SEGMENT INFORMATION (Net Premiums) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting, Revenue Reconciling Item [Line Items]
Total net premiums earned from continuing operations	$ 1,055,082	$ 1,086,972	$ 1,037,451
Property and casualty business
Segment Reporting, Revenue Reconciling Item [Line Items]
Reinsurance assumed	33,679	25,412	16,957
Other	2,678	2,942	2,938
Total net premiums earned from continuing operations	1,055,082	1,086,972	1,037,451
Property and casualty business | Other liability
Segment Reporting, Revenue Reconciling Item [Line Items]
Net premiums earned	316,098	318,412	311,931
Property and casualty business | Fire and allied lines
Segment Reporting, Revenue Reconciling Item [Line Items]
Net premiums earned	277,515	285,205	276,193
Property and casualty business | Automobile
Segment Reporting, Revenue Reconciling Item [Line Items]
Net premiums earned	324,420	345,637	313,521
Property and casualty business | Workers' compensation
Segment Reporting, Revenue Reconciling Item [Line Items]
Net premiums earned	75,953	87,376	95,203
Property and casualty business | Fidelity and surety
Segment Reporting, Revenue Reconciling Item [Line Items]
Net premiums earned	28,001	25,539	24,437
Property and casualty business | Reinsurance assumed
Segment Reporting, Revenue Reconciling Item [Line Items]
Reinsurance assumed	30,417	21,861	13,228
Life Insurance | Discontinued Operations
Segment Reporting, Revenue Reconciling Item [Line Items]
Other	0	0	12
Total net premiums earned from continuing operations	0	0	13,003
Life Insurance | Discontinued Operations | Ordinary life (excluding universal life)
Segment Reporting, Revenue Reconciling Item [Line Items]
Net premiums earned	0	0	7,068
Life Insurance | Discontinued Operations | Universal life policy fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Net premiums earned	0	0	3,363
Life Insurance | Discontinued Operations | Immediate annuities with life contingencies
Segment Reporting, Revenue Reconciling Item [Line Items]
Net premiums earned	0	0	2,515
Life Insurance | Discontinued Operations | Accident and health
Segment Reporting, Revenue Reconciling Item [Line Items]
Net premiums earned	$ 0	$ 0	$ 45