Segment and Other Operating Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Selected Condensed Consolidated Balance Sheet Items:
Total segment assets	$ 12,126,318		$ 12,225,094
Other policyholder liabilities	137,109		128,009
Condensed Consolidated Income Statements:
Premiums and contract revenues	42,665	$ 45,585
Net investment income	60,745	171,742
Other revenues	4,997	4,505
Realized gains (losses) on investments	611	2,585
Total revenues	109,018	224,417
Life and other policy benefits	21,401	19,757
Amortization of deferred acquisition costs	32,229	34,212
Universal life and annuity contract interest	(1,818)	109,893
Other operating expenses	23,633	25,092
Total condensed consolidated Federal income taxes	6,698	11,925
Net earnings	26,875	23,538
Segments
Selected Condensed Consolidated Balance Sheet Items:
Deferred policy acquisition costs and sales inducements	979,032		955,081
Total segment assets	11,908,930		12,011,696
Future policy benefits	9,992,199		10,098,484
Other policyholder liabilities	137,109		128,009
Condensed Consolidated Income Statements:
Premiums and contract revenues	42,665	45,585
Net investment income	60,745	171,742
Other revenues	4,997	4,505
Total revenues	108,407	221,832
Life and other policy benefits	21,401	19,757
Amortization of deferred acquisition costs	32,229	34,212
Universal life and annuity contract interest	(1,818)	109,893
Other operating expenses	23,633	25,092
Total condensed consolidated Federal income taxes	6,570	11,020
Total expenses	82,015	199,974
Net earnings	26,392	21,858
Segments | Domestic Life Insurance
Selected Condensed Consolidated Balance Sheet Items:
Deferred policy acquisition costs and sales inducements	106,029		101,253
Total segment assets	1,125,889		1,106,410
Future policy benefits	964,219		950,884
Other policyholder liabilities	14,909		13,643
Condensed Consolidated Income Statements:
Premiums and contract revenues	9,601	8,849
Net investment income	663	19,590
Other revenues	0	13
Total revenues	10,264	28,452
Life and other policy benefits	4,809	4,919
Amortization of deferred acquisition costs	2,675	2,789
Universal life and annuity contract interest	(2,861)	16,247
Other operating expenses	5,147	4,732
Total condensed consolidated Federal income taxes	98	(79)
Total expenses	9,868	28,608
Net earnings	396	(156)
Segments | International Life Insurance
Selected Condensed Consolidated Balance Sheet Items:
Deferred policy acquisition costs and sales inducements	251,225		250,128
Total segment assets	1,231,846		1,236,733
Future policy benefits	906,855		915,384
Other policyholder liabilities	18,380		11,318
Condensed Consolidated Income Statements:
Premiums and contract revenues	27,917	31,500
Net investment income	1,971	18,619
Other revenues	30	26
Total revenues	29,918	50,145
Life and other policy benefits	5,728	6,285
Amortization of deferred acquisition costs	7,380	7,406
Universal life and annuity contract interest	(1,150)	16,382
Other operating expenses	5,381	5,978
Total condensed consolidated Federal income taxes	2,507	4,724
Total expenses	19,846	40,775
Net earnings	10,072	9,370
Segments | Annuities
Selected Condensed Consolidated Balance Sheet Items:
Deferred policy acquisition costs and sales inducements	621,778		603,700
Total segment assets	9,155,547		9,269,956
Future policy benefits	8,121,125		8,232,216
Other policyholder liabilities	103,820		103,048
Condensed Consolidated Income Statements:
Premiums and contract revenues	5,147	5,236
Net investment income	53,543	126,434
Other revenues	19	26
Total revenues	58,709	131,696
Life and other policy benefits	10,864	8,553
Amortization of deferred acquisition costs	22,174	24,017
Universal life and annuity contract interest	2,193	77,264
Other operating expenses	7,935	10,060
Total condensed consolidated Federal income taxes	3,098	3,956
Total expenses	46,264	123,850
Net earnings	12,445	7,846
Segments | All Others
Selected Condensed Consolidated Balance Sheet Items:
Deferred policy acquisition costs and sales inducements	0		0
Total segment assets	395,648		398,597
Future policy benefits	0		0
Other policyholder liabilities	0		0
Condensed Consolidated Income Statements:
Premiums and contract revenues	0	0
Net investment income	4,568	7,099
Other revenues	4,948	4,440
Total revenues	9,516	11,539
Life and other policy benefits	0	0
Amortization of deferred acquisition costs	0	0
Universal life and annuity contract interest	0	0
Other operating expenses	5,170	4,322
Total condensed consolidated Federal income taxes	867	2,419
Total expenses	6,037	6,741
Net earnings	3,479	4,798
Other unallocated
Selected Condensed Consolidated Balance Sheet Items:
Total segment assets	217,388		$ 213,398
Segment Reconciling Items
Condensed Consolidated Income Statements:
Taxes on realized gains (losses) on investments	128	905
Realized gains (losses) on investments, net of taxes	$ 483	$ 1,680