LOANS - Narrative (Details)	9 Months Ended		12 Months Ended
	Sep. 30, 2019 USD ($) loan	Sep. 30, 2018 USD ($)	Dec. 31, 2018 USD ($) loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Purchased loan pools	$ 229,100,000		$ 262,600,000
Purchased loan pools principal balance	228,000,000.0		260,500,000
Purchased pool loans unamortized purchase premium	1,100,000		2,100,000
Allowance for loan and lease losses, purchased loan pools	619,000		732,000
Loans modified that are not troubled debt restructurings	168,600,000	$ 64,000,000.0
Minimum | Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	100,000	100,000	100,000
Troubled debt restructuring loans	100,000	100,000	100,000
Minimum | Independent Third Party Loan Review
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount of loan relationship subject to sampling for annual review	1,000,000
Consumer Installment Home Improvement Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable, net amount	404,700,000		399,900,000
Commercial Insurance Premium Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable, net amount	648,700,000		413,500,000
Purchased Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable, net amount	5,388,336,000		2,588,832,000
Purchased loans, carrying value	5,390,000,000		2,590,000,000
Purchased pool loans, principal balance, nonaccrual status	$ 0		$ 0
Number of loans accounts as an accruing troubled debt restructuring | loan	0		0
Nonaccrual loans	$ 78,762,000		$ 24,107,000
Troubled debt restructuring	21,200,000		22,200,000
Troubled debt restructurings, previous charge-offs, excluding purchased loans	1,100,000		940,000
Troubled debt restructurings principal balances	1,700,000	1,900,000
Financing receivable, modifications, subsequent default, recorded investment	1,200,000	2,400,000
Loans Excluding Purchased Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	21,739,000		17,952,000
Troubled debt restructuring	15,100,000		11,000,000.0
Troubled debt restructurings, previous charge-offs, excluding purchased loans	883,000		890,000
Allowance for loan losses allocated to troubled debt restructuring	1,600,000		$ 820,000
Troubled debt restructurings principal balances	4,983,000	2,261,000
Financing receivable, modifications, subsequent default, recorded investment	$ 843,000	$ 1,700,000