Segment and Other Operating Information (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Sep. 30, 2014 USD ($)	Jun. 30, 2014 USD ($)	Mar. 31, 2014 USD ($)	Dec. 31, 2015 USD ($) customer	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Selected Condensed Consolidated Balance Sheet Items:
Total segment assets	$ 11,612,576				$ 11,351,892				$ 11,612,576	$ 11,351,892	$ 10,830,416
Other policyholder liabilities	155,261				139,222				155,261	139,222
Condensed Consolidated Income Statements:
Premiums and contract revenues									175,307	170,115	167,466
Net investment income									379,114	505,430	660,432
Other revenues									28,166	21,630	23,716
Realized gains (losses) on investments									7,209	11,605	8,653
Total revenues	180,583	$ 106,104	$ 155,218	$ 147,890	184,315	$ 159,620	$ 206,841	$ 158,003	589,796	708,780	860,267
Life and other policy benefits									67,452	54,295	60,050
Amortization of deferred policy acquisition costs									120,333	115,154	108,233
Universal life and annuity contract interest									176,901	298,259	454,594
Other operating expenses									78,442	83,551	95,693
Federal income taxes (benefit)									45,749	47,873	42,422
Taxes on realized gains (losses) on investments									2,523	4,060	3,028
Taxes on earnings from continuing operations									48,272	51,933	45,450
Segment earnings (loss)									93,710	98,043	90,622
Realized gains (losses) on investments, net of taxes									4,686	7,545	5,625
Net earnings		$ 16,221	$ 28,858	$ 21,326	28,113	$ 28,466	$ 29,183	$ 19,826	98,396	105,588	96,247
Revenues, excluding reinsurance premiums									194,436	189,164	186,207
Reinsurance premiums									(19,129)	(19,049)	(18,741)
United States [Member]
Condensed Consolidated Income Statements:
Revenues, excluding reinsurance premiums									66,750	65,078	64,267
Brazil [Member]
Condensed Consolidated Income Statements:
Revenues, excluding reinsurance premiums									40,640	38,563	38,205
Venezuela [Member]
Condensed Consolidated Income Statements:
Revenues, excluding reinsurance premiums									15,466	14,931	14,017
Taiwan [Member]
Condensed Consolidated Income Statements:
Revenues, excluding reinsurance premiums									14,882	14,166	14,047
Peru
Condensed Consolidated Income Statements:
Revenues, excluding reinsurance premiums									10,915	10,327	9,366
Argentina [Member]
Condensed Consolidated Income Statements:
Revenues, excluding reinsurance premiums									(9,007)	(9,324)	(9,102)
Other foreign countries [Member]
Condensed Consolidated Income Statements:
Revenues, excluding reinsurance premiums									$ 36,776	36,775	37,203
Annuities [Member]
Condensed Consolidated Income Statements:
Number of customers | customer									2
Operating Segments [Member]
Selected Condensed Consolidated Balance Sheet Items:
Deferred policy acquisition costs and sales inducements	1,012,617				962,685				$ 1,012,617	962,685	955,276
Total segment assets	11,452,630				11,187,522				11,452,630	11,187,522	10,657,795
Future policy benefits	9,699,358				9,522,522				9,699,358	9,522,522	9,125,134
Other policyholder liabilities	155,261				139,222				155,261	139,222	142,587
Condensed Consolidated Income Statements:
Premiums and contract revenues									175,307	170,115	167,466
Net investment income									379,114	505,430	660,432
Other revenues									28,166	21,630	23,716
Total revenues									582,587	697,175	851,614
Life and other policy benefits									67,452	54,295	60,050
Amortization of deferred policy acquisition costs									120,333	115,154	108,233
Universal life and annuity contract interest									176,901	298,259	454,594
Other operating expenses									78,442	83,551	95,693
Federal income taxes (benefit)									45,749	47,873	42,422
Total expenses									488,877	599,132	760,992
Segment earnings (loss)									93,710	98,043	90,622
Operating Segments [Member] | Domestic Life Insurance [Member]
Selected Condensed Consolidated Balance Sheet Items:
Deferred policy acquisition costs and sales inducements	78,650				64,279				78,650	64,279	53,540
Total segment assets	868,466				746,051				868,466	746,051	610,570
Future policy benefits	748,853				648,864				748,853	648,864	535,710
Other policyholder liabilities	14,084				12,159				14,084	12,159	11,450
