Fair Values of Financial Instruments (Fair Values and Carrying Amounts of Financial Instruments) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Assets
Held for investment	$ 71,499	$ 60,840
Equity securities, available for sale	7,756	7,778
Mortgage loans on real estate	2,474,306	2,581,082
Other investments	283,924	215,042
Coinsurance deposits	3,080,282	2,999,618
Liabilities
Policy benefit reserves	38,790,456	35,789,655
Carrying Amount [Member]
Assets
Mortgage loans on real estate	2,474,306	2,581,082
Derivative instruments	744,033	856,050
Other investments	261,590	192,198
Cash and cash equivalents	788,800	897,529
Coinsurance deposits	3,080,282	2,999,618
Counterparty collateral	198,434	315,824
Liabilities
Policy benefit reserves	38,453,572	35,453,166
Single premium immediate annuity (SPIA) benefit reserves	376,980	417,625
Notes payable	475,295	549,958
Subordinated debentures	246,193	246,050
Amounts due under repurchase agreements	81,189	0
Carrying Amount [Member] | Interest Rate Caps [Member]
Assets
Derivative assets	3,644	6,103
Carrying Amount [Member] | Interest Rate Swap [Member]
Assets
Derivative assets	0	712
Liabilities
Interest rate swap	1,252	0
Carrying Amount [Member] | 2015 Notes Hedges [Member]
Assets
2015 notes hedges	39,061	107,041
Carrying Amount [Member] | 2015 Notes Embedded Conversion Derivative [Member]
Liabilities
2015 notes embedded conversion derivative	39,061	107,041
Carrying Amount [Member] | Fixed Maturity Securities [Member]
Assets
Available for sale securities	31,023,646	26,610,447
Held for investment	76,387	76,255
Carrying Amount [Member] | Equity Securities [Member]
Assets
Equity securities, available for sale	7,756	7,778
Fair Value [Member]
Assets
Mortgage loans on real estate	2,536,716	2,615,410
Derivative instruments	744,033	856,050
Other investments	267,414	193,343
Cash and cash equivalents	788,800	897,529
Coinsurance deposits	2,733,971	2,669,432
Counterparty collateral	198,434	315,824
Liabilities
Policy benefit reserves	32,240,023	29,670,827
Single premium immediate annuity (SPIA) benefit reserves	389,508	430,835
Notes payable	546,548	699,435
Subordinated debentures	238,530	234,959
Amounts due under repurchase agreements	81,189	0
Fair Value [Member] | Interest Rate Caps [Member]
Assets
Derivative assets	3,644	6,103
Fair Value [Member] | Interest Rate Swap [Member]
Assets
Derivative assets	0	712
Liabilities
Interest rate swap	1,252	0
Fair Value [Member] | 2015 Notes Hedges [Member]
Assets
2015 notes hedges	39,061	107,041
Fair Value [Member] | 2015 Notes Embedded Conversion Derivative [Member]
Liabilities
2015 notes embedded conversion derivative	39,061	107,041
Fair Value [Member] | Fixed Maturity Securities [Member]
Assets
Available for sale securities	31,023,646	26,610,447
Held for investment	71,499	60,840
Fair Value [Member] | Equity Securities [Member]
Assets
Equity securities, available for sale	$ 7,756	$ 7,778