Segment Information (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Revenue:
Premium income	$ 446,395	$ 464,093	$ 422,153
Fee income	729,179	618,244	535,823
Other revenue	7,506	7,355	0
Net investment income	1,228,388	1,091,389	1,191,551
Realized investments gains (losses), net	147,371	(14,136)	116,717
Total revenues	2,558,839	2,166,945	2,266,244
Benefits and expenses:
Policyholder benefits	1,222,445	1,232,091	1,198,310
Operating expenses	863,122	747,321	694,515
Total benefits and expenses	2,085,567	1,979,412	1,892,825
Income (loss) before income taxes	473,272	187,533	373,419
Income tax expense (benefit)	155,903	58,791	135,305
Net income (loss)	317,369	128,742	238,114
Assets:
Investments	28,323,243	26,516,423
Other assets	2,281,808	2,147,193
Separate account assets	27,718,844	26,630,904
Assets of continuing operations	58,323,895	55,294,520
Assets of discontinued operations	24,324	29,007
Total assets	58,348,219	55,323,527
Individual Markets Segment
Revenue:
Premium income	360,305	354,202	314,350
Fee income	95,631	94,037	74,985
Other revenue	0	7,355
Net investment income	748,015	688,279	729,885
Realized investments gains (losses), net	44,381	19,071	55,959
Total revenues	1,248,332	1,162,944	1,175,179
Benefits and expenses:
Policyholder benefits	902,982	921,096	882,726
Operating expenses	136,850	142,141	136,895
Total benefits and expenses	1,039,832	1,063,237	1,019,621
Income (loss) before income taxes	208,500	99,707	155,558
Income tax expense (benefit)	68,719	34,265	50,869
Net income (loss)	139,781	65,442	104,689
Assets:
Investments	15,928,591	14,563,978
Other assets	1,283,256	1,179,332
Separate account assets	7,247,463	6,321,135
Assets of continuing operations	24,459,310	22,064,445
Retirement Services Segment
Revenue:
Premium income	1,215	3,954	3,670
Fee income	629,533	519,842	456,052
Other revenue	7,506	0
Net investment income	426,340	351,729	414,114
Realized investments gains (losses), net	102,597	(33,233)	60,726
Total revenues	1,167,191	842,292	934,562
Benefits and expenses:
Policyholder benefits	206,339	196,115	204,296
Operating expenses	647,165	538,209	492,427
Total benefits and expenses	853,504	734,324	696,723
Income (loss) before income taxes	313,687	107,968	237,839
Income tax expense (benefit)	104,162	33,240	78,150
Net income (loss)	209,525	74,728	159,689
Assets:
Investments	10,621,831	10,370,421
Other assets	855,728	839,755
Separate account assets	20,471,381	20,309,769
Assets of continuing operations	31,948,940	31,519,945
Other Segment
Revenue:
Premium income	84,875	105,937	104,133
Fee income	4,015	4,365	4,786
Other revenue	0	0
Net investment income	54,033	51,381	47,552
Realized investments gains (losses), net	393	26	32
Total revenues	143,316	161,709	156,503
Benefits and expenses:
Policyholder benefits	113,124	114,880	111,288
Operating expenses	79,107	66,971	65,193
Total benefits and expenses	192,231	181,851	176,481
Income (loss) before income taxes	(48,915)	(20,142)	(19,978)
Income tax expense (benefit)	(16,978)	(8,714)	6,286
Net income (loss)	(31,937)	(11,428)	(26,264)
Assets:
Investments	1,772,821	1,582,024
Other assets	142,824	128,106
Assets of continuing operations	$ 1,915,645	$ 1,710,130