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SECURITIES AVAILABLE FOR SALE, HELD TO MATURITY, AND OTHER - Summary of Securities with Unrealized Losses (Details) - USD ($) $ in Thousands | Mar. 31, 2018 | Dec. 31, 2017
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Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Available for sale securities, less than twelve months, gross unrealized losses | $ 19,828 | $ 7,960
Available for sale securities, over twelve months, gross unrealized losses | 9,312 | 5,484
Available for sale securities, continuous unrealized loss position, accumulated loss | 29,140 | 13,444
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract] |  |
Available for sale securities, continuous unrealized loss position, less than twelve months, fair value | 966,619 | 770,082
Available for sale securities, continuous unrealized loss position, over twelve months, fair value | 198,441 | 211,750
Available for sale securities, continuous unrealized loss position, fair value | 1,165,060 | 981,832
Held-to-maturity Securities, Continuous Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Held-to-maturity securities, continuous unrealized loss position, less than twelve months, accumulated loss | 4,426 | 1,170
Held-to-maturity securities, continuous unrealized loss position, over twelve months, gross unrealized losses | 1,660 | 973
Held to maturity securities, accumulated unrecognized holding loss | 6,086 | 2,143
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value [Abstract] |  |
Held to maturity securities, accumulated unrecognized holding loss, less than twelve months, fair value | 160,409 | 17,518
Held to maturity securities, accumulated unrecognized holding loss, over twelve months, fair value | 31,585 | 32,946
Held to maturity securities, accumulated unrecognized holding loss, fair value | 191,994 | 50,464
Securities available for sale and held to maturity |  |
Held to maturity and available for sale securities continuous unrealized loss position, less than twelve months, aggregate losses | 24,254 | 9,130
Held to maturity and available for sale securities continuous unrealized loss position, less than twelve months, fair value | 1,127,028 | 787,600
Held to maturity and available for sale securities continuous unrealized loss position, over twelve months, aggregate losses | 10,972 | 6,457
Held to maturity and available for sale securities continuous unrealized loss position, over twelve months, fair value | 230,026 | 244,696
Held to maturity and available for sale securities continuous unrealized loss position, aggregate losses | 35,226 | 15,587
Held to maturity and available for sale securities continuous unrealized loss position, fair value | 1,357,054 | 1,032,296
Debt securities | Municipal bonds and obligations |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Available for sale securities, less than twelve months, gross unrealized losses | 128 | 0
Available for sale securities, over twelve months, gross unrealized losses | 593 | 206
Available for sale securities, continuous unrealized loss position, accumulated loss | 721 | 206
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract] |  |
Available for sale securities, continuous unrealized loss position, less than twelve months, fair value | 4,399 | 0
Available for sale securities, continuous unrealized loss position, over twelve months, fair value | 8,582 | 8,985
Available for sale securities, continuous unrealized loss position, fair value | 12,981 | 8,985
Held-to-maturity Securities, Continuous Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Held-to-maturity securities, continuous unrealized loss position, less than twelve months, accumulated loss | 2,779 | 35
Held-to-maturity securities, continuous unrealized loss position, over twelve months, gross unrealized losses | 201 | 55
Held to maturity securities, accumulated unrecognized holding loss | 2,980 | 90
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value [Abstract] |  |
Held to maturity securities, accumulated unrecognized holding loss, less than twelve months, fair value | 112,585 | 10,213
Held to maturity securities, accumulated unrecognized holding loss, over twelve months, fair value | 1,915 | 2,059
Held to maturity securities, accumulated unrecognized holding loss, fair value | 114,500 | 12,272
Debt securities | Agency collateralized mortgage obligations |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Available for sale securities, less than twelve months, gross unrealized losses | 16,667 | 6,849
Available for sale securities, over twelve months, gross unrealized losses | 3,149 | 2,095
Available for sale securities, continuous unrealized loss position, accumulated loss | 19,816 | 8,944
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract] |  |
Available for sale securities, continuous unrealized loss position, less than twelve months, fair value | 816,169 | 655,479
Available for sale securities, continuous unrealized loss position, over twelve months, fair value | 78,858 | 80,401
Available for sale securities, continuous unrealized loss position, fair value | 895,027 | 735,880
Held-to-maturity Securities, Continuous Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Held-to-maturity securities, continuous unrealized loss position, less than twelve months, accumulated loss | 444 | 0
Held-to-maturity securities, continuous unrealized loss position, over twelve months, gross unrealized losses | 634 | 486
Held to maturity securities, accumulated unrecognized holding loss | 1,078 | 486
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value [Abstract] |  |
Held to maturity securities, accumulated unrecognized holding loss, less than twelve months, fair value | 32,112 | 0
Held to maturity securities, accumulated unrecognized holding loss, over twelve months, fair value | 12,317 | 12,946
Held to maturity securities, accumulated unrecognized holding loss, fair value | 44,429 | 12,946
Debt securities | Agency mortgage-backed securities |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Available for sale securities, less than twelve months, gross unrealized losses | 2,715 | 765
