Fair Values of Financial Instruments (Fair Value by Balance Sheet Grouping) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total	$ 6,503,627	$ 6,082,330
Securities available for sale	2,826,001	2,624,953
Derivatives, index options	57,890	30,844
Carrying Values [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total	5,962,120	5,641,909
Securities available for sale	2,826,001	2,624,953
Cash and short-term investments	124,561	119,290
Mortgage loans	142,170	157,460
Policy loans	71,549	74,967
Other loans	14,997	16,287
Derivatives, index options	57,890	30,844
Life interest in Libbie Shearn Moody Trust	0	330
Deferred annuity contracts	6,907,055	6,606,886
Immediate annuity and supplemental contracts	492,853	506,982
Fair Values [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total	6,503,627	6,082,330
Securities available for sale	2,826,001	2,624,953
Cash and short-term investments	124,561	119,290
Mortgage loans	147,365	158,958
Policy loans	71,549	74,967
Other loans	15,273	16,780
Derivatives, index options	57,890	30,844
Life interest in Libbie Shearn Moody Trust	12,775	12,775
Deferred annuity contracts	6,624,111	6,273,379
Immediate annuity and supplemental contracts	$ 531,857	$ 521,122

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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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