GOODWILL AND IDENTIFIABLE INTANGIBLE ASSETS (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Identifiable Intangible Assets [Abstract]
Gross carrying amount	$ 150,518	$ 149,437
Accumulated amortization	(76,672)	(58,779)
Net carrying amount	73,846	90,658
Estimated aggregate amortization expense for each of five succeeding fiscal years [Abstract]
2019	15,296
2020	12,722
2021	10,853
2022	9,317
2023	7,814
Thereafter	17,844
Net carrying amount	73,846	90,658
Components of goodwill [Abstract]
Goodwill, beginning of period	739,254	469,966
Goodwill, activity		269,288
Goodwill, activity	(927)
Goodwill, end of period	738,327	739,254
Accumulated impairment, beginning of period	(4,824)	(4,824)
Accumulated impairment, activity	0	0
Accumulated impairment, end of period	(4,824)	(4,824)
Goodwill, net, beginning of period	734,430	465,142
Goodwill, net, activity	(927)	269,288
Goodwill, net, end of period	733,503	734,430
Servicing Asset at Fair Value, Amount [Roll Forward]
Carrying value before valuation allowance at beginning of period	1,358	1,435
Additions	228	358
Merchants acquisition	0	64
Amortization	(449)	(499)
Carrying value before valuation allowance at end of period	1,137	1,358
Valuation allowance balance at beginning of period	0	0
Impairment charges	0	0
Impairment recoveries	0	0
Valuation allowance balance at end of period	0	0
Net carrying value at end of period	1,137	1,358
Fair value of MSRs at end of period	2,397	2,473
Principal balance of loans sold during the year	18,228	32,937
Principal balance of loans serviced for others	333,862	358,518
Custodial escrow balances maintained in connection with loans serviced for others	$ 4,982	$ 5,363
Key economic assumptions used to estimate the value of the MSRs [Abstract]
Weighted-average contractual life	21 years 4 months 24 days	21 years 3 months 18 days
Weighted-average constant prepayment rate (CPR)	9.30%	11.10%
Weighted-average discount rate	3.60%	3.30%
Core Deposit Intangibles [Member]
Identifiable Intangible Assets [Abstract]
Gross carrying amount	$ 62,902	$ 62,902
Accumulated amortization	(44,306)	(37,877)
Net carrying amount	18,596	25,025
Estimated aggregate amortization expense for each of five succeeding fiscal years [Abstract]
Net carrying amount	18,596	25,025
Other Intangibles [Member]
Identifiable Intangible Assets [Abstract]
Gross carrying amount	87,616	86,535
Accumulated amortization	(32,366)	(20,902)
Net carrying amount	55,250	65,633
Estimated aggregate amortization expense for each of five succeeding fiscal years [Abstract]
Net carrying amount	$ 55,250	$ 65,633