LOANS - Narrative (Details)	9 Months Ended		12 Months Ended
	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($) loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Purchased loan pools	$ 274,800,000		$ 328,200,000
Purchased loan pools principal balance	272,300,000		324,400,000
Purchased pool loans unamortized purchase premium	2,500,000		3,800,000
Allowance for loan and lease losses, purchased loan pools	800,000		1,100,000
Loans modified that are not troubled debt restructurings	64,000,000	$ 36,600,000
Troubled debt restructurings excluding purchased loans	12,300,000		15,600,000
Troubled debt restructurings, previous charge-offs, excluding purchased loans	800,000		2,800,000
Allowance for loan losses allocated to troubled debt restructurings, excluding purchased loans	900,000		1,400,000
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	361,000,000		273,700,000
Commercial Insurance Premium Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable, net amount	500,400,000		482,500,000
Purchased Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable, net amount	2,711,460,000		861,595,000
Purchased loans, carrying value	2,710,000,000		861,600,000
Purchased pool loans, principal balance, nonaccrual status	4,700,000		0
Purchased loan pools, troubled debt restructuring amount	0		904,000
Nonaccrual loans	27,764,000		$ 15,428,000
Number of loans accounts as an accruing troubled debt restructuring | loan			1
Troubled debt restructurings, previous charge-offs, excluding purchased loans	1,300,000		$ 1,200,000
Troubled debt restructurings principal balances	1,900,000	1,000,000
Financing receivable, modifications, subsequent default, recorded investment	2,400,000	2,300,000
Troubled debt restructuring	23,700,000		24,900,000
Purchased Loans | 7
Accounts, Notes, Loans and Financing Receivable [Line Items]
Purchased loan pools principal balance	4,700,000		904,000
Loans Excluding Purchased Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	15,986,000		$ 14,202,000
Troubled debt restructuring loans	2,261,000	783,000
Troubled debt restructurings principal balances	2,300,000	800,000
Financing receivable, modifications, subsequent default, recorded investment	$ 1,700,000	$ 1,200,000