FEDERAL INCOME TAX (Net Deferred Tax Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred tax liabilities
Deferred policy acquisition costs	$ 19,487	$ 30,404
Investments in partnerships	2,510	3,653
Prepaid pension cost	4,158	3,416
Net bond discount accretion	296	666
Depreciation	1,063	593
Revaluation of investment basis	419	545
Identifiable intangible assets	1,689	1,838
Other	1,639	1,934
Gross deferred tax liability	67,213	101,487
Deferred tax assets
Financial statement reserves in excess of income tax reserves	19,800	17,036
Unearned premium adjustment	20,406	19,389
Net operating loss carryforwards	0	329
Underfunded benefit plan obligation	5,622	12,375
Post-retirement benefits other than pensions	12,035	11,942
Other-than-temporary impairment of investments	2,094	2,313
Contingent ceding commission accrual	14	317
Alternative minimum tax credit carryforward	0	6,011
Compensation expense related to stock options	3,506	3,289
Other	4,648	4,145
Gross deferred tax asset	68,125	77,146
Valuation allowance	0	(329)
Deferred tax asset	68,125	76,817
Net deferred tax asset	(912)
Net deferred tax liability (asset)		24,670
Equity securities
Deferred tax liabilities
Net unrealized appreciation on investment securities	38,430	50,839
All other securities
Deferred tax liabilities
Net unrealized appreciation on investment securities	$ (2,478)	$ 7,599