SEGMENT INFORMATION (Net Premiums) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting, Revenue Reconciling Item [Line Items]
Total net premiums earned from continuing operations	$ 1,086,972	$ 1,037,451	$ 997,492
Continuing Operations - Property and Casualty Insurance
Segment Reporting, Revenue Reconciling Item [Line Items]
Reinsurance assumed	25,412	16,957	15,059
Other	2,942	2,938	2,988
Total net premiums earned from continuing operations	1,086,972	1,037,451	997,492
Continuing Operations - Property and Casualty Insurance | Other liability
Segment Reporting, Revenue Reconciling Item [Line Items]
Net premiums earned	318,412	311,931	306,480
Continuing Operations - Property and Casualty Insurance | Fire and allied lines
Segment Reporting, Revenue Reconciling Item [Line Items]
Net premiums earned	285,205	276,193	270,716
Continuing Operations - Property and Casualty Insurance | Automobile
Segment Reporting, Revenue Reconciling Item [Line Items]
Net premiums earned	345,637	313,521	277,511
Continuing Operations - Property and Casualty Insurance | Workers' compensation
Segment Reporting, Revenue Reconciling Item [Line Items]
Net premiums earned	87,376	95,203	104,166
Continuing Operations - Property and Casualty Insurance | Fidelity and surety
Segment Reporting, Revenue Reconciling Item [Line Items]
Net premiums earned	25,539	24,437	24,981
Continuing Operations - Property and Casualty Insurance | Reinsurance assumed
Segment Reporting, Revenue Reconciling Item [Line Items]
Reinsurance assumed	21,861	13,228	10,650
Discontinued Operations | Discontinued Operations - Life Insurance
Segment Reporting, Revenue Reconciling Item [Line Items]
Other	0	12	48
Total net premiums earned from continuing operations	0	13,003	61,368
Discontinued Operations | Discontinued Operations - Life Insurance | Ordinary life (excluding universal life)
Segment Reporting, Revenue Reconciling Item [Line Items]
Net premiums earned	0	7,068	35,388
Discontinued Operations | Discontinued Operations - Life Insurance | Universal life policy fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Net premiums earned	0	3,363	13,145
Discontinued Operations | Discontinued Operations - Life Insurance | Immediate annuities with life contingencies
Segment Reporting, Revenue Reconciling Item [Line Items]
Net premiums earned	0	2,515	11,691
Discontinued Operations | Discontinued Operations - Life Insurance | Accident and health
Segment Reporting, Revenue Reconciling Item [Line Items]
Net premiums earned	$ 0	$ 45	$ 1,096