Fair Values of Financial Instruments (Fair Value by Balance Sheet Grouping) (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
ASSETS
Securities held to maturity	$ 7,370,596	$ 7,175,443
Securities available for sale	2,840,589	2,728,680
Derivatives, index options	72,527	114,287
Fair Values [Member]
ASSETS
Securities held to maturity	7,370,596	7,175,443
Securities available for sale	2,840,589	2,728,680
Cash and short-term investments	71,710	277,078
Mortgage loans	137,917	156,548
Policy loans	107,914	111,040
Other loans	2,773	2,300
Derivatives, index options	72,527	114,287
Life interest in Libbie Shearn Moody Trust	12,775	12,775
LIABILITIES
Deferred annuity contracts	7,215,118	7,178,535
Immediate annuity and supplemental contracts	467,034	474,843
Carrying Values [Member]
ASSETS
Securities held to maturity	7,121,439	6,841,543
Securities available for sale	2,840,589	2,728,680
Cash and short-term investments	71,710	277,078
Mortgage loans	132,261	149,503
Policy loans	61,933	63,645
Other loans	2,598	2,171
Derivatives, index options	72,527	114,287
Life interest in Libbie Shearn Moody Trust	0	0
LIABILITIES
Deferred annuity contracts	7,597,966	7,546,504
Immediate annuity and supplemental contracts	439,889	446,458
Level 1 [Member]
ASSETS
Securities held to maturity	0	0
Securities available for sale	16,533	16,862
Cash and short-term investments	71,710	277,078
Mortgage loans	0	0
Policy loans	0	0
Other loans	0	0
Derivatives, index options	0	0
Life interest in Libbie Shearn Moody Trust	0	0
LIABILITIES
Deferred annuity contracts	0	0
Immediate annuity and supplemental contracts	0	0
Level 2 [Member]
ASSETS
Securities held to maturity	7,370,596	7,175,443
Securities available for sale	2,824,056	2,711,818
Cash and short-term investments	0	0
Mortgage loans	0	0
Policy loans	0	0
Other loans	0	0
Derivatives, index options	0	0
Life interest in Libbie Shearn Moody Trust	0	0
LIABILITIES
Deferred annuity contracts	0	0
Immediate annuity and supplemental contracts	0	0
Level 3 [Member]
ASSETS
Securities held to maturity	0	0
Securities available for sale	0	0
Cash and short-term investments	0	0
Mortgage loans	137,917	156,548
Policy loans	107,914	111,040
Other loans	2,773	2,300
Derivatives, index options	72,527	114,287
Life interest in Libbie Shearn Moody Trust	12,775	12,775
LIABILITIES
Deferred annuity contracts	7,215,118	7,178,535
Immediate annuity and supplemental contracts	$ 467,034	$ 474,843