GOODWILL, CORE DEPOSIT INTANGIBLES AND OTHER INTANGIBLE ASSETS (Carrying Amount of Intangible Assets) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 120,684	$ 112,836
Accumulated Amortization	72,249	57,412
Net Carrying Amount	48,435	55,424
Core Deposit Intangibles
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	101,185	96,821
Accumulated Amortization	58,970	48,338
Net Carrying Amount	42,215	48,483
Customer Relationship Intangible
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	1,177	1,177
Accumulated Amortization	1,009	972
Net Carrying Amount	168	205
Mortgage Servicing Rights
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	11,268	7,886
Accumulated Amortization	6,079	2,265
Net Carrying Amount	5,189	5,621
Commercial Servicing Rights
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	7,054	6,952
Accumulated Amortization	6,191	5,837
Net Carrying Amount	$ 863	$ 1,115