Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Statement of Cash Flows [Abstract]
Cash provided from operating activities	$ 1,085,842	$ 971,926
Investments sold or matured:
Fixed maturities available for sale—sold	52,951	75,299
Fixed maturities available for sale—matured, called, and repaid	306,132	178,873
Other long-term investments	3,523	466
Total long-term investments sold or matured	362,606	254,638
Acquisition of investments:
Fixed maturities—available for sale	(1,042,705)	(910,090)
Other long-term investments	(16,775)	(20,404)
Total investments acquired	(1,059,480)	(930,494)
Net increase in policy loans	(15,343)	(6,623)
Net (increase) decrease in short-term investments	6,556	(11,138)
Net change in payable or receivable for securities	0	94
Additions to property and equipment	(13,451)	(10,138)
Sale of other assets	18	767
Investment in low-income housing interests	(13,852)	(16,126)
Cash provided from (used for) investing activities	(732,946)	(719,020)
Cash provided from (used for) financing activities:
Issuance of common stock	40,891	47,053
Cash dividends paid to shareholders	(51,532)	(50,258)
Proceeds from issuance of debt	0	400,000
Payment for debt issuance costs	0	(9,638)
Repayment of debt	(1,250)	(250,000)
Net borrowing (repayment) of commercial paper	42,652	25,266
Acquisition of treasury stock	(301,448)	(311,356)
Net receipts (payments) from deposit-type product	(65,912)	(57,188)
Cash provided from (used for) financing activities	(336,599)	(206,121)
Effect of foreign exchange rate changes on cash	(3,998)	(3,268)
Net increase (decrease) in cash	12,299	43,517
Cash at beginning of year	76,163	61,383
Cash at end of period	$ 88,462	$ 104,900