CONSOLIDATED STATEMENTS OF CASH FLOWS $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Cash flows from operating activities
Net Income (Loss) Attributable to Parent	$ 1,822,181	$ 701,443	$ 502,166
Change in operating assets and liabilities:
Accrued investment income	(43,142)	(18,761)	(48,458)
Premiums receivable and other reinsurance balances	(346,737)	(156,836)	(313,882)
Deferred policy acquisition costs	154,234	31,024	(66,633)
Reinsurance ceded receivable balances	(124,056)	(53,221)	(11,740)
Future policy benefits, other policy claims and benefits, and other reinsurance balances	1,320,810	810,474	1,867,488
Deferred income taxes	(847,304)	293,777	148,996
Other assets and other liabilities, net	242,466	(98,675)	(55,345)
Amortization of net investment premiums, discounts and other	(105,382)	(93,952)	(77,303)
Depreciation, Depletion and Amortization	52,902	26,853	31,103
Investment related (gains) losses, net	(167,880)	(94,195)	164,750
Excess tax benefits from share-based payment arrangement	0	(162)	(2,963)
Other, net	24,216	117,949	(49,564)
Net cash provided by operating activities	1,982,308	1,465,718	2,088,615
Cash flows from investing activities
Sales of fixed maturity securities available-for-sale	7,308,608	4,584,828	5,461,687
Principal payments on mortgage loans on real estate	589,214	472,435	439,640
Proceeds from Sale of Available-for-sale Securities, Equity	207,347	434,518	81,319
Proceeds from Sale and Collection of Mortgage Notes Receivable	339,919	442,755	383,828
Proceeds from Collection of Policy Loans	114,586	88,840	21,322
Payments to Acquire Available-for-sale Securities	(8,941,293)	(7,414,647)	(5,874,309)
Payments to Acquire Available-for-sale Securities, Equity	(81,254)	(584,532)	(95,834)
Purchases of fixed maturity securities available-for-sale	(964,421)	(1,092,876)	(810,092)
Payments to Fund Policy Loans	(44,607)	(47,646)	(52,207)
Cash invested in funds withheld at interest	(22,557)	(32,597)	(339,062)
Purchase of businesses, net of cash acquired of $69,823	0	0	(145,235)
Payments to Acquire Property, Plant, and Equipment	(44,211)	(44,642)	(23,553)
Increase (Decrease) in Payables under Repurchase Agreements	0	0	(101,203)
Change in short-term investments	52,302	465,628	(470,002)
Change in other invested assets	(121,206)	(97,790)	91,960
Net cash used in investing activities	(1,607,573)	(2,825,726)	(1,431,741)
Cash flows from financing activities
Dividends to stockholders	(117,291)	(100,371)	(93,381)
Repayment of collateral finance and securitization notes	(68,429)	(64,571)	(19,732)
Proceeds from Issuance of Secured Debt	0	0	164,220
Proceeds from long-term debt issuance	0	799,984	0
Debt issuance costs	0	(8,766)	(4,748)
Principal payments of long-term debt	(302,582)	(2,479)	(2,380)
Purchases of treasury stock	(43,508)	(122,916)	(384,519)
Excess tax benefits from share-based payment arrangement	0	162	2,963
Exercise of stock options, net	7,292	15,321	11,151
Change in cash collateral for derivative positions and other arrangements	(65,422)	26,413	52,381
Deposits on universal life and other investment type policies and contracts	1,017,699	1,041,623	277,280
Withdrawals on universal life and other investment type policies and contracts	(752,381)	(529,011)	(711,517)
Net cash used in financing activities	(324,622)	1,055,389	(708,282)
Effect of exchange rate changes on cash	52,693	(19,938)	(68,986)
Change in cash and cash equivalents	102,806	(324,557)	(120,394)
Cash and cash equivalents, beginning of period	1,200,718	1,525,275	1,645,669
Cash and cash equivalents, end of period	1,303,524	1,200,718	1,525,275
Supplementary information:
Interest paid	173,471	156,727	148,124
Income taxes paid, net of refunds	37,098	61,085	41,577
Transfer to Investments	3,285,837	120,500	2,092,558
Capital Expenditures Incurred but Not yet Paid	0	0	253
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities	0	0	(3,894,940)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets	$ 0	$ 0	$ 4,040,175