ACCUMULATED OTHER COMPREHENSIVE INCOME (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Increase (Decrease) in Accumulated Other Comprehensive Income [Roll Forward]
Balance as of beginning of period	$ 87,150	$ 95,188	$ 82,586
Change in accumulated other comprehensive income before reclassifications	5,332	(7,425)	12,037
Reclassification adjustments from accumulated other comprehensive income	(1,309)	(613)	565
Balance as of end of period	91,173	87,150	95,188
Net Unrealized Appreciation on Investments [Member]
Increase (Decrease) in Accumulated Other Comprehensive Income [Roll Forward]
Balance as of beginning of period	116,601	144,096	124,376
Change in accumulated other comprehensive income before reclassifications	36,328	(23,068)	22,386
Reclassification adjustments from accumulated other comprehensive income	(3,306)	(4,427)	(2,666)
Balance as of end of period	149,623	116,601	144,096
Liability for Underfunded Employee Benefit Costs [Member]
Increase (Decrease) in Accumulated Other Comprehensive Income [Roll Forward]
Balance as of beginning of period	(29,451)	(48,908)	(41,790)
Change in accumulated other comprehensive income before reclassifications	(30,996)	15,643	(10,349)
Reclassification adjustments from accumulated other comprehensive income	1,997	3,814	3,231
Balance as of end of period	$ (58,450)	$ (29,451)	$ (48,908)