Business Segments - Analysis of Profitability by Segment (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016		Mar. 31, 2015
Segment Reporting Information [Line Items]
Pretax operating income	$ 195,155		$ 194,358
Applicable taxes	(61,771)		(63,657)
Segment profits after tax	133,384		130,701
Discontinued operations (after tax)	(9,541)		(9,130)
After-tax total, after discontinued operations	123,843		121,571
Pretax operating income, change	797
Applicable taxes, change	1,886
After-tax total, before discontinued operations, change	2,683
Discontinued operations (after tax), change	(411)
Total, change	$ 2,272
Pretax operating income, % change	0.00%
Applicable taxes, % change	(3.00%)
After-tax total, before discontinued operations, % change	2.00%
Discontinued operations (after tax), % change	5.00%
Total, % change	2.00%
Reconciling items, net of tax:
Realized gains (losses)-Investments	$ 190		77
Net income	124,033	[1]	121,648	[2]
Realized gains (losses) - Investments, change	113
Net income, change	$ 2,385
Net income, % change	2.00%
Operating Segments [Member] | Life insurance underwriting margin [Member]
Segment Reporting Information [Line Items]
Pretax operating income	$ 144,300		141,403
Pretax operating income, change	$ 2,897
Pretax operating income, % change	2.00%
Operating Segments [Member] | Health insurance underwriting margin [Member]
Segment Reporting Information [Line Items]
Pretax operating income	$ 51,515		51,577
Pretax operating income, change	$ (62)
Pretax operating income, % change	0.00%
Operating Segments [Member] | Annuity underwriting margin [Member]
Segment Reporting Information [Line Items]
Pretax operating income	$ 1,631		1,093
Pretax operating income, change	$ 538
Pretax operating income, % change	49.00%
Operating Segments [Member] | Excessive investment income [Member]
Segment Reporting Information [Line Items]
Pretax operating income	$ 54,673		54,926
Pretax operating income, change	$ (253)
Pretax operating income, % change	0.00%
Operating Segments [Member] | Other and corporate [Member]
Segment Reporting Information [Line Items]
Pretax operating income	$ (56,964)		(54,641)
Operating Segments [Member] | Other and corporate [Member] | Other income [Member]
Segment Reporting Information [Line Items]
Pretax operating income	465		722
Pretax operating income, change	$ (257)
Pretax operating income, % change	(36.00%)
Operating Segments [Member] | Other and corporate [Member] | Administrative expense [Member]
Segment Reporting Information [Line Items]
Pretax operating income	$ (48,468)		(45,951)
Pretax operating income, change	$ (2,517)
Pretax operating income, % change	5.00%
Operating Segments [Member] | Other and corporate [Member] | Corporate [Member]
Segment Reporting Information [Line Items]
Pretax operating income	$ (8,961)		$ (9,412)
Pretax operating income, change	$ 451
Pretax operating income, % change	(5.00%)

[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.