Schedule II - Condensed Financial Information Of Registrant (Condensed Statements 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
Condensed Financial Statements, Captions [Line Items]
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
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
Total revenue	928,698	877,100	885,795	897,923	833,554	837,241	877,334	829,272	3,589,516	3,377,401	3,367,632
General operating expenses									198,176	201,636	176,272
Interest expense									80,512	77,908	75,529
Total benefits and expense									2,823,523	2,653,619	2,617,062
Operating income (loss) before income taxes and equity in earnings of affiliates	220,587	188,791	186,380	170,235	177,090	190,123	209,052	147,517	765,993	723,782	750,570
Income taxes									236,669	226,166	246,475
Net income	150,987	130,672	128,988	118,677	122,839	131,400	142,781	100,141	529,324	497,161	498,866
Parent Company
Condensed Financial Statements, Captions [Line Items]
Net investment income									22,968	23,542	26,031
Realized investment gains (losses)									(3,534)	508	(1,646)
Total revenue									19,434	24,050	24,385
General operating expenses									49,549	30,945	21,682
Reimbursements from affiliates									(31,184)	(19,335)	(13,375)
Interest expense									81,145	75,426	74,827
Total benefits and expense									99,510	87,036	83,134
Operating income (loss) before income taxes and equity in earnings of affiliates									(80,076)	(62,986)	(58,749)
Income taxes									24,916	14,380	18,521
Net operating loss before equity in earnings of affiliates									(55,160)	(48,606)	(40,228)
Equity in earnings of affiliates									584,484	545,767	539,094
Net income									$ 529,324	$ 497,161	$ 498,866