Segment and Other Operating Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Selected Condensed Consolidated Balance Sheet Items:
Total segment assets	$ 12,559,594		$ 12,559,594		$ 11,931,691
Other policyholder liabilities	129,715		129,715		135,694
Condensed Consolidated Income Statements:
Premiums and contract revenues	61,939	$ 42,496	178,195	$ 130,035
Net investment income	108,456	175,553	388,211	358,100
Other revenues	3,273	5,111	13,652	15,396
Total revenues	173,166	225,435	583,760	509,113
Life and other policy benefits	39,918	5,744	101,764	44,607
Amortization of deferred policy acquisition costs and value of business acquired	22,998	26,775	86,573	90,073
Universal life and annuity contract interest	59,445	124,145	200,500	183,316
Other operating expenses	25,813	24,037	77,196	72,467
Total condensed consolidated Federal income taxes	5,003	9,093	23,844	23,668
Net earnings	19,989	35,641	93,883	94,982
Realized gains (losses) on investments	(502)	2,275	3,702	5,582
Segments
Selected Condensed Consolidated Balance Sheet Items:
Deferred policy acquisition costs, sales inducements, and value of business acquired	985,151		985,151		975,418
Total segment assets	12,166,550		12,166,550		11,588,481
Future policy benefits	10,162,726		10,162,726		9,744,286
Other policyholder liabilities	129,715		129,715		135,694
Condensed Consolidated Income Statements:
Premiums and contract revenues	61,939	42,496	178,195	130,035
Net investment income	108,456	175,553	388,211	358,100
Other revenues	3,273	5,111	13,652	15,396
Total revenues	173,668	223,160	580,058	503,531
Life and other policy benefits	39,918	5,744	101,764	44,607
Amortization of deferred policy acquisition costs and value of business acquired	22,998	26,775	86,573	90,073
Universal life and annuity contract interest	59,445	124,145	200,500	183,316
Other operating expenses	25,813	24,037	77,196	72,467
Total condensed consolidated Federal income taxes	5,109	8,615	23,067	22,496
Total expenses	153,283	189,316	489,100	412,959
Net earnings	20,385	33,844	90,958	90,572
Segments | Domestic Life Insurance
Selected Condensed Consolidated Balance Sheet Items:
Deferred policy acquisition costs, sales inducements, and value of business acquired	123,348		123,348		122,661
Total segment assets	1,330,245		1,330,245		1,215,864
Future policy benefits	1,144,243		1,144,243		1,039,150
Other policyholder liabilities	16,811		16,811		17,439
Condensed Consolidated Income Statements:
Premiums and contract revenues	11,387	10,060	32,897	29,775
Net investment income	12,885	26,912	51,379	41,131
Other revenues	49	11	113	12
Total revenues	24,321	36,983	84,389	70,918
Life and other policy benefits	6,099	5,839	13,850	15,751
Amortization of deferred policy acquisition costs and value of business acquired	2,181	2,978	8,898	8,362
Universal life and annuity contract interest	11,267	22,355	45,693	29,401
Other operating expenses	5,297	5,215	14,437	15,368
Total condensed consolidated Federal income taxes	(107)	122	306	405
Total expenses	24,737	36,509	83,184	69,287
Net earnings	(416)	474	1,205	1,631
Segments | International Life Insurance
Selected Condensed Consolidated Balance Sheet Items:
Deferred policy acquisition costs, sales inducements, and value of business acquired	217,307		217,307		243,518
Total segment assets	1,166,237		1,166,237		1,211,036
Future policy benefits	874,980		874,980		894,891
Other policyholder liabilities	13,512		13,512		20,381
Condensed Consolidated Income Statements:
Premiums and contract revenues	25,065	26,839	74,905	82,218
Net investment income	6,872	19,731	30,165	32,305
Other revenues	25	5	79	39
