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