Fair Values of Financial Instruments (Fair Values and Carrying Amounts of Financial Instruments) (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Assets
Held for investment	$ 75,547	$ 65,377
Other investments	297,068	291,530
Coinsurance deposits	4,453,320	3,187,470
Liabilities
Policy benefit reserves	50,814,665	45,495,431
Carrying Amount [Member]
Assets
Mortgage loans on real estate	2,419,230	2,435,257
Derivative instruments	706,007	337,256
Other investments	297,068	285,044
Cash and cash equivalents	812,814	397,749
Coinsurance deposits	4,453,320	3,187,470
Counterparty collateral	144,082	82,312
Liabilities
Policy benefit reserves	50,461,717	45,151,460
Single premium immediate annuity (SPIA) benefit reserves	302,428	324,264
Notes and loan payable	493,445	393,227
Subordinated debentures	241,751	241,452
Carrying Amount [Member] | Interest Rate Caps [Member]
Assets
Interest rate derivative assets	307	1,410
Carrying Amount [Member] | Interest Rate Swap [Member]
Liabilities
Interest rate derivative liabilities	4,944	3,139
Carrying Amount [Member] | Fixed Maturity Securities [Member]
Assets
Available for sale securities	42,304,410	36,421,839
Held for investment	76,773	76,622
Carrying Amount [Member] | Equity Securities [Member]
Assets
Available for sale securities	7,843	7,828
Fair Value [Member]
Assets
Mortgage loans on real estate	2,446,247	2,471,864
Derivative instruments	706,007	337,256
Other investments	290,719	290,075
Cash and cash equivalents	812,814	397,749
Coinsurance deposits	3,997,317	2,860,882
Counterparty collateral	144,082	82,312
Liabilities
Policy benefit reserves	42,237,613	38,435,515
Single premium immediate annuity (SPIA) benefit reserves	313,130	336,066
Notes and loan payable	520,800	417,752
Subordinated debentures	227,755	216,933
Fair Value [Member] | Interest Rate Caps [Member]
Assets
Interest rate derivative assets	307	1,410
Fair Value [Member] | Interest Rate Swap [Member]
Liabilities
Interest rate derivative liabilities	4,944	3,139
Fair Value [Member] | Fixed Maturity Securities [Member]
Assets
Available for sale securities	42,304,410	36,421,839
Held for investment	75,547	65,377
Fair Value [Member] | Equity Securities [Member]
Assets
Available for sale securities	$ 7,843	$ 7,828