 258
12 months or longer | 5,192 | 9,025
Total | $ 5,198 | $ 9,283
Corporate Debt Securities [Member] |  |
Available-for-Sale Portfolio in Unrealized Loss Positions, Number of Positions [Abstract] |  |
Less than 12 months | Position | 0 | 0
12 months or longer | Position | 1 | 1
Total | Position | 1 | 1
Available-for-Sale Securities, in Unrealized Loss Position, Fair Value [Abstract] |  |
Less than 12 months | $ 0 | $ 0
12 months or longer | 2,553 | 2,546
Total | 2,553 | 2,546
Available-for-Sale Portfolio, Debt Maturities, Gross Unrealized Losses [Abstract] |  |
Less than 12 months | 0 | 0
12 months or longer | 19 | 42
Total | $ 19 | $ 42
Government Agency Collateralized Mortgage Obligations [Member] |  |
Available-for-Sale Portfolio in Unrealized Loss Positions, Number of Positions [Abstract] |  |
Less than 12 months | Position | 1 | 1
12 months or longer | Position | 39 | 41
Total | Position | 40 | 42
Available-for-Sale Securities, in Unrealized Loss Position, Fair Value [Abstract] |  |
Less than 12 months | $ 1 | $ 66
12 months or longer | 56,690 | 63,112
Total | 56,691 | 63,178
Available-for-Sale Portfolio, Debt Maturities, Gross Unrealized Losses [Abstract] |  |
Less than 12 months | 0 | 0
12 months or longer | 598 | 1,283
Total | $ 598 | $ 1,283
Equity Securities, at Fair Value [Member] |  |
Equity and Other Securities, Continuous Unrealized Loss Position, Number of Positions [Abstract] |  |
Less than 12 months | Position | 1 | 1
12 months or longer | Position | 0 | 0
Total | Position | 1 | 1
Equity and Other Securities, Continuous Unrealized Loss Position, Fair Value [Abstract] |  |
Less than 12 months | $ 98 | $ 82
12 months or longer | 0 | 0
Total | 98 | 82
Equity and Other Securities, Continuous Unrealized Loss Position, Gross Unrealized Losses [Abstract] |  |
Less than 12 months | 2 | 19
12 months or longer | 0 | 0
Total | $ 2 | $ 19

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