Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash provided from (used for) operating activities:
Net income	$ 1,454,494	$ 549,779	$ 527,100
Adjustments to reconcile net income from continuing operations to cash provided from continuing operations:
Loss (Income) from discontinued operations, net of income taxes	3,769	(10,189)	(10,807)
Increase (decrease) in future policy benefits	687,407	645,844	631,202
Increase (decrease) in other policy benefits	31,784	24,668	14,609
Deferral of policy acquisition costs	(660,134)	(635,318)	(612,181)
Amortization of deferred policy acquisition costs	490,403	469,063	445,625
Change in current and deferred income taxes	(700,660)	152,210	103,558
Realized (gains) losses on sale of investments and properties	(23,611)	10,683	8,791
Other, net	67,933	20,079	13,985
Net cash provided from (used for) continuing operations	1,351,385	1,226,819	1,121,882
Net cash provided from (used for) discontinued operations	77,673	171,889	(1,832)
Cash provided from (used for) operating activities	1,429,058	1,398,708	1,120,050
Cash provided from (used for) investing activities:
Fixed maturities available for sale—sold	67,246	340,434	226,792
Fixed maturities available for sale—matured, called, and repaid	488,843	236,353	376,158
Other long-term investments	3,534	1,217	3,740
Total investments sold or matured	559,623	578,004	606,690
Acquisition of investments:
Fixed maturities—available for sale	(1,314,609)	(1,530,053)	(1,070,908)
Other long-term investments	(55,096)	(20,444)	(31,707)
Total investments acquired	(1,369,705)	(1,550,497)	(1,102,615)
Net (increase) decrease in policy loans	(21,554)	(15,513)	(20,353)
Net (increase) decrease in short-term investments	(55,031)	(17,274)	(38,884)
Additions to properties	(20,285)	(25,162)	(36,957)
Sale of other assets	18	90	0
Investments in low-income housing interests	(19,890)	(32,084)	(41,231)
Cash provided from (used for) investing activities	(926,824)	(1,062,436)	(633,350)
Cash provided from (used for) financing activities:
Issuance of common stock	61,215	61,329	35,958
Cash dividends paid to shareholders	(68,831)	(66,931)	(66,899)
Repayment of debt	(126,875)	(250,000)	0
Proceeds from issuance of debt	125,000	400,000	0
Payment for debt issuance costs	(1,661)	(9,638)	0
Net borrowing (repayment) of commercial paper	61,092	22,224	1,978
Excess tax benefit from stock option exercises	0	0	17,577
Acquisition of treasury stock	(412,989)	(404,784)	(418,526)
Net receipts (payments) from deposit-type product	(90,932)	(71,991)	(95,793)
Cash provided from (used for) financing activities	(453,981)	(319,791)	(525,705)
Effect of foreign exchange rate changes on cash	(5,853)	(1,701)	34,369
Increase (decrease) in cash	42,400	14,780	(4,636)
Cash at beginning of year	76,163	61,383	66,019
Cash at end of year	$ 118,563	$ 76,163	$ 61,383