PREMISES, EQUIPMENT, AND LEASES - Components of Premises and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Subtotal	$ 126,044	$ 114,775
Less: Accumulated depreciation	81,957	70,248
Premises and equipment, net	44,087	44,527
Leasehold improvements
Property, Plant and Equipment [Line Items]
Subtotal	56,482	55,482
Furniture, fixtures, and equipment
Property, Plant and Equipment [Line Items]
Subtotal	66,403	56,134
Buildings
Property, Plant and Equipment [Line Items]
Subtotal	$ 3,159	$ 3,159