SEGMENT INFORMATION (Net Premiums) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting, Revenue Reconciling Item [Line Items]
Total net premiums earned from continuing operations	$ 1,037,451	$ 997,492	$ 936,131
Continuing Operations - Property and Casualty Insurance
Segment Reporting, Revenue Reconciling Item [Line Items]
Reinsurance assumed	16,957	15,059	17,037
Other	2,938	2,988	2,835
Total net premiums earned from continuing operations	1,037,451	997,492	936,131
Continuing Operations - Property and Casualty Insurance | Other liability
Segment Reporting, Revenue Reconciling Item [Line Items]
Net premiums earned	311,931	306,480	289,982
Continuing Operations - Property and Casualty Insurance | Fire and allied lines
Segment Reporting, Revenue Reconciling Item [Line Items]
Net premiums earned	276,193	270,716	265,221
Continuing Operations - Property and Casualty Insurance | Automobile
Segment Reporting, Revenue Reconciling Item [Line Items]
Net premiums earned	313,521	277,511	239,216
Continuing Operations - Property and Casualty Insurance | Workers' compensation
Segment Reporting, Revenue Reconciling Item [Line Items]
Net premiums earned	95,203	104,166	103,605
Continuing Operations - Property and Casualty Insurance | Fidelity and surety
Segment Reporting, Revenue Reconciling Item [Line Items]
Net premiums earned	24,437	24,981	22,507
Continuing Operations - Property and Casualty Insurance | Reinsurance assumed
Segment Reporting, Revenue Reconciling Item [Line Items]
Reinsurance assumed	13,228	10,650	12,765
Discontinued Operations | Discontinued Operations - Life Insurance
Segment Reporting, Revenue Reconciling Item [Line Items]
Other	12	48	58
Total net premiums earned from continuing operations	13,003	61,368	87,270
Discontinued Operations | Discontinued Operations - Life Insurance | Ordinary life (excluding universal life)
Segment Reporting, Revenue Reconciling Item [Line Items]
Net premiums earned	7,068	35,388	63,668
Discontinued Operations | Discontinued Operations - Life Insurance | Universal life policy fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Net premiums earned	3,363	13,145	11,577
Discontinued Operations | Discontinued Operations - Life Insurance | Immediate annuities with life contingencies
Segment Reporting, Revenue Reconciling Item [Line Items]
Net premiums earned	2,515	11,691	10,533
Discontinued Operations | Discontinued Operations - Life Insurance | Accident and health
Segment Reporting, Revenue Reconciling Item [Line Items]
Net premiums earned	$ 45	$ 1,096	$ 1,434