INCOME TAXES - Components of Deferred Income Taxes (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Deferred tax assets
Allowance for credit losses	$ 59,643	$ 9,596
Deferred compensation	5,722	3,459
Deferred Tax Assets Tax Deferred Expense Deferred Loan Fees	5,224	0
Deferred gain on interest rate swap	0	39
Nonaccrual interest	0	107
Purchase accounting adjustments	17,266	21,104
Other real estate owned	2,647	4,556
Net operating loss tax carryforward	17,176	18,775
Tax credit carryforwards	931	3,701
FDIC-assisted transaction adjustments	0	2,060
Capitalized costs, accrued expenses and other	2,815	4,840
Lease liability	19,314	10,619
Deferred tax assets, net of valuation allowance, total	130,738	78,856
Deferred tax liabilities
Premises and equipment	14,337	12,211
Mortgage servicing rights	35,806	25,990
Subordinated debentures	6,169	7,226
Goodwill and intangible assets	13,165	15,756
Unrealized gain on securities available for sale	9,263	5,430
Right of use lease asset	18,684	10,063
Deferred tax liabilities	97,424	76,676
Net deferred tax asset	$ 33,314	$ 2,180