CONSOLIDATED QUARTERLY RESULTS - UNAUDITED (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
CONSOLIDATED QUARTERLY RESULTS - UNAUDITED
Premiums and policy fees	$ 867,263	$ 755,300	$ 848,183	$ 812,323	$ 837,706	$ 653,664	$ 752,752	$ 723,200	$ 3,283,069	$ 2,967,322	$ 2,799,390
Reinsurance ceded	(430,878)	(283,104)	(348,255)	(333,506)	(387,192)	(277,628)	(396,777)	(325,840)	(1,395,743)	(1,387,437)	(1,310,097)
Net of reinsurance ceded	436,385	472,196	499,928	478,817	450,514	376,036	355,975	397,360	1,887,326	1,579,885	1,489,293
Net investment income	525,539	532,861	525,576	514,037	515,340	434,772	447,064	439,012	2,098,013	1,836,188	1,789,338
Realized investment gains (losses)	71,869	39,299	42,386	30,981	(13,227)	4,263	(47,636)	(5,223)	184,535	(61,823)	(53,124)
Other income	85,119	72,404	71,296	65,514	69,825	65,523	60,638	54,434	294,333	250,420	230,553
Total revenues	1,118,912	1,116,760	1,139,186	1,089,349	1,022,452	880,594	816,041	885,583	4,464,207	3,604,670	3,456,060
Total benefits and expenses	888,469	932,640	966,571	937,738	902,049	767,239	737,114	775,769	3,725,418	3,182,171	2,996,481
Income before income tax	230,443	184,120	172,615	151,611	120,403	113,355	78,927	109,814	738,789	422,499	459,579
Income tax expense	78,917	62,287	56,572	49,062	31,931	37,107	25,923	35,936	246,838	130,897	151,043
Net income	$ 151,526	$ 121,833	$ 116,043	$ 102,549	$ 88,472	$ 76,248	$ 53,004	$ 73,878	$ 491,951	$ 291,602	$ 308,536