CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues
Insurance premiums and contract charges earned	$ 794,703	$ 759,146	$ 731,880
Net investment income	373,630	361,186	332,600
Net realized investment gains (losses)	(3,406)	4,123	12,713
Other income	6,623	4,455	3,255
Total revenues	1,171,550	1,128,910	1,080,448
Benefits, losses and expenses
Benefits, claims and settlement expenses	582,306	541,004	496,364
Interest credited	198,635	192,022	182,842
DAC amortization expense	102,185	96,732	98,919
Operating expenses	187,789	173,112	157,411
Interest expense	11,948	11,808	13,122
Debt retirement costs	0	0	2,338
Total benefits, losses and expenses	1,082,863	1,014,678	950,996
Income before income taxes	88,687	114,232	129,452
Income tax expense (benefit)	(80,772)	30,467	35,970
Net income	$ 169,459	$ 83,765	$ 93,482
Net income per share
Basic (in usd per share)	$ 4.10	$ 2.04	$ 2.23
Diluted (in usd per share)	$ 4.08	$ 2.02	$ 2.20
Weighted average number of shares and equivalent shares
Basic (in shares)	41,364,546	41,158,349	41,914,864
Diluted (in shares)	41,564,979	41,475,516	42,424,806
Net realized investment gains (losses)
Total other-than-temporary impairment losses on securities	$ (12,620)	$ (11,401)	$ (23,796)
Portion of losses recognized in other comprehensive income (loss)	0	(290)	(4,300)
Net other-than-temporary impairment losses on securities recognized in earnings	(12,620)	(11,111)	(19,496)
Realized gains, net	9,214	15,234	32,209
Total	$ (3,406)	$ 4,123	$ 12,713