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STOCKHOLDERS' EQUITY (Change in Accumulated Other Comprehensive Income) (Details) - USD ($) | 3 Months Ended | 12 Months Ended
--- | --- | ---
Jun. 30, 2018 | Mar. 31, 2018 | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
AOCI Attributable to Parent, Net of Tax [Roll Forward] |  |  |  |  |
Beginning balance |  | $ 1,046,329,000 | $ 2,513,102,000 | $ 1,924,581,000 | $ 1,046,329,000
Other comprehensive income (loss) |  |  | 35,440,000 | 45,848,000 | (9,343,000)
Ending balance |  |  | 2,708,490,000 | 2,513,102,000 | 1,924,581,000
Unrealized Gains (Losses) on AFS Securities |  |  |  |  |
AOCI Attributable to Parent, Net of Tax [Roll Forward] |  |  |  |  |
Beginning balance |  | 1,874,000 | 37,877,000 | (5,949,000) | 1,874,000
Transfer of HTM securities to AFS securities |  |  |  |  | 2,785,000
Other comprehensive income (loss) before reclassification |  |  | 45,996,000 | 49,890,000 | (10,711,000)
Amounts reclassified from AOCI into earnings |  |  | (9,712,000) | (6,064,000) | (362,000)
Other comprehensive income (loss) |  |  | 36,284,000 | 43,826,000 | (11,073,000)
Ending balance |  |  | 74,161,000 | 37,877,000 | (5,949,000)
Unrealized Gains (Losses) for AFS Securities Transferred to HTM |  |  |  |  |
AOCI Attributable to Parent, Net of Tax [Roll Forward] |  |  |  |  |
Beginning balance |  | 2,705,000 | 75,000 | 95,000 | 2,705,000
Transfer of HTM securities to AFS securities |  |  |  |  | (2,785,000)
Other comprehensive income (loss) before reclassification |  |  | 0 | 0 | 0
Amounts reclassified from AOCI into earnings |  |  | (20,000) | (20,000) | (408,000)
Other comprehensive income (loss) |  |  | (20,000) | (20,000) | (408,000)
Ending balance |  |  | 55,000 | 75,000 | 95,000
Change in Fair Value of Cash Flow Hedges |  |  |  |  |
AOCI Attributable to Parent, Net of Tax [Roll Forward] |  |  |  |  |
Beginning balance |  | (4,361,000) | (782,000) | (3,393,000) | (4,361,000)
Transfer of HTM securities to AFS securities |  |  |  |  | 0
Other comprehensive income (loss) before reclassification |  |  | (699,000) | (5,103,000) | 1,087,000
Amounts reclassified from AOCI into earnings |  |  | 1,481,000 | 7,714,000 | 975,000
Other comprehensive income (loss) |  |  | 782,000 | 2,611,000 | 2,062,000
Ending balance |  |  |  | (782,000) | (3,393,000)
Unrealized Gains (Losses) on BOLI |  |  |  |  |
AOCI Attributable to Parent, Net of Tax [Roll Forward] |  |  |  |  |
Beginning balance |  | (1,102,000) | (1,595,000) | (1,026,000) | (1,102,000)
Transfer of HTM securities to AFS securities |  |  |  |  | 0
Other comprehensive income (loss) before reclassification |  |  | (2,098,000) | (646,000) | 0
Amounts reclassified from AOCI into earnings |  |  | 492,000 | 77,000 | 76,000
Other comprehensive income (loss) |  |  | (1,606,000) | (569,000) | 76,000
Ending balance |  |  | (3,201,000) | (1,595,000) | (1,026,000)
Accumulated Other Comprehensive Income (Loss) |  |  |  |  |
AOCI Attributable to Parent, Net of Tax [Roll Forward] |  |  |  |  |
Beginning balance |  | (884,000) | 35,575,000 | (10,273,000) | (884,000)
Transfer of HTM securities to AFS securities |  |  |  |  | 0
Other comprehensive income (loss) before reclassification |  |  | 43,199,000 | 44,141,000 | (9,624,000)
Amounts reclassified from AOCI into earnings |  |  | (7,759,000) | 1,707,000 | 281,000
Other comprehensive income (loss) |  |  | 35,440,000 | 45,848,000 | (9,343,000)
Ending balance |  |  | 71,015,000 | 35,575,000 | (10,273,000)
Accounting Standards Update 2018-02 |  |  |  |  |
AOCI Attributable to Parent, Net of Tax [Roll Forward] |  |  |  |  |
Amounts reclassified from AOCI into earnings | $ 107,000 |  |  |  |
Accounting Standards Update 2016-01 |  |  |  |  |
AOCI Attributable to Parent, Net of Tax [Roll Forward] |  |  |  |  |
Amounts reclassified from AOCI into earnings |  | $ 61,000 |  |  |
Cumulative Effect, Period of Adoption, Adjustment |  |  |  |  |
AOCI Attributable to Parent, Net of Tax [Roll Forward] |  |  |  |  |
Beginning balance |  |  | (1,133,000) | (416,000) |
Ending balance |  |  | $ (39,053,000) | (1,133,000) | (416,000)
Cumulative Effect, Period of Adoption, Adjustment | Unrealized Gains (Losses) on AFS Securities |  |  |  |  |
AOCI Attributable to Parent, Net of Tax [Roll Forward] |  |  |  |  |
Beginning balance |  |  |  | 465,000 |
Ending balance |  |  |  |  | 465,000
Cumulative Effect, Period of Adoption, Adjustment | Unrealized Gains (Losses) for AFS Securities Transferred to HTM |  |  |  |  |
AOCI Attributable to Parent, Net of Tax [Roll Forward] |  |  |  |  |
Beginning balance |  |  |  | 583,000 |
Ending balance |  |  |  |  | 583,000
Cumulative Effect, Period of Adoption, Adjustment | Change in Fair Value of Cash Flow Hedges |  |  |  |  |
AOCI Attributable to Parent, Net of Tax [Roll Forward] |  |  |  |  |
Beginning balance |  |  |  | (1,094,000) |
Ending balance |  |  |  |  | (1,094,000)
Cumulative Effect, Period of Adoption, Adjustment | Unrealized Gains (Losses) on BOLI |  |  |  |  |
AOCI Attributable to Parent, Net of Tax [Roll Forward] |  |  |  |  |
Beginning balance |  |  |  | 0 |
Ending balance |  |  |  |  | 0
Cumulative Effect, Period of Adoption, Adjustment | Accumulated Other Comprehensive Income (Loss) |  |  |  |  |
AOCI Attributable to Parent, Net of Tax [Roll Forward] |  |  |  |  |
Beginning balance |  |  |  | $ (46,000) |
Ending balance |  |  |  |  | $ (46,000)

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