Consolidated Statements of Income and Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Revenues
Net premiums earned	$ 930,890	$ 828,330	$ 754,846
Investment income, net of investment expenses	100,781	104,609	112,799
Net realized investment gains (losses)
Other-than-temporary impairment charges	(1,300)	0	(139)
All other net realized gains (includes reclassifications for net unrealized gains on available-for-sale securities of $4,513 in 2015; $5,085 in 2014; and $6,812 in 2013 previously included in accumulated other comprehensive income)	4,146	7,270	8,834
Total net realized investment gains	2,846	7,270	8,695
Other income	401	1,685	702
Total revenues	1,034,918	941,894	877,042
Benefits, losses and expenses
Losses and loss settlement expenses	549,088	536,243	458,814
Increase in liability for future policy benefits	50,945	36,623	37,625
Amortization of deferred policy acquisition costs	186,817	167,449	153,677
Other underwriting expenses (includes reclassifications for employee benefit costs of $7,468 in 2015; $3,072 in 2014; and $5,868 in 2013 previously included in accumulated other comprehensive income)	102,937	94,871	89,861
Interest on policyholders' accounts	23,680	30,245	35,163
Total benefits, losses and expenses	913,467	865,431	775,140
Income before income taxes	121,451	76,463	101,902
Federal income tax expense (includes reclassifications of $1,034 in 2015; ($704) in 2014; and ($331) in 2013 previously included in accumulated other comprehensive income)	32,325	17,326	25,762
Net income	89,126	59,137	76,140
Other comprehensive income (loss)
Change in net unrealized appreciation on investments	(28,185)	55,888	(35,489)
Change in liability for underfunded employee benefit plans	8,714	(47,685)	24,066
Other comprehensive income (loss), before tax and reclassification adjustments	(19,471)	8,203	(11,423)
Income tax effect	6,814	(2,871)	3,998
Other comprehensive income (loss), after tax, before reclassification adjustments	(12,657)	5,332	(7,425)
Reclassifications for unrealized net gains on available-for-sale securities	(4,513)	(5,085)	(6,812)
Reclassification adjustment for employee benefit costs included in expense	7,468	3,072	5,868
Total reclassification adjustments, before tax	2,955	(2,013)	(944)
Income tax effect	(1,034)	704	331
Total reclassification adjustments, after tax	1,921	(1,309)	(613)
Comprehensive income	$ 78,390	$ 63,160	$ 68,102
Weighted average common shares outstanding (in shares)	25,047,405	25,230,854	25,325,695
Basic earnings per common share (in usd per share)	$ 3.56	$ 2.34	$ 3.01
Diluted earnings per common share (in usd per share)	$ 3.53	$ 2.32	$ 2.98