CONSOLIDATED QUARTERLY RESULTS - UNAUDITED (Details) (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
CONSOLIDATED QUARTERLY RESULTS - UNAUDITED
Premiums and policy fees	$ 717,948	$ 681,324	$ 707,720	$ 692,398	$ 716,245	$ 693,161	$ 712,472	$ 662,256	$ 2,799,390		$ 2,784,134	[1]	$ 2,609,357	[1]
Reinsurance ceded	(365,821)	(311,862)	(336,119)	(296,295)	(363,162)	(319,732)	(356,603)	(324,417)	(1,310,097)		(1,363,914)	[1]	(1,380,712)	[1]
Net of reinsurance ceded	352,127	369,462	371,601	396,103	353,083	373,429	355,869	337,839	1,489,293		1,420,220	[1]	1,228,645	[1]
Net investment income	460,784	446,374	438,648	443,532	445,780	445,928	434,425	427,311	1,789,338		1,753,444	[1]	1,624,845	[1]
Realized investment gains (losses)	(44,085)	(2,686)	6,669	(13,022)	1,559	31,880	19,974	(7,986)	(53,124)		45,427	[1]	(27,382)	[1]
Other income	54,244	51,046	50,121	75,142	42,262	47,262	56,107	43,863	230,553		189,494	[1]	110,876	[1]
Total revenues	823,070	864,196	867,039	901,755	842,684	898,499	866,375	801,027	3,456,060		3,408,585	[1]	2,936,984	[1]
Total benefits and expenses	728,313	757,507	749,974	760,687	725,470	775,941	726,214	705,685	2,996,481		2,933,310	[1]	2,603,808	[1]
Income before income tax	94,757	106,689	117,065	141,068	117,214	122,558	140,161	95,342	459,579		475,275	[1]	333,176	[1]
Income tax expense	34,615	35,778	35,438	45,212	30,160	39,579	48,557	33,223	151,043		151,519	[1]	109,865	[1]
Net income	$ 60,142	$ 70,911	$ 81,627	$ 95,856	$ 87,054	$ 82,979	$ 91,604	$ 62,119	$ 308,536	[1]	$ 323,756	[1]	$ 223,311	[1]

[1] Recast from previously reported information