Accumulated Other Comprehensive Income (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at beginning of period	$ 102,330		$ 87,150
Change in accumulated other comprehensive income before reclassifications	17,620	(33,667)	33,264	(24,249)
Reclassification adjustments from accumulated other comprehensive income	(545)	(2,063)	(1,009)	(2,059)
Balance at end of period	119,405		119,405
Net unrealized appreciation on investments [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at beginning of period	131,282		116,601
Change in accumulated other comprehensive income before reclassifications	17,620		33,264
Reclassification adjustments from accumulated other comprehensive income	(1,044)		(2,007)
Balance at end of period	147,858		147,858
Liability for underfunded employee benefit costs [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at beginning of period	(28,952)		(29,451)
Change in accumulated other comprehensive income before reclassifications	0		0
Reclassification adjustments from accumulated other comprehensive income	499		998
Balance at end of period	$ (28,453)		$ (28,453)