SEGMENT INFORMATION (Net Premiums) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting, Revenue Reconciling Item [Line Items]
Total net premiums earned from continuing operations	$ 997,492	$ 936,131	$ 851,695
Continuing Operations - Property and Casualty Insurance
Segment Reporting, Revenue Reconciling Item [Line Items]
Reinsurance assumed	15,059	17,037	18,396
Other	2,988	2,835	3,179
Total net premiums earned from continuing operations	997,492	936,131	851,695
Continuing Operations - Property and Casualty Insurance | Other liability
Segment Reporting, Revenue Reconciling Item [Line Items]
Net premiums earned	306,480	289,982	261,303
Continuing Operations - Property and Casualty Insurance | Fire and allied lines
Segment Reporting, Revenue Reconciling Item [Line Items]
Net premiums earned	270,716	265,221	246,450
Continuing Operations - Property and Casualty Insurance | Automobile
Segment Reporting, Revenue Reconciling Item [Line Items]
Net premiums earned	277,511	239,216	210,090
Continuing Operations - Property and Casualty Insurance | Workers' compensation
Segment Reporting, Revenue Reconciling Item [Line Items]
Net premiums earned	104,166	103,605	95,672
Continuing Operations - Property and Casualty Insurance | Fidelity and surety
Segment Reporting, Revenue Reconciling Item [Line Items]
Net premiums earned	24,981	22,507	21,362
Continuing Operations - Property and Casualty Insurance | Reinsurance assumed
Segment Reporting, Revenue Reconciling Item [Line Items]
Reinsurance assumed	10,650	12,765	13,639
Discontinued Operations | Discontinued Operations - Life Insurance
Segment Reporting, Revenue Reconciling Item [Line Items]
Other	48	58	388
Total net premiums earned from continuing operations	61,368	87,270	79,984
Discontinued Operations | Discontinued Operations - Life Insurance | Ordinary life (excluding universal life)
Segment Reporting, Revenue Reconciling Item [Line Items]
Net premiums earned	35,388	63,668	53,114
Discontinued Operations | Discontinued Operations - Life Insurance | Universal life policy fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Net premiums earned	13,145	11,577	12,834
Discontinued Operations | Discontinued Operations - Life Insurance | Immediate annuities with life contingencies
Segment Reporting, Revenue Reconciling Item [Line Items]
Net premiums earned	11,691	10,533	12,223
Discontinued Operations | Discontinued Operations - Life Insurance | Accident and health
Segment Reporting, Revenue Reconciling Item [Line Items]
Net premiums earned	$ 1,096	$ 1,434	$ 1,425