Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Statement of Cash Flows [Abstract]
Cash provided from operating activities	$ 423,285	$ 382,389
Disposition of investments:
Fixed maturities available for sale—sold	34,997	0
Fixed maturities available for sale—matured or other redemptions	188,253	74,019
Total investments disposed	223,250	74,019
Acquisition of investments:
Fixed maturities—available for sale	(421,111)	(358,753)
Other long-term investments	(22,971)	(53,853)
Total investments acquired	(444,082)	(412,606)
Net (increase) decrease in policy loans	(5,390)	(2,854)
Net (increase) decrease in short-term investments	(62,471)	47,048
Additions to properties	(7,015)	(11,966)
Investment in low-income housing interests	(10,054)	(7,518)
Cash provided from (used for) investing activities	(305,762)	(313,877)
Cash provided from (used for) financing activities:
Issuance of common stock	11,592	13,569
Cash dividends paid to shareholders	(17,696)	(17,194)
Repayment of debt	(1,250)	(625)
Net borrowing (repayment) of commercial paper	(14,095)	36,464
Acquisition of treasury stock	(110,896)	(109,954)
Net receipts (payments) from deposit-type product	(37,136)	(25,603)
Cash provided from (used for) financing activities	(169,481)	(103,343)
Effect of foreign exchange rate changes on cash	(1,726)	4,883
Net increase (decrease) in cash	(53,684)	(29,948)
Cash at beginning of year	121,026	118,563
Cash at end of period	$ 67,342	$ 88,615