SEGMENT INFORMATION (Net Premiums) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Segment Reporting, Revenue Reconciling Item [Line Items]
Total net premiums earned	$ 930,890	$ 828,330	$ 754,846
Property and Casualty Insurance Segment [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Reinsurance assumed	18,396	16,265	185,485
Other	3,179	3,735	2,635
Total net premiums earned	851,695	766,939	694,192
Property and Casualty Insurance Segment [Member] | Other Liability [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Net premiums earned	261,303	228,426	199,548
Property and Casualty Insurance Segment [Member] | Fire and Allied Lines [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Net premiums earned	246,450	226,086	208,030
Property and Casualty Insurance Segment [Member] | Automobile [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Net premiums earned	210,090	187,813	169,211
Property and Casualty Insurance Segment [Member] | Workers' Compensation [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Net premiums earned	95,672	88,522	81,616
Property and Casualty Insurance Segment [Member] | Fidelity and Surety [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Net premiums earned	21,362	19,212	18,746
Property and Casualty Insurance Segment [Member] | Reinsurance Assumed [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Reinsurance assumed	13,639	13,145	14,406
Life Insurance Segment [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Other	388	261	261
Total net premiums earned	79,984	61,921	61,146
Life Insurance Segment [Member] | Ordinary Life (Excluding Universal Life) [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Total net premiums earned	53,114	35,557	38,875
Life Insurance Segment [Member] | Universal Life Policy Fees [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Total net premiums earned	12,834	13,190	11,871
Life Insurance Segment [Member] | Immediate Annuities with Life Contingencies [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Total net premiums earned	12,223	11,639	8,837
Life Insurance Segment [Member] | Accident and Health [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Total net premiums earned	$ 1,425	$ 1,274	$ 1,302