Business Segments - Analysis of Profitability by Segment (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Segment Reporting Information [Line Items]
Pretax operating income	$ 197,489	$ 195,155
Applicable taxes	(58,818)	(61,771)
Segment profits after tax	138,671	133,384
Discontinued operations (after tax)	(3,637)	(9,541)
Net operating income	135,034	123,843
Reconciling items, net of tax:
Realized gains (losses)—investments (after tax)	(1,493)	190
Net income	133,541	124,033
Operating Segments [Member] | Life insurance underwriting margin [Member]
Segment Reporting Information [Line Items]
Pretax operating income	144,104	144,300
Operating Segments [Member] | Health insurance underwriting margin [Member]
Segment Reporting Information [Line Items]
Pretax operating income	53,377	51,515
Operating Segments [Member] | Annuity underwriting margin [Member]
Segment Reporting Information [Line Items]
Pretax operating income	2,610	1,631
Operating Segments [Member] | Excessive investment income [Member]
Segment Reporting Information [Line Items]
Pretax operating income	59,288	54,673
Operating Segments [Member] | Other and corporate [Member]
Segment Reporting Information [Line Items]
Pretax operating income	(61,890)	(56,964)
Operating Segments [Member] | Other and corporate [Member] | Other income [Member]
Segment Reporting Information [Line Items]
Pretax operating income	451	465
Operating Segments [Member] | Other and corporate [Member] | Administrative expense [Member]
Segment Reporting Information [Line Items]
Pretax operating income	(51,913)	(48,468)
Operating Segments [Member] | Other and corporate [Member] | Corporate and adjustments [Member]
Segment Reporting Information [Line Items]
Pretax operating income	$ (10,428)	$ (8,961)