CONSOLIDATED STATEMENTS OF OPERATIONS (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Revenues
Insurance premiums and contract charges earned	$ 715,760	$ 690,938	$ 670,527
Net investment income	329,815	313,610	306,003
Net realized investment gains	10,917	22,245	27,298
Other income	4,193	4,474	6,986
Total revenues	1,060,685	1,031,267	1,010,814
Benefits, losses and expenses
Benefits, claims and settlement expenses	468,426	448,317	448,250
Interest credited	176,139	169,893	163,565
Policy acquisition expenses amortized	93,817	84,643	79,519
Operating expenses	161,992	160,112	156,058
Interest expense	14,198	14,236	14,249
Total benefits, losses and expenses	914,572	877,201	861,641
Income before income taxes	146,113	154,066	149,173
Income tax expense	41,870	43,173	45,307
Net income	104,243	110,893	103,866
Net income per share
Basic	$ 2.50	$ 2.75	$ 2.63
Diluted	$ 2.47	$ 2.66	$ 2.51
Weighted average number of shares and equivalent shares
Basic	41,646,281	40,376,562	39,513,540
Diluted	42,230,559	41,633,240	41,388,368
Net realized investment gains
Total other-than-temporary impairment losses on securities	(6,385)	(1,532)	0
Portion of losses recognized in other comprehensive income (loss)	0	0	0
Net other-than-temporary impairment losses on securities recognized in earnings	(6,385)	(1,532)	0
Realized gains, net	17,302	23,777	27,298
Total	$ 10,917	$ 22,245	$ 27,298