Accumulated Other Comprehensive Income (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at beginning of period	$ 119,405		$ 87,150
Change in accumulated other comprehensive income before reclassifications	(8,066)	(175)	25,198	(24,424)
Reclassification adjustments from accumulated other comprehensive income (loss)	(141)	843	(1,150)	(1,216)
Balance at end of period	111,198		111,198
Net unrealized appreciation on investments [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at beginning of period	147,858		116,601
Change in accumulated other comprehensive income before reclassifications	(8,066)		25,198
Reclassification adjustments from accumulated other comprehensive income (loss)	(640)		(2,647)
Balance at end of period	139,152		139,152
Liability for underfunded employee benefit costs [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at beginning of period	(28,453)		(29,451)
Change in accumulated other comprehensive income before reclassifications	0		0
Reclassification adjustments from accumulated other comprehensive income (loss)	499		1,497
Balance at end of period	$ (27,954)		$ (27,954)