Segment and Other Operating Information (Details)
$ in Thousands
 3 Months Ended 12 Months Ended
Dec. 31, 2016
USD ($)
Sep. 30, 2016
USD ($)
Jun. 30, 2016
USD ($)
Mar. 31, 2016
USD ($)
Dec. 31, 2015
USD ($)
Sep. 30, 2015
USD ($)
Jun. 30, 2015
USD ($)
Mar. 31, 2015
USD ($)
Dec. 31, 2016
USD ($)
customer
Dec. 31, 2015
USD ($)
Dec. 31, 2014
USD ($)
Selected Condensed Consolidated Balance Sheet Items:                      
Total segment assets $ 11,894,981       $ 11,612,576       $ 11,894,981 $ 11,612,576 $ 11,351,892
Other policyholder liabilities 143,391       155,261       143,391 155,261  
Condensed Consolidated Income Statements:                      
Premiums and contract revenues                 182,723 175,307 170,115
Net investment income                 467,674 379,114 505,430
Other revenues                 18,901 28,166 21,630
Realized gains (losses) on investments                 13,070 7,209 11,605
Total revenues 184,485 $ 181,847 $ 167,094 $ 148,942 180,583 $ 106,104 $ 155,218 $ 147,890 682,368 589,796 708,780
Life and other policy benefits                 65,529 67,452 54,295
Amortization of deferred policy acquisition costs                 121,139 120,333 115,154
Universal life and annuity contract interest                 248,390 176,901 298,259
Other operating expenses                 94,448 78,442 83,551
Federal income taxes (benefit)                 47,395 45,749 47,873
Taxes on realized gains (losses) on investments                 4,575 2,523 4,060
Taxes on earnings from continuing operations                 51,970 48,272 51,933
Segment earnings (loss)                 92,397 93,710 98,043
Realized gains (losses) on investments, net of taxes                 8,495 4,686 7,545
Net earnings 23,612 $ 33,736 $ 26,286 $ 17,259 31,991 $ 16,221 $ 28,858 $ 21,326 100,892 98,396 105,588
Revenues, excluding reinsurance premiums                 202,398 194,436 189,164
Reinsurance premiums                 (19,675) (19,129) (19,049)
United States                      
Condensed Consolidated Income Statements:                      
Revenues, excluding reinsurance premiums                 75,405 66,750 65,078
Brazil                      
Condensed Consolidated Income Statements:                      
Revenues, excluding reinsurance premiums                 38,928 40,640 38,563
Venezuela                      
Condensed Consolidated Income Statements:                      
Revenues, excluding reinsurance premiums                 15,534 15,466 14,931
Taiwan                      
Condensed Consolidated Income Statements:                      
Revenues, excluding reinsurance premiums                 14,474 14,882 14,166
Peru                      
Condensed Consolidated Income Statements:                      
Revenues, excluding reinsurance premiums                 11,378 10,915 10,327
Argentina                      
Condensed Consolidated Income Statements:                      
Revenues, excluding reinsurance premiums                 9,548 9,007 9,324
Other foreign countries                      
Condensed Consolidated Income Statements:                      
Revenues, excluding reinsurance premiums                 $ 37,131 36,776 36,775
Annuities                      
Condensed Consolidated Income Statements:                      
Number of customers | customer                 2    
Operating Segments                      
Selected Condensed Consolidated Balance Sheet Items:                      
Deferred policy acquisition costs and sales inducements 982,305       1,012,617       $ 982,305 1,012,617 962,685
Total segment assets 11,697,099       11,452,630       11,697,099 11,452,630 11,187,522
Future policy benefits 9,859,095       9,699,358       9,859,095 9,699,358 9,522,522
Other policyholder liabilities 143,391       155,261       143,391 155,261 139,222
Condensed Consolidated Income Statements:                      
Premiums and contract revenues                 182,723 175,307 170,115
Net investment income                 467,674 379,114 505,430
Other revenues                 18,901 28,166 21,630
Total revenues                 669,298 582,587 697,175
Life and other policy benefits                 65,529 67,452 54,295
Amortization of deferred policy acquisition costs                 121,139 120,333 115,154
Universal life and annuity contract interest                 248,390 176,901 298,259
Other operating expenses                 94,448 78,442 83,551
Federal income taxes (benefit)                 47,395 45,749 47,873
Total expenses                 576,901 488,877 599,132
Segment earnings (loss)                 92,397 93,710 98,043
Operating Segments | Domestic Life Insurance                      
Selected Condensed Consolidated Balance Sheet Items:                      
Deferred policy acquisition costs and sales inducements 90,485       78,650       90,485 78,650 64,279
