Business Segments - Reconciliation of Segment Operating Information to Consolidated Statement of Operations (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Revenue:
Premium	$ 820,631	$ 779,860
Net investment income	208,282	197,053
Other income	416	421
Total revenue	1,029,329	977,334
Expenses:
Policy benefits	557,776	524,973
Required interest on reserves	0	0
Required interest on DAC	0	0
Amortization of acquisition costs	125,908	118,806
Commissions, premium taxes, and non-deferred acquisition costs	65,116	61,602
Insurance administrative expense	51,913	48,468
Parent expense	2,233	2,026
Stock compensation expense	8,195	6,935
Interest expense	20,699	19,369
Total benefits and expenses	831,840	782,179
Subtotal	197,489	195,155
Non-operating items	0	0
Measure of segment profitability (pretax)	197,489	195,155
Deduct applicable income taxes	(58,818)	(61,771)
Segment profits after tax	138,671	133,384
Add (deduct) realized investment gains (losses)	(5,748)	293
Pretax income from continuing operations per Condensed Consolidated Statements of Operations	191,741	195,448
Operating Segments [Member] | Life [Member]
Revenue:
Premium	575,837	544,151
Total revenue	575,837	544,151
Expenses:
Policy benefits	391,079	362,860
Required interest on reserves	(148,825)	(142,011)
Required interest on DAC	45,936	44,202
Amortization of acquisition costs	99,905	94,539
Commissions, premium taxes, and non-deferred acquisition costs	43,638	40,261
Total benefits and expenses	431,733	399,851
Subtotal	144,104	144,300
Measure of segment profitability (pretax)	144,104	144,300
Operating Segments [Member] | Health [Member]
Revenue:
Premium	244,791	235,697
Total revenue	244,791	235,697
Expenses:
Policy benefits	157,751	152,775
Required interest on reserves	(18,975)	(18,076)
Required interest on DAC	5,809	5,742
Amortization of acquisition costs	25,327	22,365
Commissions, premium taxes, and non-deferred acquisition costs	21,502	21,376
Total benefits and expenses	191,414	184,182
Subtotal	53,377	51,515
Measure of segment profitability (pretax)	53,377	51,515
Operating Segments [Member] | Annuity [Member]
Revenue:
Premium	3	12
Total revenue	3	12
Expenses:
Policy benefits	8,946	9,338
Required interest on reserves	(12,418)	(13,092)
Required interest on DAC	178	224
Amortization of acquisition costs	676	1,902
Commissions, premium taxes, and non-deferred acquisition costs	11	9
Total benefits and expenses	(2,607)	(1,619)
Subtotal	2,610	1,631
Measure of segment profitability (pretax)	2,610	1,631
Operating Segments [Member] | Investment [Member]
Revenue:
Net investment income	208,282	197,053
Total revenue	208,282	197,053
Expenses:
Required interest on reserves	180,218	173,179
Required interest on DAC	(51,923)	(50,168)
Interest expense	20,699	19,369
Total benefits and expenses	148,994	142,380
Subtotal	59,288	54,673
Measure of segment profitability (pretax)	59,288	54,673
Operating Segments [Member] | Other & Corporate [Member]
Revenue:
Other income	451	465
Total revenue	451	465
Expenses:
Insurance administrative expense	51,913	48,468
Parent expense	2,233	2,026
Stock compensation expense	8,195	6,935
Total benefits and expenses	62,341	57,429
Subtotal	(61,890)	(56,964)
Measure of segment profitability (pretax)	(61,890)	(56,964)
Adjustments [Member]
Revenue:
Other income	(35)	(44)
Total revenue	(35)	(44)
Expenses:
Commissions, premium taxes, and non-deferred acquisition costs	(35)	(44)
Insurance administrative expense
Total benefits and expenses	(35)	(44)
Subtotal	0	0
Non-operating items	0	0
Measure of segment profitability (pretax)	$ 0	$ 0