Fair Value of Assets and Liabilities Fair Value of Assets and Liabilities (Financial Instruments where Carrying Amounts and Fair Values May Differ) (Details) - USD ($) $ in Thousands		Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018	Dec. 31, 2017
Assets
Mortgage loans on real estate (net of valuation allowances)		$ 5,647,265	$ 4,966,298
Policy loans		1,289,868	1,344,980
Funds withheld at interest		5,614,363	5,761,471
Cash and cash equivalents		2,635,596	1,889,733	$ 1,730,489	$ 1,303,524
Short-term investments		107,503	142,598
Other invested assets		2,215,275	1,915,297
Accrued investment income		520,301	427,893
Liabilities
Interest-sensitive contract liabilities		22,345,126	18,004,526
Long-term debt		3,381,406	2,787,873
Collateral finance and securitization notes		610,246	681,961
Reported Value Measurement [Member]
Assets
Mortgage loans on real estate (net of valuation allowances)	[1]	5,647,265	4,966,298
Policy loans	[1]	1,289,868	1,344,980
Funds withheld at interest	[1]	5,476,148	5,655,055
Cash and cash equivalents	[1]	1,708,421	1,404,566
Short-term investments	[1]	18,373	36,607
Other invested assets	[1]	1,147,167	945,731
Accrued investment income	[1]	520,301	427,893
Liabilities
Interest-sensitive contract liabilities	[1]	18,747,630	14,547,436
Long-term debt	[1]	3,381,406
Debt, Long-term and Short-term, Combined Amount	[1]		2,787,873
Collateral finance and securitization notes	[1]	610,246	681,961
Estimate of Fair Value Measurement [Member]
Assets
Mortgage loans on real estate (net of valuation allowances)		5,936,051	4,917,416
Policy loans		1,289,868	1,344,980
Funds withheld at interest		5,873,575	5,802,518
Cash and cash equivalents		1,708,421	1,404,566
Short-term investments		18,373	36,607
Other invested assets		1,205,284	941,449
Accrued investment income		520,301	427,893
Liabilities
Interest-sensitive contract liabilities		20,446,240	14,611,011
Long-term Debt, Fair Value		3,564,595
Debt, Long-term and Short-term, Combined Amount			2,752,047
Collateral finance and securitization notes		561,011	626,731
Estimate of Fair Value Measurement [Member] | Fair Value Inputs Level 1 Member
Assets
Mortgage loans on real estate (net of valuation allowances)		0	0
Policy loans		0	0
Funds withheld at interest		0	0
Cash and cash equivalents		1,708,421	1,404,566
Short-term investments		18,373	36,607
Other invested assets		5,208	4,640
Accrued investment income		0	0
Liabilities
Interest-sensitive contract liabilities		0	0
Long-term Debt, Fair Value		0
Debt, Long-term and Short-term, Combined Amount			0
Collateral finance and securitization notes		0	0
Estimate of Fair Value Measurement [Member] | Fair Value Inputs Level 2 Member
Assets
Mortgage loans on real estate (net of valuation allowances)		0	0
Policy loans		1,289,868	1,344,980
Funds withheld at interest		0	0
Cash and cash equivalents		0	0
Short-term investments		0	0
Other invested assets		82,360	83,203
Accrued investment income		520,301	427,893
Liabilities
Interest-sensitive contract liabilities		0	0
Long-term Debt, Fair Value		0
Debt, Long-term and Short-term, Combined Amount			0
Collateral finance and securitization notes		0	0
Estimate of Fair Value Measurement [Member] | Fair Value Inputs Level 3 Member
Assets
Mortgage loans on real estate (net of valuation allowances)		5,936,051	4,917,416
Policy loans		0	0
Funds withheld at interest		5,873,575	5,802,518
Cash and cash equivalents		0	0
Short-term investments		0	0
Other invested assets		737,064	477,214
Accrued investment income		0	0
Liabilities
Interest-sensitive contract liabilities		20,446,240	14,611,011
Long-term Debt, Fair Value		3,564,595
Debt, Long-term and Short-term, Combined Amount			2,752,047
Collateral finance and securitization notes		561,011	626,731
Estimate of Fair Value Measurement [Member] | Fair Value Measured at Net Asset Value Per Share [Member]
Assets
Mortgage loans on real estate (net of valuation allowances)		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		380,652	376,392
Accrued investment income		0	0
Liabilities
Interest-sensitive contract liabilities		0	0
Long-term Debt, Fair Value		0
Debt, Long-term and Short-term, Combined Amount			0
Collateral finance and securitization notes		$ 0	$ 0

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