Available for sale securities, over twelve months, gross unrealized losses | 2,808 | 1,500
Available for sale securities, continuous unrealized loss position, accumulated loss | 5,523 | 2,265
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract] |  |
Available for sale securities, continuous unrealized loss position, less than twelve months, fair value | 123,776 | 95,800
Available for sale securities, continuous unrealized loss position, over twelve months, fair value | 62,093 | 65,323
Available for sale securities, continuous unrealized loss position, fair value | 185,869 | 161,123
Held-to-maturity Securities, Continuous Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Held-to-maturity securities, continuous unrealized loss position, less than twelve months, accumulated loss | 0 | 0
Held-to-maturity securities, continuous unrealized loss position, over twelve months, gross unrealized losses | 316 | 164
Held to maturity securities, accumulated unrecognized holding loss | 316 | 164
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value [Abstract] |  |
Held to maturity securities, accumulated unrecognized holding loss, less than twelve months, fair value | 0 | 0
Held to maturity securities, accumulated unrecognized holding loss, over twelve months, fair value | 7,397 | 7,728
Held to maturity securities, accumulated unrecognized holding loss, fair value | 7,397 | 7,728
Debt securities | Agency commercial mortgage-backed securities |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Available for sale securities, less than twelve months, gross unrealized losses | 268 | 334
Available for sale securities, over twelve months, gross unrealized losses | 2,735 | 1,427
Available for sale securities, continuous unrealized loss position, accumulated loss | 3,003 | 1,761
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract] |  |
Available for sale securities, continuous unrealized loss position, less than twelve months, fair value | 13,647 | 17,379
Available for sale securities, continuous unrealized loss position, over twelve months, fair value | 46,911 | 39,268
Available for sale securities, continuous unrealized loss position, fair value | 60,558 | 56,647
Held-to-maturity Securities, Continuous Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Held-to-maturity securities, continuous unrealized loss position, less than twelve months, accumulated loss | 0 | 0
Held-to-maturity securities, continuous unrealized loss position, over twelve months, gross unrealized losses | 509 | 268
Held to maturity securities, accumulated unrecognized holding loss | 509 | 268
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value [Abstract] |  |
Held to maturity securities, accumulated unrecognized holding loss, less than twelve months, fair value | 0 | 0
Held to maturity securities, accumulated unrecognized holding loss, over twelve months, fair value | 9,956 | 10,213
Held to maturity securities, accumulated unrecognized holding loss, fair value | 9,956 | 10,213
Debt securities | Corporate bonds |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Available for sale securities, less than twelve months, gross unrealized losses | 32 | 1
Available for sale securities, over twelve months, gross unrealized losses | 0 | 236
Available for sale securities, continuous unrealized loss position, accumulated loss | 32 | 237
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract] |  |
Available for sale securities, continuous unrealized loss position, less than twelve months, fair value | 7,544 | 328
Available for sale securities, continuous unrealized loss position, over twelve months, fair value | 0 | 15,769
Available for sale securities, continuous unrealized loss position, fair value | 7,544 | 16,097
Debt securities | Trust preferred securities |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Available for sale securities, less than twelve months, gross unrealized losses |  | 0
Available for sale securities, over twelve months, gross unrealized losses |  | 0
Available for sale securities, continuous unrealized loss position, accumulated loss |  | 0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract] |  |
Available for sale securities, continuous unrealized loss position, less than twelve months, fair value |  | 0
Available for sale securities, continuous unrealized loss position, over twelve months, fair value |  | 0
Available for sale securities, continuous unrealized loss position, fair value |  | 0
Debt securities | Other bonds and obligations |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Available for sale securities, less than twelve months, gross unrealized losses | 18 | 11
Available for sale securities, over twelve months, gross unrealized losses | 27 | 20
Available for sale securities, continuous unrealized loss position, accumulated loss | 45 | 31
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract] |  |
Available for sale securities, continuous unrealized loss position, less than twelve months, fair value | 1,084 | 1,096
Available for sale securities, continuous unrealized loss position, over twelve months, fair value | 1,997 | 2,004
Available for sale securities, continuous unrealized loss position, fair value | 3,081 | 3,100
Debt securities | Tax advantaged economic development bonds |  |
Held-to-maturity Securities, Continuous Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Held-to-maturity securities, continuous unrealized loss position, less than twelve months, accumulated loss | 1,203 | 1,135
Held-to-maturity securities, continuous unrealized loss position, over twelve months, gross unrealized losses | 0 | 0
Held to maturity securities, accumulated unrecognized holding loss | 1,203 | 1,135
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value [Abstract] |  |
Held to maturity securities, accumulated unrecognized holding loss, less than twelve months, fair value | 15,712 | 7,305
Held to maturity securities, accumulated unrecognized holding loss, over twelve months, fair value | 0 | 0
Held to maturity securities, accumulated unrecognized holding loss, fair value | $ 15,712 | $ 7,305

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