Fair Values of Financial Instruments (Fair Value by Balance Sheet Grouping) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
ASSETS
Securities held to maturity	$ 6,574,186	$ 6,503,627
Securities available for sale	2,752,530	2,826,001
Derivatives, index options	119,276	57,890
Carrying Values [Member]
ASSETS
Securities held to maturity	6,345,116	5,962,120
Securities available for sale	2,752,530	2,826,001
Cash and short-term investments	94,458	124,561
Mortgage loans	117,091	142,170
Policy loans	68,307	71,549
Other loans	3,185	14,997
Derivatives, index options	119,276	57,890
Life interest in Libbie Shearn Moody Trust	0	0
LIABILITIES
Deferred annuity contracts	7,154,103	6,907,055
Immediate annuity and supplemental contracts	471,825	492,853
Fair Values [Member]
ASSETS
Securities held to maturity	6,574,186	6,503,627
Securities available for sale	2,752,530	2,826,001
Cash and short-term investments	94,458	124,561
Mortgage loans	122,782	147,365
Policy loans	68,307	71,549
Other loans	3,360	15,273
Derivatives, index options	119,276	57,890
Life interest in Libbie Shearn Moody Trust	12,775	12,775
LIABILITIES
Deferred annuity contracts	6,876,234	6,624,111
Immediate annuity and supplemental contracts	$ 498,502	$ 531,857