Business Segments - Reconciliation of Revenues and Operations by Segment to Major Income Statement Line Items (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Segment Reporting Information [Line Items]
Premium	$ 750,611	$ 750,998	$ 765,851	$ 784,814	$ 732,545	$ 699,860	$ 705,582	$ 718,475	$ 3,052,274	$ 2,856,462	$ 2,656,318
Net investment income	178,284	176,656	177,964	176,839	174,947	169,400	175,176	174,121	709,743	693,644	693,028
Other income									1,931	1,577	2,151
Total revenue									3,763,948	3,551,683	3,351,497
Policy benefits	495,561	516,783	524,499	552,003	479,109	479,119	484,807	512,647	2,088,846	1,955,682	1,793,276
Required interest on policy reserves									0	0	0
Required interest on deferred acquisition costs									0	0	0
Acquisition expense and adjustments	100,743	98,444	102,488	101,714	98,052	94,016	96,601	96,498	403,389	385,167	364,583
Commissions, premium taxes, and non-deferred acquisition costs									221,426	203,986	216,216
Insurance administrative expense									180,053	165,405	178,989
Parent expense									8,995	11,166	7,693
Stock-based compensation expense									25,642	21,605	14,954
Interest expense									80,461	80,512	77,908
Total benefits and expenses									3,008,812	2,823,523	2,653,619
Sub total									755,136	728,160	697,878
Non operating items									8,761	2,944	19,880
Amortization of low-income housing interests									24,907	22,488	14,277
Measure of segment profitability (pretax)									788,804	753,592	732,035
Deduct applicable income taxes									(258,137)	(246,945)	(238,335)
Segment profits after tax									530,667	506,647	493,700
Add back income taxes applicable to segment profitability									258,137	246,945	238,335
Add (deduct) realized investment gains (losses)	1,525	4,459	5,913	(3,907)	20,883	7,283	4,661	5,006	7,990	37,833	25,904
Deduct amortization of low-income housing									(24,907)	(22,488)	(14,277)
Deduct state administrative settlement expense											(6,901)
Deduct Guaranty Fund Assessment									(1,155)
Acquisition expense and adjustments										(2,944)
Deduct loss on sale of equipment											(979)
Deduct legal settlement expenses									(9,125)		(12,000)
Operating income (loss) before income taxes and equity in earnings of affiliates	206,429	190,850	192,784	173,063	220,587	188,791	186,380	170,235	763,126	765,993	723,782
Family Heritage [Member]
Segment Reporting Information [Line Items]
Acquisition expense and adjustments									1,519
Acquisition expense and adjustments										(2,900)
Operating Segments [Member] | Life Insurance [Member]
Segment Reporting Information [Line Items]
Premium									1,885,332	1,808,524	1,726,244
Total revenue									1,885,332	1,808,524	1,726,244
Policy benefits									1,227,857	1,172,020	1,118,909
Required interest on policy reserves									(508,236)	(483,892)	(458,029)
Required interest on deferred acquisition costs									164,981	163,875	159,886
Acquisition expense and adjustments									323,950	309,930	292,168
Commissions, premium taxes, and non-deferred acquisition costs									131,721	137,115	152,347
Total benefits and expenses									1,340,273	1,299,048	1,265,281
Sub total									545,059	509,476	460,963
Measure of segment profitability (pretax)									545,059	509,476	460,963
Operating Segments [Member] | Health Insurance [Member]
Segment Reporting Information [Line Items]
Premium									1,163,826	1,047,783	930,493
Total revenue									1,163,826	1,047,783	930,493
Policy benefits									806,478	739,945	632,847
Required interest on policy reserves									(59,858)	(40,963)	(36,729)
Required interest on deferred acquisition costs									23,233	19,059	18,883
Acquisition expense and adjustments									72,244	65,278	62,345
Commissions, premium taxes, and non-deferred acquisition costs									89,922	67,123	64,157
Total benefits and expenses									932,019	850,442	741,503
Sub total									231,807	197,341	188,990
Measure of segment profitability (pretax)									231,807	197,341	188,990
Operating Segments [Member] | Annuity [Member]
Segment Reporting Information [Line Items]
Premium									532	559	608
Total revenue									532	559	608
Policy benefits									43,302	44,121	42,547
Required interest on policy reserves									(57,294)	(59,293)	(57,040)
Required interest on deferred acquisition costs									1,811	2,238	2,618
Acquisition expense and adjustments									8,714	9,959	10,070
Commissions, premium taxes, and non-deferred acquisition costs									60	69	68
Total benefits and expenses									(3,407)	(2,906)	(1,737)
Sub total									3,939	3,465	2,345
Measure of segment profitability (pretax)									3,939	3,465	2,345
Operating Segments [Member] | Investment [Member]
Segment Reporting Information [Line Items]
Net investment income									734,650	715,918	707,041
Total revenue									734,650	715,918	707,041
Required interest on policy reserves									625,388	584,148	551,798
Required interest on deferred acquisition costs									(190,025)	(185,172)	(181,387)
Interest expense									80,461	80,298	77,644
Total benefits and expenses									515,824	479,274	448,055
Sub total									218,826	236,644	258,986
Measure of segment profitability (pretax)									218,826	236,644	258,986
Operating Segments [Member] | Other [Member]
Segment Reporting Information [Line Items]
Other income									2,208	1,898	2,507
Total revenue									2,208	1,898	2,507
Insurance administrative expense									178,898	165,405	159,109
Total benefits and expenses									178,898	165,405	159,109
Sub total									(176,690)	(163,507)	(156,602)
Measure of segment profitability (pretax)									(176,690)	(163,507)	(156,602)
Corporate [Member]
Segment Reporting Information [Line Items]
Parent expense									8,495	8,222	7,693
Stock-based compensation expense									25,642	21,605	14,954
Total benefits and expenses									34,137	29,827	22,647
Sub total									(34,137)	(29,827)	(22,647)
Measure of segment profitability (pretax)									(34,137)	(29,827)	(22,647)
Adjustments [Member]
Segment Reporting Information [Line Items]
Premium									2,584	(404)	(1,027)
Net investment income									(24,907)	(22,274)	(14,013)
Other income									(277)	(321)	(356)
Total revenue									(22,600)	(22,999)	(15,396)
Policy benefits									11,209	(404)	(1,027)
Acquisition expense and adjustments									(1,519)
Commissions, premium taxes, and non-deferred acquisition costs									(277)	(321)	(356)
Insurance administrative expense									1,155		19,880
Parent expense									500	2,944
Interest expense										214	264
Total benefits and expenses									11,068	2,433	18,761
Sub total									(33,668)	(25,432)	(34,157)
Non operating items									8,761	2,944	19,880
Amortization of low-income housing interests									24,907	22,488	14,277
Measure of segment profitability (pretax)									0	0	0
Deduct amortization of low-income housing									$ (24,907)	$ (22,488)	$ (14,277)