Reconciliation of Segment Operating Information to Consolidated Statement of Operations (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Segment Reporting Information [Line Items]
Premium	$ 732,545	$ 699,860	$ 705,582	$ 718,475	$ 653,542	$ 650,525	$ 672,350	$ 679,901	$ 2,856,462		$ 2,656,318		$ 2,651,758
Net investment income	174,947	169,400	175,176	174,121	174,786	173,491	173,104	171,647	693,644		693,028		676,364
Other income									1,577		2,151		2,170
Total revenue									3,551,683		3,351,497		3,330,292
Policy benefits	479,109	479,119	484,807	512,647	435,681	438,774	454,694	464,127	1,955,682		1,793,276		1,793,044
Required interest on policy reserves									0		0		0
Required interest on deferred acquisition costs									0		0		0
Amortization of acquisition costs	98,052	94,016	96,601	96,498	90,557	89,899	91,664	92,463	385,167		364,583		362,390
Commissions, premium taxes, and non-deferred acquisition costs									203,986		216,216		209,827
Insurance administrative expense									165,405	[1]	178,989	[1]	155,615	[1]
Parent expense									11,166		7,693		8,809
Stock-based compensation expense									21,605		14,954		11,848
Interest expense									80,512		77,908		75,529
Total benefits and expense									2,823,523		2,653,619		2,617,062
Sub total									728,160		697,878		713,230
Non operating items									2,944		19,880
Amortization of low-income housing interests									22,488	[2]	14,277	[2]	9,153	[3]
Measure of segment profitability (pretax)									753,592		732,035		722,383
Deduct applicable income taxes									(246,945)		(238,335)		(242,558)
Segment profits after tax									506,647		493,700		479,825
Add back income taxes applicable to segment profitabi									246,945		238,335		242,558
Add (deduct) realized investment gains (losses)	20,883	7,283	4,661	5,006	4,755	12,600	31,272	(22,723)	37,833		25,904		37,340
Deduct amortization of low-income housing									(22,488)	[2]	(14,277)	[2]	(9,153)	[3]
Deduct state administrative settlement expense											(6,901)	[4]
Deduct Family Heritage Life acquisition expenses									(2,944)	[5]
Deduct loss on sale of equipment											(979)	[6]
Deduct litigation expense											(12,000)	[7]
Income from continuing operations before income taxes	220,587	188,791	186,380	170,235	177,090	190,123	209,052	147,517	765,993		723,782		750,570
Life Insurance
Segment Reporting Information [Line Items]
Premium									1,808,524		1,726,244		1,663,699
Total revenue									1,808,524		1,726,244		1,663,699
Policy benefits									1,172,020		1,118,909		1,082,423
Required interest on policy reserves									(483,892)		(458,029)		(434,319)
Required interest on deferred acquisition costs									163,875		159,886		154,473
Amortization of acquisition costs									309,930		292,168		289,068
Commissions, premium taxes, and non-deferred acquisition costs									137,115		152,347		141,792
Total benefits and expense									1,299,048		1,265,281		1,233,437
Sub total									509,476		460,963		430,262
Measure of segment profitability (pretax)									509,476		460,963		430,262
Health Insurance
Segment Reporting Information [Line Items]
Premium									1,047,783		930,493		987,937
Total revenue									1,047,783		930,493		987,937
Policy benefits									739,945		632,847		669,707
Required interest on policy reserves									(40,963)		(36,729)		(35,368)
Required interest on deferred acquisition costs									19,059		18,883		19,758
Amortization of acquisition costs									65,278		62,345		66,309
Commissions, premium taxes, and non-deferred acquisition costs									67,123		64,157		68,565
Total benefits and expense									850,442		741,503		788,971
Sub total									197,341		188,990		198,966
Measure of segment profitability (pretax)									197,341		188,990		198,966
Annuity
Segment Reporting Information [Line Items]
Premium									559		608		638
Total revenue									559		608		638
Policy benefits									44,121		42,547		41,430
Required interest on policy reserves									(59,293)		(57,040)		(51,996)
Required interest on deferred acquisition costs									2,238		2,618		2,709
Amortization of acquisition costs									9,959		10,070		7,013
Commissions, premium taxes, and non-deferred acquisition costs									69		68		134
Total benefits and expense									(2,906)		(1,737)		(710)
Sub total									3,465		2,345		1,348
Measure of segment profitability (pretax)									3,465		2,345		1,348
Investment
Segment Reporting Information [Line Items]
Net investment income									715,918		707,041		685,253
Total revenue									715,918		707,041		685,253
Required interest on policy reserves									584,148		551,798		521,683
Required interest on deferred acquisition costs									(185,172)		(181,387)		(176,940)
Interest expense									80,298		77,644		75,265
Total benefits and expense									479,274		448,055		420,008
Sub total									236,644		258,986		265,245
Measure of segment profitability (pretax)									236,644		258,986		265,245
All Other Segments
Segment Reporting Information [Line Items]
Other income									1,898		2,507		2,834
Total revenue									1,898		2,507		2,834
Insurance administrative expense									165,405	[1]	159,109	[1]	155,615	[1]
Total benefits and expense									165,405		159,109		155,615
Sub total									(163,507)		(156,602)		(152,781)
Measure of segment profitability (pretax)									(163,507)		(156,602)		(152,781)
Corporate
Segment Reporting Information [Line Items]
Parent expense									8,222		7,693		8,809
Stock-based compensation expense									21,605		14,954		11,848
Total benefits and expense									29,827		22,647		20,657
Sub total									(29,827)		(22,647)		(20,657)
Measure of segment profitability (pretax)									(29,827)		(22,647)		(20,657)
Adjustments
Segment Reporting Information [Line Items]
Premium									(404)	[8]	(1,027)	[8]	(516)	[8]
Net investment income									(22,274)	[2],[9]	(14,013)	[2],[9]	(8,889)	[3],[9]
Other income									(321)	[10]	(356)	[10]	(664)	[10]
Total revenue									(22,999)		(15,396)		(10,069)
Policy benefits									(404)	[8]	(1,027)	[8]	(516)	[8]
Commissions, premium taxes, and non-deferred acquisition costs									(321)	[10]	(356)	[10]	(664)	[10]
Insurance administrative expense											19,880	[1],[4],[6],[7]
Parent expense									2,944	[5]
Interest expense									214	[9]	264	[9]	264	[9]
Total benefits and expense									2,433		18,761		(916)
Sub total									(25,432)		(34,157)		(9,153)
Non operating items									2,944	[5]	19,880	[4],[6],[7]
Amortization of low-income housing interests									22,488	[2]	14,277	[2]	9,153	[3]
Measure of segment profitability (pretax)									0		0		0
Deduct amortization of low-income housing									$ (22,488)	[2]	$ (14,277)	[2]	$ (9,153)	[3]

[1] Administrative expense is not allocated to insurance segments.

[2] Amortization of low-income housing interests.

[3] Amortization of low-income housing interests, previously considered a reduction of consolidated pretax segment profitability.

[4] State administrative settlement expense.

[5] Family Heritage Life acquisition expense.

[6] Loss on sale of equipment.

[7] Litigation expense.

[8] Medicare Part D items adjusted to GAAP from the segment analysis, which matches expected benefits with policy premium.

[9] Reclassification of interest amount due to accounting rule requiring deconsolidation of Trust Preferred Securities.

[10] Elimination of intersegment commission.