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		Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Assets
Mortgage loans on real estate (net of valuation allowances)		$ 5,117,545	$ 4,966,298
Policy loans		1,312,349	1,344,980
Funds withheld at interest		5,729,838	5,761,471
Cash and cash equivalents		2,020,396	1,889,733	$ 1,510,407	$ 1,303,524
Short-term investments		119,215	142,598
Other invested assets		2,006,870	1,915,297
Accrued investment income		442,956	427,893
Liabilities
Interest-sensitive contract liabilities		17,750,197	18,004,526
Long-term debt		2,787,717	2,787,873
Collateral finance and securitization notes		656,174	681,961
Reported Value Measurement [Member]
Assets
Mortgage loans on real estate (net of valuation allowances)	[1]	5,117,545	4,966,298
Policy loans	[1]	1,312,349	1,344,980
Funds withheld at interest	[1]	5,619,039	5,655,055
Cash and cash equivalents	[1]	1,165,131	1,404,566
Short-term investments	[1]	43,855	36,607
Other invested assets	[1]	1,061,220	945,731
Accrued investment income	[1]	442,956	427,893
Liabilities
Interest-sensitive contract liabilities	[1]	14,543,332	14,547,436
Long-term debt	[1]	2,787,717
Debt, Long-term and Short-term, Combined Amount	[1]		2,787,873
Collateral finance and securitization notes	[1]	656,174	681,961
Estimate of Fair Value Measurement [Member]
Assets
Mortgage loans on real estate (net of valuation allowances)		5,210,513	4,917,416
Policy loans		1,312,349	1,344,980
Funds withheld at interest		5,823,245	5,802,518
Cash and cash equivalents		1,165,131	1,404,566
Short-term investments		43,855	36,607
Other invested assets		1,060,931	941,449
Accrued investment income		442,956	427,893
Liabilities
Interest-sensitive contract liabilities		14,790,369	14,611,011
Long-term Debt, Fair Value		2,915,623
Debt, Long-term and Short-term, Combined Amount			2,752,047
Collateral finance and securitization notes		601,680	626,731
Estimate of Fair Value Measurement [Member] | Net Asset Value [Member]
Assets
Mortgage loans on real estate (net of valuation allowances)			0
Policy loans			0
Funds withheld at interest			0
Cash and cash equivalents			0
Short-term investments			0
Other invested assets		368,391	376,392
Accrued investment income			0
Liabilities
Interest-sensitive contract liabilities			0
Debt, Long-term and Short-term, Combined Amount			0
Collateral finance and securitization notes			0
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		1,165,131	1,404,566
Short-term investments		43,855	36,607
Other invested assets		5,176	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		1,312,349	1,344,980
Funds withheld at interest		0	0
Cash and cash equivalents		0	0
Short-term investments		0	0
Other invested assets		83,529	83,203
Accrued investment income		442,956	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)		5,210,513	4,917,416
Policy loans		0	0
Funds withheld at interest		5,823,245	5,802,518
Cash and cash equivalents		0	0
Short-term investments		0	0
Other invested assets		603,835	477,214
Accrued investment income		0	0
Liabilities
Interest-sensitive contract liabilities		14,790,369	14,611,011
Long-term Debt, Fair Value		2,915,623
Debt, Long-term and Short-term, Combined Amount			2,752,047
Collateral finance and securitization notes		601,680	$ 626,731
Estimate of Fair Value Measurement [Member] | Fair Value Inputs Level 3 Member | Net Asset Value [Member]
Assets
Mortgage loans on real estate (net of valuation allowances)		0
Policy loans		0
Funds withheld at interest		0
Cash and cash equivalents		0
Short-term investments		0
Accrued investment income		0
Liabilities
Interest-sensitive contract liabilities		0
Long-term Debt, Fair Value		0
Collateral finance and securitization notes		$ 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.