Fair Values of Financial Instruments (Fair Value by Balance Sheet Grouping) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt securities held to maturity	$ 7,228,268	$ 7,434,104
Debt securities, available for sale	2,946,059	3,041,131
Securities available for sale		3,059,609
Derivatives, index options	14,684	194,731
Equity securities	17,491	18,478
Carrying Values
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt securities held to maturity	7,285,254	7,247,024
Debt securities, available for sale	2,946,059
Securities available for sale		3,059,609
Cash and cash equivalents	131,976	217,624
Mortgage loans	203,180	208,249
Policy loans	54,724	56,405
Other loans	12,272	5,431
Derivatives, index options	14,684	194,731
Equity securities	17,491
Life interest in Libbie Shearn Moody Trust	8,692	8,676
Deferred annuity contracts	7,455,642	7,865,786
Immediate annuity and supplemental contracts	407,413	430,494
Fair Values
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt securities held to maturity	7,228,268	7,434,104
Debt securities, available for sale	2,946,059
Securities available for sale		3,059,609
Cash and cash equivalents	131,976	217,624
Mortgage loans	202,762	208,815
Policy loans	90,802	100,230
Other loans	12,709	5,603
Derivatives, index options	14,684	194,731
Equity securities	17,491
Life interest in Libbie Shearn Moody Trust	12,775	12,775
Deferred annuity contracts	6,403,007	7,338,637
Immediate annuity and supplemental contracts	415,726	443,437
Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt securities held to maturity	0	0
Debt securities, available for sale	0	0
Securities available for sale		18,478
Cash and cash equivalents	131,976	217,624
Mortgage loans	0	0
Policy loans	0	0
Other loans	0	0
Derivatives, index options	0	0
Equity securities	17,491	18,478
Life interest in Libbie Shearn Moody Trust	0	0
Deferred annuity contracts	0	0
Immediate annuity and supplemental contracts	0	0
Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt securities held to maturity	7,226,362	7,431,810
Debt securities, available for sale	2,946,059	3,041,131
Securities available for sale		3,041,131
Cash and cash equivalents	0	0
Mortgage loans	0	0
Policy loans	0	0
Other loans	0	0
Derivatives, index options	0	0
Equity securities	0	0
Life interest in Libbie Shearn Moody Trust	0	0
Deferred annuity contracts	0	0
Immediate annuity and supplemental contracts	0	0
Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt securities held to maturity	1,906	2,294
Debt securities, available for sale	0	0
Securities available for sale		0
Cash and cash equivalents	0	0
Mortgage loans	202,762	208,815
Policy loans	90,802	100,230
Other loans	12,709	5,603
Derivatives, index options	14,684	194,731
Equity securities	0	0
Life interest in Libbie Shearn Moody Trust	12,775	12,775
Deferred annuity contracts	6,403,007	7,338,637
Immediate annuity and supplemental contracts	$ 415,726	$ 443,437

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