BASIS OF PRESENTATION (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit loss	$ 103,377	$ 66,222	$ 103,377	$ 66,222	$ 70,395	$ 119,937	$ 63,850	$ 61,963
Retained earnings	761,211		761,211		702,502
Income tax expense (benefit)	13,681	$ 7,941	27,007	$ 29,835
Off-balance, credit loss liability	14,330		14,330		248	$ 17,392
Impact of ASU 2016-13 adoption on January 1, 2020	$ 61		$ 61		$ 0
Threshold period past due, nonperforming status of loans and leases			90 days		90 days
Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit loss					$ 12,071
Retained earnings					14,900
Income tax expense (benefit)					5,000
Off-balance, credit loss liability					13,604
Impact of ASU 2016-13 adoption on January 1, 2020					158
Cumulative Effect, Period of Adoption, Adjustment | Held-to-maturity Securities
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Retained earnings					118
Income tax expense (benefit)					40
Cumulative Effect, Period of Adoption, Adjustment | Loans
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit loss					12,100
Retained earnings					4,600
Income tax expense (benefit)					1,500
Cumulative Effect, Period of Adoption, Adjustment | Loans | Financial Asset Acquired with Credit Deterioration
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit loss					6,000
Cumulative Effect, Period of Adoption, Adjustment | Unfunded Loan Commitment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Retained earnings					10,200
Income tax expense (benefit)					3,400
Off-balance, credit loss liability					$ 13,600