SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Narrative) (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2021 USD ($) item	Dec. 31, 2020 USD ($)
Accounting Policies [Line Items]
Number of bank branches | item	129
Number of ATM's | item	150
Goodwill	$ 935,560	$ 935,560
Accrued interest receivable	57,400	56,700
Available-for-sale Securities
Accounting Policies [Line Items]
Accrued interest receivable	11,700	11,900
Held-to-maturity Securities
Accounting Policies [Line Items]
Accrued interest receivable	$ 5,100	$ 6,800