Segment and Other Operating Information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Selected Condensed Consolidated Balance Sheet Items:
Total segment assets	$ 11,351,892				$ 10,830,416				$ 11,351,892	$ 10,830,416	$ 10,263,858
Other policyholder liabilities	139,222				142,587				139,222	142,587
Condensed Consolidated Income Statements:
Premiums and contract revenues									170,115	167,466	167,944
Net investment income									505,430	660,432	460,048
Other revenues									21,630	23,716	23,470
Realized gains (losses) on investments									11,605	8,653	13,200
Total revenues	184,315	159,620	206,841	158,003	258,184	188,192	182,859	231,032	708,780	860,267	664,662
Life and other policy benefits									54,295	60,050	51,842
Amortization of deferred policy acquisition costs									115,154	108,233	121,922
Universal life and annuity contract interest									298,259	454,594	262,339
Other operating expenses									83,551	95,693	87,978
Federal income taxes (benefit)									47,873	42,422	43,403
Taxes on realized gains (losses) on investments									4,060	3,028	4,620
Income Tax Expense (Benefit)									51,933	45,450	48,023
Segment earnings (loss)									98,043	90,622	83,978
Realized gains (losses) on investments, net of taxes									7,545	5,625	8,580
Net Earnings	28,113	28,466	29,183	19,826	27,842	24,782	26,991	16,632	105,588	96,247	92,558
Revenues, excluding reinsurance premiums									189,164	186,207	187,728
Reinsurance premiums									(19,049)	(18,741)	(19,784)
United States [Member]
Condensed Consolidated Income Statements:
Revenues, excluding reinsurance premiums									65,078	64,267	67,924
Brazil [Member]
Condensed Consolidated Income Statements:
Revenues, excluding reinsurance premiums									38,563	38,205	38,605
Taiwan [Member]
Condensed Consolidated Income Statements:
Revenues, excluding reinsurance premiums									14,166	14,047	13,958
Argentina [Member]
Condensed Consolidated Income Statements:
Revenues, excluding reinsurance premiums									(9,324)	(9,102)	(9,818)
Venezuela [Member]
Condensed Consolidated Income Statements:
Revenues, excluding reinsurance premiums									14,931	14,017	12,223
Peru
Condensed Consolidated Income Statements:
Revenues, excluding reinsurance premiums									10,327	9,366	8,691
Other foreign countries [Member]
Condensed Consolidated Income Statements:
Revenues, excluding reinsurance premiums									36,775	37,203	36,509
Annuities [Member]
Condensed Consolidated Income Statements:
Major customer, percentage of sales									16.00%
Operating Segments [Member]
Selected Condensed Consolidated Balance Sheet Items:
Deferred policy acquisition costs and sales inducements	962,685				955,276				962,685	955,276	858,241
Total segment assets	11,187,522				10,657,795				11,187,522	10,657,795	10,081,280
Future policy benefits	9,522,523				9,125,134				9,522,523	9,125,134	8,568,854
Other policyholder liabilities	139,222				142,587				139,222	142,587	148,561
Condensed Consolidated Income Statements:
Premiums and contract revenues									170,115	167,466	167,944
Net investment income									505,430	660,432	460,048
Other revenues									21,630	23,716	23,470
Total revenues									697,175	851,614	651,462
Life and other policy benefits									54,295	60,050	51,842
Amortization of deferred policy acquisition costs									115,154	108,233	121,922
Universal life and annuity contract interest									298,259	454,594	262,339
Other operating expenses									83,551	95,693	87,978
Federal income taxes (benefit)									47,873	42,422	43,403
Total expenses									599,132	760,992	567,484
Segment earnings (loss)									98,043	90,622	83,978
Operating Segments [Member] | Domestic Life Insurance [Member]
Selected Condensed Consolidated Balance Sheet Items:
Deferred policy acquisition costs and sales inducements	64,279				53,540				64,279	53,540	40,810
Total segment assets	746,051				610,570				746,051	610,570	463,569
Future policy benefits	648,865				535,710				648,865	535,710	398,202
Other policyholder liabilities	12,159				11,450				12,159	11,450	10,468
Condensed Consolidated Income Statements:
Premiums and contract revenues									28,801	29,567	31,143
Net investment income									34,695	33,818	21,194
Other revenues									55	29	62
Total revenues									63,551	63,414	52,399
Life and other policy benefits									11,856	11,660	10,633
Amortization of deferred policy acquisition costs									6,913	6,738	7,461
Universal life and annuity contract interest									27,050	26,427	17,507
Other operating expenses									13,547	15,515	14,895
Federal income taxes (benefit)									1,373	980	648
Total expenses									60,739	61,320	51,144
Segment earnings (loss)									2,812	2,094	1,255
Operating Segments [Member] | International Life Insurance [Member]
Selected Condensed Consolidated Balance Sheet Items:
Deferred policy acquisition costs and sales inducements	245,353				240,468				245,353	240,468	226,899
Total segment assets	1,250,629				1,200,347				1,250,629	1,200,347	1,105,862
Future policy benefits	953,076				913,339				953,076	913,339	846,028
Other policyholder liabilities	11,898				14,618				11,898	14,618	13,074
Condensed Consolidated Income Statements:
Premiums and contract revenues									118,838	117,668	114,605
Net investment income									51,539	63,504	43,469
Other revenues									372	299	485
Total revenues									170,749	181,471	158,559
Life and other policy benefits									24,034	25,706	20,877
Amortization of deferred policy acquisition costs									21,807	18,946	18,103
Universal life and annuity contract interest									46,255	58,757	39,639
Other operating expenses									23,449	25,624	26,007
Federal income taxes (benefit)									18,112	16,720	18,377
Total expenses									133,657	145,753	123,003
Segment earnings (loss)									37,092	35,718	35,556
Operating Segments [Member] | Annuities [Member]
Selected Condensed Consolidated Balance Sheet Items:
Deferred policy acquisition costs and sales inducements	653,053				661,268				653,053	661,268	590,532
Total segment assets	8,933,274				8,586,871				8,933,274	8,586,871	8,269,445
Future policy benefits	7,920,582				7,676,085				7,920,582	7,676,085	7,324,624
Other policyholder liabilities	115,165				116,519				115,165	116,519	125,019
Condensed Consolidated Income Statements:
Premiums and contract revenues									22,476	20,231	22,196
Net investment income									398,163	543,077	375,431
Other revenues									68	45	80
Total revenues									420,707	563,353	397,707
Life and other policy benefits									18,405	22,684	20,332
Amortization of deferred policy acquisition costs									86,434	82,549	96,358
Universal life and annuity contract interest									224,954	369,410	205,193
Other operating expenses									27,015	33,325	25,456
Federal income taxes (benefit)									20,964	17,660	17,162
Total expenses									377,772	525,628	364,501
Segment earnings (loss)									42,935	37,725	33,206
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	257,568				260,007				257,568	260,007	242,404
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									21,033	20,033	19,954
Other revenues									21,135	23,343	22,843
Total revenues									42,168	43,376	42,797
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									19,540	21,229	21,620
Federal income taxes (benefit)									7,424	7,062	7,216
Total expenses									26,964	28,291	28,836
Segment earnings (loss)									15,204	15,085	13,961
Segment Reconciling Items [Member]
Selected Condensed Consolidated Balance Sheet Items:
Total segment assets	$ 164,370				$ 172,621				$ 164,370	$ 172,621	$ 182,578