LOANS AND ALLOWANCE FOR LOAN LOSSES - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Financing Receivable, Impaired [Line Items]
Total loans acquired as overdrafts	$ 1,706,395,000	$ 1,659,535,000	$ 1,359,544,000
Loans to related parties	33,663,000	56,199,000
Unfunded commitments of related party loans	13,846,000
Interest income if accrual method	637,000	333,000
Increase in allowance for loan losses due to TDRs	0	0
Troubled debt restructuring charge-offs	$ 0	0
Westbound Bank
Financing Receivable, Impaired [Line Items]
Total loans acquired as overdrafts		$ 2,000