Business Segments - Analysis of Profitability by Segment (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014		Dec. 31, 2013
Segment Reporting Information [Line Items]
Pretax operating income									$ 776,372	$ 771,644		$ 756,086
Applicable taxes									(253,459)	(252,041)		(246,686)
Segment profits after tax									522,913	519,603		509,400
Discontinued operations (after tax)(1)									10,807	14,865		21,267
Total									533,720	534,468		530,667
Realized gains (losses)—investments (after tax)									(5,714)	15,306		3,965
Family Heritage acquisition finalization adjustments (after tax)									0	0		522
Legal settlement expenses (after tax)									0	(1,519)		(5,931)
Guaranty Fund assessment (after tax)									0	0		(751)
Administrative settlements (after tax)									(906)	(5,316)		0
Net income	$ 132,956	$ 145,386	$ 127,110	$ 121,648	$ 146,748	$ 132,412	$ 130,923	$ 132,856	527,100	542,939	[1],[2]	528,472	[1],[2]
Pretax operating income, Change									4,728	15,558
Applicable taxes, Change									(1,418)	(5,355)
Net operating income, Change									3,310	10,203
Discontinued operation (after tax), Change									(4,058)	(6,402)
Total, Change									(748)	3,801
Realized gains (losses)-investments (after tax), Change									(21,020)	11,341
Family Heritage acquisition finalization adjustments (after tax), Change									0	(522)
Legal settlement expenses (after tax), Change									1,519	4,412
Guaranty Fund assessment (after tax), Change									0	751
Administrative settlements (after tax), Change									4,410	(5,316)
Net income, Change									$ (15,839)	$ 14,467
Pretax operating income, Change %									1.00%	2.00%
Applicable taxes, Change %									1.00%	2.00%
Net operating income, Change %									1.00%	2.00%
Discontinued operation (after tax), Change %									(27.00%)	(30.00%)
Total, Change %									0.00%	1.00%
Net income, Change %									(3.00%)	3.00%
Operating Segments [Member] | Life insurance underwriting margin [Member]
Segment Reporting Information [Line Items]
Pretax operating income									$ 569,402	$ 556,489		545,059
Pretax operating income, Change									$ 12,913	$ 11,430
Pretax operating income, Change %									2.00%	2.00%
Operating Segments [Member] | Health insurance underwriting margin [Member]
Segment Reporting Information [Line Items]
Pretax operating income									$ 204,377	$ 199,319		196,507
Pretax operating income, Change									$ 5,058	$ 2,812
Pretax operating income, Change %									3.00%	1.00%
Operating Segments [Member] | Annuity underwriting margin [Member]
Segment Reporting Information [Line Items]
Pretax operating income									$ 4,568	$ 4,312		3,939
Pretax operating income, Change									$ 256	$ 373
Pretax operating income, Change %									6.00%	9.00%
Operating Segments [Member] | Excess investment income [Member]
Segment Reporting Information [Line Items]
Pretax operating income									$ 219,504	$ 224,364		218,161
Pretax operating income, Change									$ (4,860)	$ 6,203
Pretax operating income, Change %									(2.00%)	3.00%
Operating Segments [Member] | Other insurance [Member]
Segment Reporting Information [Line Items]
Pretax operating income									$ (183,812)	$ (172,478)		(173,443)
Operating Segments [Member] | Other insurance [Member] | Other income [Member]
Segment Reporting Information [Line Items]
Pretax operating income									2,379	2,354		2,208
Pretax operating income, Change									$ 25	$ 146
Pretax operating income, Change %									1.00%	7.00%
Operating Segments [Member] | Other insurance [Member] | Administrative expense [Member]
Segment Reporting Information [Line Items]
Pretax operating income									$ (186,191)	$ (174,832)		(175,651)
Pretax operating income, Change									$ (11,359)	$ 819
Pretax operating income, Change %									6.00%	0.00%
Operating Segments [Member] | Other insurance [Member] | Corporate and adjustments [Member]
Segment Reporting Information [Line Items]
Pretax operating income									$ (37,667)	$ (40,362)		$ (34,137)
Pretax operating income, Change									$ 2,695	$ (6,225)
Pretax operating income, Change %									(7.00%)	18.00%

[1] Certain balances were adjusted to give effect to discontinued operations and the adoption of new accounting guidance as described in Note 1- Significant Accounting Policies under the caption "Low-Income Housing Tax Credit Interests."

[2] Certain balances were adjusted to give effect to discontinued operations as described in Note 1—Significant Accounting Policies.