ACCUMULATED OTHER COMPREHENSIVE INCOME (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Increase (Decrease) in Accumulated Other Comprehensive Income [Roll Forward]
Balance as of beginning of period	$ 95,188	$ 82,586	$ 76,978
Change in accumulated other comprehensive income before reclassifications	(7,425)	12,037	8,727
Reclassification adjustments from accumulated other comprehensive income	(613)	565	(3,119)
Balance as of end of period	87,150	95,188	82,586
Net Unrealized Appreciation on Investments [Member]
Increase (Decrease) in Accumulated Other Comprehensive Income [Roll Forward]
Balance as of beginning of period	144,096	124,376	102,649
Change in accumulated other comprehensive income before reclassifications	(23,068)	22,386	26,517
Reclassification adjustments from accumulated other comprehensive income	(4,427)	(2,666)	(4,790)
Balance as of end of period	116,601	144,096	124,376
Liability for Underfunded Employee Benefit Costs [Member]
Increase (Decrease) in Accumulated Other Comprehensive Income [Roll Forward]
Balance as of beginning of period	(48,908)	(41,790)	(25,671)
Change in accumulated other comprehensive income before reclassifications	15,643	(10,349)	(17,790)
Reclassification adjustments from accumulated other comprehensive income	3,814	3,231	1,671
Balance as of end of period	$ (29,451)	$ (48,908)	$ (41,790)