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GOODWILL AND IDENTIFIABLE INTANGIBLE ASSETS (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Components of goodwill [Abstract] |  |  |
Goodwill, net, beginning of period | $ 773,810 | $ 733,503 |
Goodwill, net, activity |  | 19,898 | $ 40,307
Goodwill, net, end of period | 793,708 | 773,810 | 733,503
Identifiable Intangible Assets [Abstract] |  |  |
Gross carrying amount | 159,865 | 155,741 |
Accumulated amortization | (106,925) | (92,628) |
Net carrying amount | 52,940 | 63,113 |
Estimated aggregate amortization expense for each of five succeeding fiscal years [Abstract] |  |  |
2021 | 12,640 |  |
2022 | 10,844 |  |
2023 | 9,082 |  |
2024 | 7,551 |  |
2025 | 6,374 |  |
Thereafter | 6,449 |  |
Net carrying amount | 52,940 | 63,113 |
Servicing Asset at Fair Value, Amount [Roll Forward] |  |  |
Carrying value before valuation allowance at beginning of period | 972 | 1,137 |
Additions | 715 | 17 |
Acquisitions | 122 | 196 |
Amortization | (379) | (378) |
Carrying value before valuation allowance at end of period | 1,430 | 972 | 1,137
Valuation allowance balance at beginning of period | (298) | 0 |
Impairment charges | (150) | (326) |
Impairment recoveries | 229 | 28 |
Valuation allowance balance at end of period | (219) | (298) | $ 0
Net carrying value at end of period | 1,211 | 674 |
Fair value of MSRs at end of period | 1,384 | 1,362 |
Principal balance of loans sold during the year | 79,709 | 2,204 |
Principal balance of loans serviced for others | 351,759 | 294,093 |
Custodial escrow balances maintained in connection with loans serviced for others | $ 5,583 | $ 4,596 |
Key economic assumptions used to estimate the value of the MSRs [Abstract] |  |  |
Weighted-average contractual life | 21 years 6 months | 20 years 10 months 24 days |
Weighted-average constant prepayment rate (CPR) | 30.40% | 18.70% |
Weighted-average discount rate | 2.10% | 3.00% |
Core Deposit Intangibles [Member] |  |  |
Identifiable Intangible Assets [Abstract] |  |  |
Gross carrying amount | $ 69,403 | $ 66,475 |
Accumulated amortization | (55,572) | (50,057) |
Net carrying amount | 13,831 | 16,418 |
Estimated aggregate amortization expense for each of five succeeding fiscal years [Abstract] |  |  |
Net carrying amount | 13,831 | 16,418 |
Other Intangibles [Member] |  |  |
Identifiable Intangible Assets [Abstract] |  |  |
Gross carrying amount | 90,462 | 89,266 |
Accumulated amortization | (51,353) | (42,571) |
Net carrying amount | 39,109 | 46,695 |
Estimated aggregate amortization expense for each of five succeeding fiscal years [Abstract] |  |  |
Net carrying amount | $ 39,109 | $ 46,695 |

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