LOANS AND LEASES, NET - Summary of Loans (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2018	Aug. 01, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	$ 3,583,297	$ 3,651,413
Net deferred loan origination fees (costs)	7,177	7,434
Total gross loans and leases	3,590,474	3,658,847
Allowance for loan and lease losses	(30,176)	(29,149)
Total loans and leases, net	3,560,298	3,629,698
Interest rate mark discounts			$ 700
National Lending | Term lending
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	695,347	641,742
National Lending | Asset based lending
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	250,633	250,465
National Lending | Factoring
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	285,776	296,507
National Lending | Lease financing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	223,715	177,915
National Lending | Insurance premium finance
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	349,299	361,105
National Lending | SBA/USDA
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	90,269	88,831
National Lending | Other commercial finance
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	99,617	99,665
National Lending | Commercial finance
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	1,994,656	1,916,230
National Lending | Consumer credit products
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	115,843	106,794
National Lending | Other consumer finance
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	154,772	161,404
National Lending | Consumer finance
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	270,615	268,198
National Lending | Tax services
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	101,739	2,240
National Lending | Warehouse finance
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	272,522	262,924
National Lending | Total National Lending
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	2,639,532	2,449,592
Community Banking
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	943,765	1,201,821
Community Banking | Commercial real estate and operating
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	682,399	883,932
Community Banking | Consumer one to four family real estate and other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	220,588	259,425
Community Banking | Agricultural real estate and operating
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	40,778	$ 58,464
Crestmark Bancorp, Inc.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Receivables acquired	276,700
Credit discounts	$ (5,000)			$ (12,300)
Interest rate mark discounts			$ (2,600)	(6,000)
Acquired loans and leases from Crestmark acquisition				$ 1,060,000