Accumulated Other Comprehensive Income (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at beginning of period	$ 68,880		$ 95,188
Change in accumulated other comprehensive income before reclassifications	(175)	12,788	(24,424)	27,045
Reclassification adjustments from accumulated other comprehensive income	843	646	(1,216)	225
Balance at end of period	69,548		69,548
Net unrealized appreciation on investments [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at beginning of period	116,173		144,096
Change in accumulated other comprehensive income before reclassifications	(175)		(24,424)
Reclassification adjustments from accumulated other comprehensive income	(402)		(4,076)
Balance at end of period	115,596		115,596
Liability for underfunded employee benefit costs [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at beginning of period	(47,293)		(48,908)
Change in accumulated other comprehensive income before reclassifications	0		0
Reclassification adjustments from accumulated other comprehensive income	1,245		2,860
Balance at end of period	$ (46,048)		$ (46,048)