Accumulated Other Comprehensive Income (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at beginning of period	$ 91,173
Change in accumulated other comprehensive income before reclassifications	8,524	15,644
Reclassification adjustments from accumulated other comprehensive income (loss)	(18)	(464)
Balance at end of period	99,679
Net unrealized appreciation on investments [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at beginning of period	149,623
Change in accumulated other comprehensive income before reclassifications	8,524
Reclassification adjustments from accumulated other comprehensive income (loss)	(1,232)
Balance at end of period	156,915
Liability for underfunded employee benefit costs [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at beginning of period	(58,450)
Change in accumulated other comprehensive income before reclassifications	0
Reclassification adjustments from accumulated other comprehensive income (loss)	1,214
Balance at end of period	$ (57,236)