Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at beginning of period	$ 99,679		$ 91,173
Change in accumulated other comprehensive income before reclassifications	(23,555)	$ 17,620	(15,031)	$ 33,264
Reclassification adjustments from accumulated other comprehensive income (loss)	567	$ (545)	549	$ (1,009)
Balance at end of period	76,691		76,691
Net unrealized appreciation on investments [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at beginning of period	156,915		149,623
Change in accumulated other comprehensive income before reclassifications	(23,555)		(15,031)
Reclassification adjustments from accumulated other comprehensive income (loss)	(646)		(1,878)
Balance at end of period	132,714		132,714
Liability for underfunded employee benefit costs [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at beginning of period	(57,236)		(58,450)
Change in accumulated other comprehensive income before reclassifications	0		0
Reclassification adjustments from accumulated other comprehensive income (loss)	1,213		2,427
Balance at end of period	$ (56,023)		$ (56,023)