Fair Value of Assets and Liabilities (Financial Instruments where Carrying Amounts and Fair Values May Differ) (Details) - USD ($) $ in Thousands		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Mortgage loans on real estate		$ 4,966,298	$ 4,400,533
Policy loans		1,344,980	1,357,624
Funds withheld at interest		5,761,471	6,083,388
Cash and cash equivalents		1,889,733	1,303,524	$ 1,200,718	$ 1,525,275
Short-term investments		142,598	93,304
Other invested assets		1,915,297	1,505,332
Accrued investment income		427,893	392,721
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Interest-sensitive contract liabilities		18,004,526	16,227,642
Collateral finance and securitization notes		681,961	783,938
Carrying Value [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Mortgage loans on real estate	[1]	4,966,298	4,400,533
Policy loans	[1]	1,344,980	1,357,624
Funds withheld at interest	[1]	5,655,055	5,955,092
Cash and cash equivalents	[1]	1,404,566	946,736
Short-term investments	[1]	36,607	42,558
Other invested assets	[1]	945,731	690,198
Accrued investment income	[1]	427,893	392,721
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Interest-sensitive contract liabilities	[1]	14,547,436	12,683,872
Long And Short Term Debt	[1]	2,787,873	2,788,365
Collateral finance and securitization notes	[1]	681,961	783,938
Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Mortgage loans on real estate		4,917,416	4,477,654
Policy loans		1,344,980	1,357,624
Funds withheld at interest		5,802,518	6,275,623
Cash and cash equivalents		1,404,566	946,736
Short-term investments		36,607	42,558
Other invested assets		941,449	718,282
Accrued investment income		427,893	392,721
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Interest-sensitive contract liabilities		14,611,011	12,917,243
Long And Short Term Debt		2,752,047	2,959,912
Collateral finance and securitization notes		626,731	722,145
Estimate of Fair Value Measurement [Member] | Net Asset Value [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Mortgage loans on real estate		0	0
Policy loans		0	0
Funds withheld at interest		0	0
Cash and cash equivalents		0	0
Short-term investments		0	0
Other invested assets		376,392	335,125
Accrued investment income		0	0
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Interest-sensitive contract liabilities		0	0
Long And Short Term Debt		0	0
Collateral finance and securitization notes		0	0
Fair Value, Inputs, Level 1 [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Mortgage loans on real estate		0	0
Policy loans		0	0
Funds withheld at interest		0	0
Cash and cash equivalents		1,404,566	946,736
Short-term investments		36,607	42,558
Other invested assets		4,640	28,540
Accrued investment income		0	0
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Interest-sensitive contract liabilities		0	0
Long And Short Term Debt		0	0
Collateral finance and securitization notes		0	0
Fair Value, Inputs, Level 2 [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Mortgage loans on real estate		0	0
Policy loans		1,344,980	1,357,624
Funds withheld at interest		0	0
Cash and cash equivalents		0	0
Short-term investments		0	0
Other invested assets		83,203	67,778
Accrued investment income		427,893	392,721
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Interest-sensitive contract liabilities		0	0
Long And Short Term Debt		0	0
Collateral finance and securitization notes		0	0
Fair Value, Inputs, Level 3 [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Mortgage loans on real estate		4,917,416	4,477,654
Policy loans		0	0
Funds withheld at interest		5,802,518	6,275,623
Cash and cash equivalents		0	0
Short-term investments		0	0
Other invested assets		477,214	286,839
Accrued investment income		0	0
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Interest-sensitive contract liabilities		14,611,011	12,917,243
Long And Short Term Debt		2,752,047	2,959,912
Collateral finance and securitization notes		$ 626,731	$ 722,145

[1] Carrying values presented herein may differ from those in the Company’s consolidated balance sheets because certain items within the respective financial statement captions may be measured at fair value on a recurring basis.