Business Segments - Reconciliation of Segment Operating Information to Consolidated Statement of Operations (Details) - USD ($) $ in Thousands	3 Months Ended				9 Months Ended
	Sep. 30, 2016		Sep. 30, 2015		Sep. 30, 2016		Sep. 30, 2015
Revenue:
Premium	$ 783,411	[1]	$ 748,109	[2]	$ 2,349,126	[1]	$ 2,242,649	[2]
Net investment income	202,720	[1]	193,213	[2]	601,415	[1]	579,632	[2]
Other income	160	[1]	692	[2]	963	[1]	2,052	[2]
Total revenue	986,291		942,014		2,951,504		2,824,333
Expenses:
Policy benefits	532,152	[1]	501,156	[2]	1,588,610	[1]	1,507,247	[2]
Required interest on reserves	0		0		0		0
Required interest on DAC	0		0		0		0
Amortization of acquisition costs	116,821	[1]	111,643	[2]	352,872	[1]	334,041	[2]
Commissions, premium taxes, and non-deferred acquisition costs	61,153	[1]	59,918	[2]	185,609	[1]	176,155	[2]
Insurance administrative expense	49,505		47,169		146,386		138,594
Parent expense	1,955		2,177		6,360		6,662
Stock compensation expense	6,345		6,836		20,334		21,877
Interest expense	20,381	[1]	19,246	[2]	62,860	[1]	57,420	[2]
Total benefits and expenses	788,312	[1]	748,145	[2]	2,363,031	[1]	2,241,996	[2]
Subtotal	197,979		193,869		588,473		582,337
Non-operating items	(257)		0		(257)		0
Measure of segment profitability (pretax)	198,236		193,869		588,730		582,337
Deduct applicable income taxes	(58,422)		(63,352)		(178,842)		(190,291)
Segment profits after tax	139,814		130,517		409,888		392,046
Add (deduct) realized investment gains (losses)	3,482		5,140		7,780		7,872
Pretax income from continuing operations per Condensed Consolidated Statements of Operations	201,461	[1]	199,009	[2]	596,253	[1]	590,209	[2]
Operating Segments [Member] | Life [Member]
Revenue:
Premium	546,415		518,929		1,639,156		1,552,309
Total revenue	546,415		518,929		1,639,156		1,552,309
Expenses:
Policy benefits	369,546		342,196		1,101,748		1,029,261
Required interest on reserves	(145,295)		(138,649)		(430,931)		(412,264)
Required interest on DAC	44,950		43,354		133,628		129,339
Amortization of acquisition costs	93,496		88,376		281,698		265,641
Commissions, premium taxes, and non-deferred acquisition costs	40,577		39,552		121,968		115,452
Total benefits and expenses	403,274		374,829		1,208,111		1,127,429
Subtotal	143,141		144,100		431,045		424,880
Measure of segment profitability (pretax)	143,141		144,100		431,045		424,880
Operating Segments [Member] | Health [Member]
Revenue:
Premium	236,987		229,139		709,936		690,221
Total revenue	236,987		229,139		709,936		690,221
Expenses:
Policy benefits	153,351		149,312		459,387		448,539
Required interest on reserves	(18,476)		(17,416)		(54,803)		(51,450)
Required interest on DAC	5,789		5,700		17,297		17,058
Amortization of acquisition costs	22,643		20,934		67,110		61,858
Commissions, premium taxes, and non-deferred acquisition costs	20,604		20,402		63,733		60,820
Total benefits and expenses	183,911		178,932		552,724		536,825
Subtotal	53,076		50,207		157,212		153,396
Measure of segment profitability (pretax)	53,076		50,207		157,212		153,396
Operating Segments [Member] | Annuity [Member]
Revenue:
Premium	9		41		34		119
Total revenue	9		41		34		119
Expenses:
Policy benefits	9,255		9,648		27,475		29,447
Required interest on reserves	(12,761)		(13,328)		(38,359)		(40,084)
Required interest on DAC	192		278		621		885
Amortization of acquisition costs	682		2,333		4,064		6,542
Commissions, premium taxes, and non-deferred acquisition costs	11		9		31		32
Total benefits and expenses	(2,621)		(1,060)		(6,168)		(3,178)
Subtotal	2,630		1,101		6,202		3,297
Measure of segment profitability (pretax)	2,630		1,101		6,202		3,297
Operating Segments [Member] | Investment [Member]
Revenue:
Net investment income	202,720		193,213		601,415		579,632
Total revenue	202,720		193,213		601,415		579,632
Expenses:
Required interest on reserves	176,532		169,393		524,093		503,798
Required interest on DAC	(50,931)		(49,332)		(151,546)		(147,282)
Interest expense	20,381		19,246		62,860		57,420
Total benefits and expenses	145,982		139,307		435,407		413,936
Subtotal	56,738		53,906		166,008		165,696
Measure of segment profitability (pretax)	56,738		53,906		166,008		165,696
Operating Segments [Member] | Other & Corporate [Member]
Revenue:
Other income	199		737		1,086		2,201
Total revenue	199		737		1,086		2,201
Expenses:
Insurance administrative expense	49,248		47,169		146,129		138,594
Parent expense	1,955		2,177		6,360		6,662
Stock compensation expense	6,345		6,836		20,334		21,877
Total benefits and expenses	57,548		56,182		172,823		167,133
Subtotal	(57,349)		(55,445)		(171,737)		(164,932)
Measure of segment profitability (pretax)	(57,349)		(55,445)		(171,737)		(164,932)
Adjustments [Member]
Revenue:
Other income	(39)		(45)		(123)		(149)
Total revenue	(39)		(45)		(123)		(149)
Expenses:
Commissions, premium taxes, and non-deferred acquisition costs	(39)		(45)		(123)		(149)
Insurance administrative expense	257				257
Total benefits and expenses	218		(45)		134		(149)
Subtotal	(257)		0		(257)		0
Non-operating items	(257)		0		(257)		0
Measure of segment profitability (pretax)	$ 0		$ 0		$ 0		$ 0

[1] Due to the adoption of ASU 2016-09, certain balances related to excess tax benefits from stock compensation were adjusted prospectively as described in Note 2—New Accounting Standards.

[2] Certain prior year balances were adjusted to give effect to discontinued operations as described in Note 5—Discontinued Operations.