Total segment assets 971,990       868,466       971,990 868,466 746,051
Future policy benefits 830,460       748,853       830,460 748,853 648,864
Other policyholder liabilities 13,998       14,084       13,998 14,084 12,159
Condensed Consolidated Income Statements:                      
Premiums and contract revenues                 34,728 30,743 28,801
Net investment income                 39,691 27,172 34,695
Other revenues                 119 56 55
Total revenues                 74,538 57,971 63,551
Life and other policy benefits                 17,908 17,905 11,856
Amortization of deferred policy acquisition costs                 4,125 8,647 6,913
Universal life and annuity contract interest                 28,606 17,799 27,050
Other operating expenses                 18,739 12,774 13,547
Federal income taxes (benefit)                 1,749 278 1,373
Total expenses                 71,127 57,403 60,739
Segment earnings (loss)                 3,411 568 2,812
Operating Segments | International Life Insurance                      
Selected Condensed Consolidated Balance Sheet Items:                      
Deferred policy acquisition costs and sales inducements 243,106       251,790       243,106 251,790 245,353
Total segment assets 1,232,648       1,260,538       1,232,648 1,260,538 1,250,629
Future policy benefits 919,380       944,672       919,380 944,672 953,076
Other policyholder liabilities 10,528       16,710       10,528 16,710 11,898
Condensed Consolidated Income Statements:                      
Premiums and contract revenues                 125,775 122,393 118,838
Net investment income                 42,331 29,400 51,539
Other revenues                 321 14 372
Total revenues                 168,427 151,807 170,749
Life and other policy benefits                 18,759 24,237 24,034
Amortization of deferred policy acquisition costs                 18,027 19,975 21,807
Universal life and annuity contract interest                 28,636 23,423 46,255
Other operating expenses                 25,933 20,706 23,449
Federal income taxes (benefit)                 26,130 20,819 18,112
Total expenses                 117,485 109,160 133,657
Segment earnings (loss)                 50,942 42,647 37,092
Operating Segments | Annuities                      
Selected Condensed Consolidated Balance Sheet Items:                      
Deferred policy acquisition costs and sales inducements 648,714       682,177       648,714 682,177 653,053
Total segment assets 9,193,980       9,054,951       9,193,980 9,054,951 8,933,274
Future policy benefits 8,109,255       8,005,833       8,109,255 8,005,833 7,920,582
Other policyholder liabilities 118,865       124,467       118,865 124,467 115,165
Condensed Consolidated Income Statements:                      
Premiums and contract revenues                 22,220 22,171 22,476
Net investment income                 362,700 300,198 398,163
Other revenues                 254 50 68
Total revenues                 385,174 322,419 420,707
Life and other policy benefits                 28,862 25,310 18,405
Amortization of deferred policy acquisition costs                 98,987 91,711 86,434
Universal life and annuity contract interest                 191,148 135,679 224,954
Other operating expenses                 31,852 25,723 27,015
Federal income taxes (benefit)                 11,638 14,432 20,964
Total expenses                 362,487 292,855 377,772
Segment earnings (loss)                 22,687 29,564 42,935
Operating Segments | All Others                      
Selected Condensed Consolidated Balance Sheet Items:                      
Deferred policy acquisition costs and sales inducements 0       0       0 0 0
Total segment assets 298,481       268,675       298,481 268,675 257,568
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                 22,952 22,344 21,033
Other revenues                 18,207 28,046 21,135
Total revenues                 41,159 50,390 42,168
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                 17,924 19,239 19,540
Federal income taxes (benefit)                 7,878 10,220 7,424
Total expenses                 25,802 29,459 26,964
Segment earnings (loss)                 15,357 20,931 15,204
Segment Reconciling Items                      
Selected Condensed Consolidated Balance Sheet Items:                      
Total segment assets $ 197,882       $ 159,946       $ 197,882 $ 159,946 $ 164,370
Agency Two | Annuities                      
Condensed Consolidated Income Statements:                      
Major customer, percentage of sales                 12.00%    
Agency One | Annuities                      
Condensed Consolidated Income Statements:                      
Major customer, percentage of sales                 11.00%