Segment Information (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012 item	Dec. 31, 2011	Dec. 31, 2010
Segment Information
Number of reportable segments	3
Revenue:
Premium income	$ 422,153	$ 523,216	$ 805,622
Fee income	535,823	486,795	447,954
Net investment income	1,191,551	1,158,486	1,174,744
Net realized gains (losses) on investments	116,717	24,495	(24,495)
Total revenues	2,266,244	2,192,992	2,403,825
Benefits and expenses:
Policyholder benefits	1,198,310	1,263,962	1,540,407
Operating expenses	694,515	632,975	597,657
Total benefits and expenses, net	1,892,825	1,896,937	2,138,064
Income (loss) from continuing operations before income taxes	373,419	296,055	265,761
Income tax expense (benefit)	135,305	93,818	68,627
Income from continuing operations	238,114	202,237	197,134
Assets
Investments	26,110,376	23,995,232
Other assets	2,069,650	1,846,183
Separate account assets	24,605,526	22,331,391
Assets of continuing operations	52,785,552	48,172,806
Assets of discontinued operations	33,053	39,621
Total assets	52,818,605	48,212,427
Individual Markets Segment
Revenue:
Premium income	314,350	395,923	676,395
Fee income	74,985	65,487	56,232
Net investment income	729,885	714,228	730,439
Net realized gains (losses) on investments	55,959	20,533	(1,239)
Total revenues	1,175,179	1,196,171	1,461,827
Benefits and expenses:
Policyholder benefits	882,726	937,885	1,218,791
Operating expenses	136,895	109,005	134,445
Total benefits and expenses, net	1,019,621	1,046,890	1,353,236
Income (loss) from continuing operations before income taxes	155,558	149,281	108,591
Income tax expense (benefit)	50,869	49,221	29,487
Income from continuing operations	104,689	100,060	79,104
Assets
Investments	14,797,517	13,702,356
Other assets	1,172,932	1,108,744
Separate account assets	6,363,214	5,884,676
Assets of continuing operations	22,333,663	20,695,776
Retirement Services Segment
Revenue:
Premium income	3,670	1,960	5,509
Fee income	456,052	416,405	387,103
Net investment income	414,114	399,222	399,456
Net realized gains (losses) on investments	60,726	3,311	(23,229)
Total revenues	934,562	820,898	768,839
Benefits and expenses:
Policyholder benefits	204,296	222,642	221,943
Operating expenses	492,427	435,149	401,117
Total benefits and expenses, net	696,723	657,791	623,060
Income (loss) from continuing operations before income taxes	237,839	163,107	145,779
Income tax expense (benefit)	78,150	50,869	34,547
Income from continuing operations	159,689	112,238	111,232
Assets
Investments	9,761,036	8,752,301
Other assets	773,712	610,971
Separate account assets	18,242,312	16,446,714
Assets of continuing operations	28,777,060	25,809,986
Other Segment
Revenue:
Premium income	104,133	125,333	123,718
Fee income	4,786	4,903	4,619
Net investment income	47,552	45,036	44,849
Net realized gains (losses) on investments	32	651	(27)
Total revenues	156,503	175,923	173,159
Benefits and expenses:
Policyholder benefits	111,288	103,435	99,673
Operating expenses	65,193	88,821	62,095
Total benefits and expenses, net	176,481	192,256	161,768
Income (loss) from continuing operations before income taxes	(19,978)	(16,333)	11,391
Income tax expense (benefit)	6,286	(6,272)	4,593
Income from continuing operations	(26,264)	(10,061)	6,798
Assets
Investments	1,551,823	1,540,575
Other assets	123,006	126,468
Assets of continuing operations	$ 1,674,829	$ 1,667,043