FEDERAL INCOME TAX (Net Deferred Tax Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Deferred tax liabilities
Deferred policy acquisition costs	$ 53,960	$ 44,271
Prepaid pension cost	1,920	2,973
Net bond discount accretion	1,430	1,925
Depreciation	1,791	2,667
Revaluation of investment basis	1,824	2,611
Identifiable intangible assets	3,560	3,808
Other	7,627	8,152
Gross deferred tax liability	141,945	151,667
Deferred tax assets
Financial statement reserves in excess of income tax reserves	34,535	35,800
Unearned premium adjustment	28,679	26,146
Net operating loss carryforwards	1,265	1,813
Underfunded benefit plan obligation	25,810	31,473
Postretirement benefits other than pensions	17,838	14,374
Other-than-temporary impairment of investments	5,609	5,222
Contingent ceding commission accrual	3,342	3,573
Compensation expense related to stock options	4,627	4,582
Other	6,852	4,738
Gross deferred tax asset	128,557	127,721
Valuation allowance	(1,265)	(1,813)
Deferred tax asset	127,292	125,908
Net deferred tax liability	14,653	25,759
Equity Securities [Member]
Deferred tax liabilities
Net unrealized appreciation on investment securities	58,674	60,952
All Other Securities [Member]
Deferred tax liabilities
Net unrealized appreciation on investment securities	$ 11,159	$ 24,308