Accumulated Other Comprehensive Income (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at beginning of period	$ 104,610		$ 95,188
Change in accumulated other comprehensive income before reclassifications	(33,667)	5,780	(24,249)	14,257
Reclassification adjustments from accumulated other comprehensive income	(2,063)	613	(2,059)	(421)
Balance at end of period	68,880		68,880
Net unrealized appreciation on investments [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at beginning of period	152,710		144,096
Change in accumulated other comprehensive income before reclassifications	(33,667)		(24,249)
Reclassification adjustments from accumulated other comprehensive income	(2,870)		(3,674)
Balance at end of period	116,173		116,173
Liability for underfunded employee benefit costs [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at beginning of period	(48,100)		(48,908)
Change in accumulated other comprehensive income before reclassifications	0		0
Reclassification adjustments from accumulated other comprehensive income	807		1,615
Balance at end of period	$ (47,293)		$ (47,293)