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SECURITIES AVAILABLE FOR SALE, HELD TO MATURITY, AND OTHER - Summary of Securities Available for Sale and Held to Maturity (Details) - USD ($) $ in Thousands | Mar. 31, 2018 | Dec. 31, 2017
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Available-for-sale Debt Securities, Amortized Cost Basis [Abstract] |  |
Available-for-sale debt securities, amortized cost basis | $ 1,426,400 | $ 1,387,250
Available-for-sale debt securities, accumulated gross unrealized gain | 4,139 | 7,108
Available-for-sale debt securities, accumulated gross unrealized loss | (29,140) | (13,444)
Available-for-sale securities, debt securities | 1,401,399 | 1,380,914
Available-for-sale Equity Securities, Amortized Cost Basis [Abstract] |  |
Available-for-sale equity securities, amortized cost basis | 59,261 | 36,483
Available-for-sale equity securities, accumulated gross unrealized gain | 0 | 9,211
Available-for-sale equity securities, accumulated gross unrealized loss | 0 | (509)
Available-for-sale securities, equity securities | 59,261 | 45,185
Available-for-sale Securities, Fair Value to Amortized Cost Basis [Abstract] |  |
Available-for-sale securities, amortized cost basis | 1,485,661 | 1,423,733
Available-for-sale securities, accumulated gross unrealized gain | 4,139 | 16,319
Available-for-sale securities, accumulated gross unrealized loss | (29,140) | (13,953)
Available for sale securities | 1,460,660 | 1,426,099
Securities held to maturity |  |
Held to maturity, amortized cost basis | 395,337 | 397,103
Held to maturity securities accumulated unrecognized holding gains | 5,045 | 10,316
Held to maturity securities, accumulated unrecognized holding loss | (6,086) | (2,143)
Securities held to maturity, fair value | 394,296 | 405,276
Available-for-sale Securities and Held-to-maturity Securities [Abstract] |  |
Held to maturity and available for sale securities, amortized cost basis | 1,880,998 | 1,820,836
Held to maturity and available for sale securities, gross unrealized gain | 9,184 | 26,635
Held to maturity and available for sale securities, gross unrealized loss | (35,226) | (16,096)
Held to maturity and available for sale securities, fair value | 1,854,956 | 1,831,375
Municipal bonds and obligations |  |
Available-for-sale Debt Securities, Amortized Cost Basis [Abstract] |  |
Available-for-sale debt securities, amortized cost basis | 112,857 | 113,427
Available-for-sale debt securities, accumulated gross unrealized gain | 2,784 | 5,012
Available-for-sale debt securities, accumulated gross unrealized loss | (721) | (206)
Available-for-sale securities, debt securities | 114,920 | 118,233
Securities held to maturity |  |
Held to maturity, amortized cost basis | 269,636 | 270,310
Held to maturity securities accumulated unrecognized holding gains | 4,251 | 8,675
Held to maturity securities, accumulated unrecognized holding loss | (2,980) | (90)
Securities held to maturity, fair value | 270,907 | 278,895
Agency collateralized mortgage obligations |  |
Available-for-sale Debt Securities, Amortized Cost Basis [Abstract] |  |
Available-for-sale debt securities, amortized cost basis | 932,723 | 859,705
Available-for-sale debt securities, accumulated gross unrealized gain | 29 | 397
Available-for-sale debt securities, accumulated gross unrealized loss | (19,816) | (8,944)
Available-for-sale securities, debt securities | 912,936 | 851,158
Securities held to maturity |  |
Held to maturity, amortized cost basis | 73,207 | 73,742
Held to maturity securities accumulated unrecognized holding gains | 433 | 1,045
Held to maturity securities, accumulated unrecognized holding loss | (1,078) | (486)
Securities held to maturity, fair value | 72,562 | 74,301
Agency mortgage-backed securities |  |
Available-for-sale Debt Securities, Amortized Cost Basis [Abstract] |  |
Available-for-sale debt securities, amortized cost basis | 195,526 | 218,926
Available-for-sale debt securities, accumulated gross unrealized gain | 95 | 279
Available-for-sale debt securities, accumulated gross unrealized loss | (5,523) | (2,265)
Available-for-sale securities, debt securities | 190,098 | 216,940
Securities held to maturity |  |
Held to maturity, amortized cost basis | 7,712 | 7,892
Held to maturity securities accumulated unrecognized holding gains | 0 | 0
Held to maturity securities, accumulated unrecognized holding loss | (316) | (164)
Securities held to maturity, fair value | 7,396 | 7,728
Agency commercial mortgage-backed securities |  |
Available-for-sale Debt Securities, Amortized Cost Basis [Abstract] |  |
Available-for-sale debt securities, amortized cost basis | 63,561 | 64,025
Available-for-sale debt securities, accumulated gross unrealized gain | 0 | 41
Available-for-sale debt securities, accumulated gross unrealized loss | (3,003) | (1,761)
Available-for-sale securities, debt securities | 60,558 | 62,305
Securities held to maturity |  |
Held to maturity, amortized cost basis | 10,465 | 10,481
Held to maturity securities accumulated unrecognized holding gains | 0 | 0
Held to maturity securities, accumulated unrecognized holding loss | (509) | (268)
Securities held to maturity, fair value | 9,956 | 10,213
Tax advantaged economic development bonds |  |
Securities held to maturity |  |
Held to maturity, amortized cost basis | 33,996 | 34,357
Held to maturity securities accumulated unrecognized holding gains | 361 | 596
Held to maturity securities, accumulated unrecognized holding loss | (1,203) | (1,135)
Securities held to maturity, fair value | 33,154 | 33,818
Corporate bonds |  |
Available-for-sale Debt Securities, Amortized Cost Basis [Abstract] |  |
Available-for-sale debt securities, amortized cost basis | 100,963 | 110,076
Available-for-sale debt securities, accumulated gross unrealized gain | 861 | 882
Available-for-sale debt securities, accumulated gross unrealized loss | (32) | (237)
Available-for-sale securities, debt securities | 101,792 | 110,721
Trust preferred securities |  |
Available-for-sale Debt Securities, Amortized Cost Basis [Abstract] |  |
Available-for-sale debt securities, amortized cost basis | 11,297 | 11,334
Available-for-sale debt securities, accumulated gross unrealized gain | 266 | 343
Available-for-sale debt securities, accumulated gross unrealized loss | 0 | 0
Available-for-sale securities, debt securities | 11,563 | 11,677
Other bonds and obligations |  |
Available-for-sale Debt Securities, Amortized Cost Basis [Abstract] |  |
Available-for-sale debt securities, amortized cost basis | 9,473 | 9,757
Available-for-sale debt securities, accumulated gross unrealized gain | 104 | 154
Available-for-sale debt securities, accumulated gross unrealized loss | (45) | (31)
Available-for-sale securities, debt securities | 9,532 | 9,880
Securities held to maturity |  |
Held to maturity, amortized cost basis | 321 | 321
Held to maturity securities accumulated unrecognized holding gains | 0 | 0
Held to maturity securities, accumulated unrecognized holding loss | 0 | 0
Securities held to maturity, fair value | $ 321 | $ 321

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