Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from operating activities:
Net income	$ 350,255	$ 219,414	$ 189,871
Adjustments to reconcile net income to cash provided by (used in) operating activities:
Change in future policy benefits and other policy liabilities	306,122	256,520	242,957
Deferral of policy acquisition costs	(422,749)	(376,879)	(326,197)
Amortization of deferred policy acquisition costs	209,399	180,582	157,727
Deferred tax provision	(53,788)	44,316	38,292
Change in income taxes	(2,159)	27,601	5,862
Realized investment (gains) losses, including other-than-temporary impairments	(1,339)	(4,088)	1,738
Accretion and amortization of investments	(1,596)	(1,411)	(1,343)
Depreciation and amortization	13,551	14,595	10,998
Change in reinsurance recoverables	9,124	(72,880)	(49,966)
Change in agent balances, due premiums and other receivables	(18,331)	(20,069)	(11,379)
Trading securities sold, matured, or called (acquired), net	1,137	(2,051)	2,308
Share-based compensation	15,267	13,442	14,948
Change in other operating assets and liabilities, net	(16,369)	15,335	(11,565)
Net cash provided by (used in) operating activities	388,524	294,427	264,251
Available-for-sale investments sold, matured or called:
Fixed-maturity securities — sold	76,701	91,666	130,608
Fixed-maturity securities — matured or called	223,088	254,585	247,771
Equity securities	5,771	8,572	4,894
Available-for-sale investments acquired:
Fixed-maturity securities	(426,689)	(386,394)	(433,457)
Equity securities	(400)	(2,683)	(882)
Purchases of property and equipment and other investing activities, net	(6,752)	(13,669)	(7,399)
Cash collateral received (returned) on loaned securities, net	16,140	2,164	21,271
Sales (purchases) of short-term investments using securities lending collateral, net	(16,140)	(2,164)	(21,271)
Net cash provided by (used in) investing activities	(128,281)	(47,923)	(58,465)
Cash flows from financing activities:
Dividends paid	(35,821)	(33,367)	(32,807)
Common stock repurchased	(150,038)	(150,057)	(200,084)
Tax withholdings on share-based compensation	(6,734)	(3,970)	(7,675)
Cash proceeds from stock options exercised			136
Payment of deferred financing costs	(868)
Net cash provided by (used in) financing activities	(193,461)	(187,394)	(240,430)
Effect of foreign exchange rate changes on cash	1,204	572	(5,059)
Change in cash and cash equivalents	67,986	59,682	(39,703)
Cash and cash equivalents, beginning of period	211,976	152,294	191,997
Cash and cash equivalents, end of period	279,962	211,976	152,294
Supplemental disclosures of cash flow information:
Income taxes paid	83,304	45,402	62,116
Interest paid	$ 27,816	$ 27,992	$ 32,386