ACCUMULATED OTHER COMPREHENSIVE INCOME (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Increase (Decrease) in Accumulated Other Comprehensive Income [Roll Forward]
Balance as of beginning of period	$ 91,173	$ 87,150	$ 95,188
Change in accumulated other comprehensive income before reclassifications	(12,657)	5,332	(7,425)
Reclassification adjustments from accumulated other comprehensive income	1,921	(1,309)	(613)
Balance as of end of period	80,437	91,173	87,150
Net Unrealized Appreciation on Investments [Member]
Increase (Decrease) in Accumulated Other Comprehensive Income [Roll Forward]
Balance as of beginning of period	149,623	116,601	144,096
Change in accumulated other comprehensive income before reclassifications	(18,321)	36,328	(23,068)
Reclassification adjustments from accumulated other comprehensive income	(2,933)	(3,306)	(4,427)
Balance as of end of period	128,369	149,623	116,601
Liability for Underfunded Employee Benefit Costs [Member]
Increase (Decrease) in Accumulated Other Comprehensive Income [Roll Forward]
Balance as of beginning of period	(58,450)	(29,451)	(48,908)
Change in accumulated other comprehensive income before reclassifications	5,664	(30,996)	15,643
Reclassification adjustments from accumulated other comprehensive income	4,854	1,997	3,814
Balance as of end of period	$ (47,932)	$ (58,450)	$ (29,451)