Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Statement of Cash Flows [Abstract]
Cash provided from operating activities	$ 460,756	$ 340,738
Investments sold or matured:
Fixed maturities available for sale—sold	0	14,331
Fixed maturities available for sale—matured, called, and repaid	108,899	44,622
Other long-term investments	3,071	8
Total long-term investments sold or matured	111,970	58,961
Acquisition of investments:
Fixed maturities—available for sale	(461,324)	(287,204)
Other long-term investments	0	(644)
Total investments acquired	(461,324)	(287,848)
Net increase in policy loans	(2,599)	(4,378)
Net (increase) decrease in short-term investments	(48,950)	(89,905)
Additions to property and equipment	(3,978)	(3,879)
Sale of other assets	18	0
Investment in low-income housing interests	(5,875)	(7,925)
Cash provided from (used for) investing activities	(410,738)	(334,974)
Cash provided from (used for) financing activities:
Issuance of common stock	22,225	3,763
Cash dividends paid to shareholders	(16,503)	(16,524)
Net borrowing (repayment) of commercial paper	61,919	66,899
Acquisition of treasury stock	(113,719)	(85,089)
Net receipts (payments) from deposit-type product	(21,174)	(17,641)
Cash provided from (used for) financing activities	(67,252)	(48,592)
Effect of foreign exchange rate changes on cash	2,825	(5,797)
Net increase (decrease) in cash	(14,409)	(48,625)
Cash at beginning of year	76,163	61,383
Cash at end of period	$ 61,754	$ 12,758