FEDERAL INCOME TAX (Net Deferred Tax Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Deferred tax liabilities
Deferred policy acquisition costs	$ 52,031	$ 53,960
Prepaid pension cost	4,449	1,920
Net bond discount accretion	1,134	1,430
Depreciation	854	1,791
Revaluation of investment basis	1,342	1,824
Identifiable intangible assets	3,311	3,560
Other	10,943	7,627
Gross deferred tax liability	148,415	141,945
Deferred tax assets
Financial statement reserves in excess of income tax reserves	29,174	34,535
Unearned premium adjustment	30,697	28,679
Net operating loss carryforwards	718	1,265
Underfunded benefit plan obligation	13,374	25,810
Post-retirement benefits other than pensions	20,221	17,838
Other-than-temporary impairment of investments	4,658	5,609
Contingent ceding commission accrual	2,769	3,342
Compensation expense related to stock options	4,578	4,627
Other	7,356	6,852
Gross deferred tax asset	113,545	128,557
Valuation allowance	(718)	(1,265)
Deferred tax asset	112,827	127,292
Net deferred tax liability	35,588	14,653
Equity securities
Deferred tax liabilities
Net unrealized appreciation on investment securities	70,640	58,674
All other securities
Deferred tax liabilities
Net unrealized appreciation on investment securities	$ 3,711	$ 11,159