Comprehensive Income (Reclassification out of AOCI) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Net realized gains (losses)	$ 1,765	$ (3,420)	$ (939)	$ 15,463
Net investment income	31,182	32,230	61,951	59,147
Loss and loss expense incurred	298,479	291,561	595,623	576,560
Policy acquisition costs	190,731	169,770	373,958	334,493
Income before federal income tax	62,311	46,765	114,186	103,055
Total federal income tax expense	(18,710)	(12,997)	(33,553)	(29,579)
Net income (loss)	43,601	33,768	80,633	73,476
Reclassification out of AOCI
Net income (loss)	(172)	3,216	2,521	(8,543)
Reclassification out of AOCI | Non-credit OTTI on Disposed Securities [Member]
Net realized gains (losses)	0	0	0	357
Income before federal income tax	0	0	0	357
Total federal income tax expense	0	0	0	(125)
Net income (loss)	0	0	0	232
Reclassification out of AOCI | Held-to-maturity Securities [Member]
Net realized gains (losses)	60	87	88	137
Net investment income	(79)	(272)	(179)	(583)
Income before federal income tax	(19)	(185)	(91)	(446)
Total federal income tax expense	7	65	32	156
Net income (loss)	(12)	(120)	(59)	(290)
Reclassification out of AOCI | Available-for-sale Securities [Member]
Net realized gains (losses)	(1,762)	3,422	937	(16,473)
Income before federal income tax	(1,762)	3,422	937	(16,473)
Total federal income tax expense	617	(1,197)	(328)	5,766
Net income (loss)	(1,145)	2,225	609	(10,707)
Pension Plan [Member] | Reclassification out of AOCI
Loss and loss expense incurred	329	372	658	743
Policy acquisition costs	1,188	1,337	2,375	2,675
Income before federal income tax	1,517	1,709	3,033	3,418
Total federal income tax expense	(532)	(598)	(1,062)	(1,196)
Net income (loss)	$ 985	$ 1,111	$ 1,971	$ 2,222