Fair Values of Financial Instruments (Fair Value by Balance Sheet Grouping) (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
ASSETS
Securities held to maturity	$ 6,245,687	$ 6,082,330
Securities available for sale	2,754,759	2,624,953
Derivatives, index options	65,555	30,844
Carrying Values [Member]
ASSETS
Securities held to maturity	5,738,777	5,641,909
Securities available for sale	2,754,759	2,624,953
Cash and short-term investments	111,264	119,290
Mortgage loans	132,614	157,460
Policy loans	74,369	74,967
Other loans	14,150	16,287
Derivatives, index options	65,555	30,844
Life interest in Libbie Shearn Moody Trust	165	330
LIABILITIES
Deferred annuity contracts	6,716,796	6,606,886
Immediate annuity and supplemental contracts	510,974	506,982
Fair Values [Member]
ASSETS
Securities held to maturity	6,245,687	6,082,330
Securities available for sale	2,754,759	2,624,953
Cash and short-term investments	111,264	119,290
Mortgage loans	138,556	158,958
Policy loans	74,223	74,967
Other loans	14,350	16,780
Derivatives, index options	65,555	30,844
Life interest in Libbie Shearn Moody Trust	12,775	12,775
LIABILITIES
Deferred annuity contracts	6,356,967	6,273,379
Immediate annuity and supplemental contracts	$ 544,078	$ 521,122

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