Business Segments - Reconciliation of Segment Operating Information to Consolidated Statement of Operations (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016		Mar. 31, 2015
Revenue:
Premium	$ 779,860	[1]	$ 742,056	[2]
Net investment income	197,053	[1]	191,596	[2]
Other income	421	[1]	669	[2]
Total revenue	977,334		934,321
Expenses:
Policy benefits	524,973	[1]	497,775	[2]
Required interest on reserves	0		0
Required interest on DAC	0		0
Amortization of acquisition costs	118,806	[1]	110,660	[2]
Commissions, premium taxes, and non-deferred acquisition costs	61,602	[1]	57,105	[2]
Insurance administrative expense	48,468		45,951
Parent expense	2,026		2,173
Stock compensation expense	6,935		7,239
Interest expense	19,369	[1]	19,060	[2]
Total benefits and expenses	782,179	[1]	739,963	[2]
Subtotal	195,155		194,358
Nonoperating items	0		0
Measure of segment profitability (pretax)	195,155		194,358
Deduct applicable income taxes	(61,771)		(63,657)
Segment profits after tax	133,384		130,701
Add (deduct) realized investment gains (losses)	293		119
Income before income taxes	195,448	[1]	194,477	[2]
Operating Segments [Member] | Life [Member]
Revenue:
Premium	544,151		513,342
Total revenue	544,151		513,342
Expenses:
Policy benefits	362,860		339,701
Required interest on reserves	(142,011)		(136,185)
Required interest on DAC	44,202		42,846
Amortization of acquisition costs	94,539		88,528
Commissions, premium taxes, and non-deferred acquisition costs	40,261		37,049
Total benefits and expenses	399,851		371,939
Subtotal	144,300		141,403
Measure of segment profitability (pretax)	144,300		141,403
Operating Segments [Member] | Health [Member]
Revenue:
Premium	235,697		228,673
Total revenue	235,697		228,673
Expenses:
Policy benefits	152,775		148,029
Required interest on reserves	(18,076)		(16,883)
Required interest on DAC	5,742		5,668
Amortization of acquisition costs	22,365		20,184
Commissions, premium taxes, and non-deferred acquisition costs	21,376		20,098
Total benefits and expenses	184,182		177,096
Subtotal	51,515		51,577
Measure of segment profitability (pretax)	51,515		51,577
Operating Segments [Member] | Annuity [Member]
Revenue:
Premium	12		41
Total revenue	12		41
Expenses:
Policy benefits	9,338		10,045
Required interest on reserves	(13,092)		(13,369)
Required interest on DAC	224		313
Amortization of acquisition costs	1,902		1,948
Commissions, premium taxes, and non-deferred acquisition costs	9		11
Total benefits and expenses	(1,619)		(1,052)
Subtotal	1,631		1,093
Measure of segment profitability (pretax)	1,631		1,093
Operating Segments [Member] | Investment [Member]
Revenue:
Net investment income	197,053		191,596
Total revenue	197,053		191,596
Expenses:
Required interest on reserves	173,179		166,437
Required interest on DAC	(50,168)		(48,827)
Interest expense	19,369		19,060
Total benefits and expenses	142,380		136,670
Subtotal	54,673		54,926
Measure of segment profitability (pretax)	54,673		54,926
Operating Segments [Member] | Other & Corporate [Member]
Revenue:
Other income	465		722
Total revenue	465		722
Expenses:
Insurance administrative expense	48,468		45,951
Parent expense	2,026		2,173
Stock compensation expense	6,935		7,239
Total benefits and expenses	57,429		55,363
Subtotal	(56,964)		(54,641)
Measure of segment profitability (pretax)	(56,964)		(54,641)
Adjustments [Member]
Revenue:
Other income	(44)		(53)
Total revenue	(44)		(53)
Expenses:
Commissions, premium taxes, and non-deferred acquisition costs	(44)		(53)
Total benefits and expenses	(44)		(53)
Subtotal	0		0
Nonoperating items	0		0
Measure of segment profitability (pretax)	$ 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.