Condensed Consolidated Income Statements:
Premiums and contract revenues									30,743	28,801	29,567
Net investment income									27,172	34,695	33,818
Other revenues									56	55	29
Total revenues									57,971	63,551	63,414
Life and other policy benefits									17,905	11,856	11,660
Amortization of deferred policy acquisition costs									8,647	6,913	6,738
Universal life and annuity contract interest									17,799	27,050	26,427
Other operating expenses									12,774	13,547	15,515
Federal income taxes (benefit)									278	1,373	980
Total expenses									57,403	60,739	61,320
Segment earnings (loss)									568	2,812	2,094
Operating Segments [Member] | International Life Insurance [Member]
Selected Condensed Consolidated Balance Sheet Items:
Deferred policy acquisition costs and sales inducements	251,790				245,353				251,790	245,353	240,468
Total segment assets	1,260,538				1,250,629				1,260,538	1,250,629	1,200,347
Future policy benefits	944,672				953,076				944,672	953,076	913,339
Other policyholder liabilities	16,710				11,898				16,710	11,898	14,618
Condensed Consolidated Income Statements:
Premiums and contract revenues									122,393	118,838	117,668
Net investment income									29,400	51,539	63,504
Other revenues									14	372	299
Total revenues									151,807	170,749	181,471
Life and other policy benefits									24,237	24,034	25,706
Amortization of deferred policy acquisition costs									19,975	21,807	18,946
Universal life and annuity contract interest									23,423	46,255	58,757
Other operating expenses									20,706	23,449	25,624
Federal income taxes (benefit)									20,819	18,112	16,720
Total expenses									109,160	133,657	145,753
Segment earnings (loss)									42,647	37,092	35,718
Operating Segments [Member] | Annuities [Member]
Selected Condensed Consolidated Balance Sheet Items:
Deferred policy acquisition costs and sales inducements	682,177				653,053				682,177	653,053	661,268
Total segment assets	9,054,951				8,933,274				9,054,951	8,933,274	8,586,871
Future policy benefits	8,005,833				7,920,582				8,005,833	7,920,582	7,676,085
Other policyholder liabilities	124,467				115,165				124,467	115,165	116,519
Condensed Consolidated Income Statements:
Premiums and contract revenues									22,171	22,476	20,231
Net investment income									300,198	398,163	543,077
Other revenues									50	68	45
Total revenues									322,419	420,707	563,353
Life and other policy benefits									25,310	18,405	22,684
Amortization of deferred policy acquisition costs									91,711	86,434	82,549
Universal life and annuity contract interest									135,679	224,954	369,410
Other operating expenses									25,723	27,015	33,325
Federal income taxes (benefit)									14,432	20,964	17,660
Total expenses									292,855	377,772	525,628
Segment earnings (loss)									29,564	42,935	37,725
Operating Segments [Member] | All Others [Member]
Selected Condensed Consolidated Balance Sheet Items:
Deferred policy acquisition costs and sales inducements	0				0				0	0	0
Total segment assets	268,675				257,568				268,675	257,568	260,007
Future policy benefits	0				0				0	0	0
Other policyholder liabilities	0				0				0	0	0
Condensed Consolidated Income Statements:
Premiums and contract revenues									0	0	0
Net investment income									22,344	21,033	20,033
Other revenues									28,046	21,135	23,343
Total revenues									50,390	42,168	43,376
Life and other policy benefits									0	0	0
Amortization of deferred policy acquisition costs									0	0	0
Universal life and annuity contract interest									0	0	0
Other operating expenses									19,239	19,540	21,229
Federal income taxes (benefit)									10,220	7,424	7,062
Total expenses									29,459	26,964	28,291
Segment earnings (loss)									20,931	15,204	15,085
Segment Reconciling Items [Member]
Selected Condensed Consolidated Balance Sheet Items:
Total segment assets	$ 159,946				$ 164,370				$ 159,946	$ 164,370	$ 172,621
Agency Two [Member] | Annuities [Member]
Condensed Consolidated Income Statements:
Major customer, percentage of sales									10.00%
Agency One [Member] | Annuities [Member]
Condensed Consolidated Income Statements:
Major customer, percentage of sales									14.00%