Total revenues	31,962	46,575	105,149	114,562
Life and other policy benefits	5,074	6,609	10,195	16,872
Amortization of deferred policy acquisition costs and value of business acquired	(3,047)	6,307	11,195	21,023
Universal life and annuity contract interest	14,637	30,596	33,967	37,046
Other operating expenses	5,493	4,982	14,278	15,991
Total condensed consolidated Federal income taxes	1,970	(322)	7,192	4,701
Total expenses	24,127	48,172	76,827	95,633
Net earnings	7,835	(1,597)	28,322	18,929
Segments | Annuities
Selected Condensed Consolidated Balance Sheet Items:
Deferred policy acquisition costs, sales inducements, and value of business acquired	501,745		501,745		609,239
Total segment assets	8,324,924		8,324,924		8,791,463
Future policy benefits	7,442,615		7,442,615		7,810,245
Other policyholder liabilities	85,290		85,290		97,874
Condensed Consolidated Income Statements:
Premiums and contract revenues	5,336	5,597	16,061	18,042
Net investment income	78,000	123,525	270,727	263,983
Other revenues	8	11	80	48
Total revenues	83,344	129,133	286,868	282,073
Life and other policy benefits	12,550	(6,704)	33,856	11,984
Amortization of deferred policy acquisition costs and value of business acquired	21,688	17,490	60,150	60,688
Universal life and annuity contract interest	33,541	71,194	120,840	116,869
Other operating expenses	8,596	8,719	25,478	25,741
Total condensed consolidated Federal income taxes	1,388	7,714	9,426	13,290
Total expenses	77,763	98,413	249,750	228,572
Net earnings	5,581	30,720	37,118	53,501
Segments | Acquired Businesses
Selected Condensed Consolidated Balance Sheet Items:
Deferred policy acquisition costs, sales inducements, and value of business acquired	142,751		142,751		0
Total segment assets	970,890		970,890		0
Future policy benefits	700,888		700,888		0
Other policyholder liabilities	14,102		14,102		0
Condensed Consolidated Income Statements:
Premiums and contract revenues	20,151	0	54,332	0
Net investment income	6,300	0	16,283	0
Other revenues	2,318	0	6,049	0
Total revenues	28,769	0	76,664	0
Life and other policy benefits	16,195	0	43,863	0
Amortization of deferred policy acquisition costs and value of business acquired	2,176	0	6,330	0
Universal life and annuity contract interest	0	0	0	0
Other operating expenses	4,772	0	12,348	0
Total condensed consolidated Federal income taxes	1,133	0	2,836	0
Total expenses	24,276	0	65,377	0
Net earnings	4,493	0	11,287	0
Segments | All Others
Selected Condensed Consolidated Balance Sheet Items:
Deferred policy acquisition costs, sales inducements, and value of business acquired	0		0		0
Total segment assets	374,254		374,254		370,118
Future policy benefits	0		0		0
Other policyholder liabilities	0		0		0
Condensed Consolidated Income Statements:
Premiums and contract revenues	0	0	0	0
Net investment income	4,399	5,385	19,657	20,681
Other revenues	873	5,084	7,331	15,297
Total revenues	5,272	10,469	26,988	35,978
Life and other policy benefits	0	0	0	0
Amortization of deferred policy acquisition costs and value of business acquired	0	0	0	0
Universal life and annuity contract interest	0	0	0	0
Other operating expenses	1,655	5,121	10,655	15,367
Total condensed consolidated Federal income taxes	725	1,101	3,307	4,100
Total expenses	2,380	6,222	13,962	19,467
Net earnings	2,892	4,247	13,026	16,511
Other unallocated
Selected Condensed Consolidated Balance Sheet Items:
Total segment assets	393,044		393,044		$ 343,210
Segment Reconciling Items
Condensed Consolidated Income Statements:
Taxes on realized gains (losses) on investments	(106)	478	777	1,172
Realized gains (losses) on investments, net of taxes	$ (396)	$ 1,797	$ 2,925	$ 4,410