Fair Values of Financial Instruments (Fair Value by Balance Sheet Grouping) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
ASSETS
Securities held to maturity	$ 6,414,859	$ 6,082,330
Securities available for sale	2,821,367	2,624,953
Derivatives, index options	87,833	30,844
Carrying Values [Member]
ASSETS
Securities held to maturity	5,849,916	5,641,909
Securities available for sale	2,821,367	2,624,953
Cash and short-term investments	127,945	119,290
Mortgage loans	135,776	157,460
Policy loans	74,138	74,967
Other loans	14,691	16,287
Derivatives, index options	87,833	30,844
Life interest in Libbie Shearn Moody Trust	83	330
LIABILITIES
Deferred annuity contracts	6,840,702	6,606,886
Immediate annuity and supplemental contracts	503,147	506,982
Fair Values [Member]
ASSETS
Securities held to maturity	6,414,860	6,082,330
Securities available for sale	2,821,367	2,624,953
Cash and short-term investments	127,945	119,290
Mortgage loans	141,013	158,958
Policy loans	74,138	74,967
Other loans	14,903	16,780
Derivatives, index options	87,833	30,844
Life interest in Libbie Shearn Moody Trust	12,775	12,775
LIABILITIES
Deferred annuity contracts	6,466,991	6,273,379
Immediate annuity and supplemental contracts	$ 548,490	$ 521,122

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