Accumulated Other Comprehensive Income (Loss) - Changes in AOCI, net of tax (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, net of tax		$ 1,408,587	$ 1,076,174	$ 686,616	$ 1,484,458
OCI before reclassifications		252,673	(28,508)	1,275,869	(322,827)
Amounts reclassified from AOCI		(149,032)	(92,063)	(374,490)	(242,696)
Tax benefit (expense)		7,577	(521)	(68,190)	36,147
Comprehensive income (loss)		111,218	(121,092)	833,189	(529,376)
Ending balance, net of tax		1,519,805	955,082	1,519,805	955,082
Change in adjustments related to future policy benefit reserves, net of tax		(2,058)	(40,681)	(27,820)	(127,365)
Unrealized gains (losses) on investments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, net of tax	[1]	1,475,078	1,168,964	803,094	1,590,114
OCI before reclassifications	[1]	203,451	(4,334)	1,171,094	(294,341)
Amounts reclassified from AOCI	[1]	(150,482)	(94,393)	(379,974)	(256,731)
Tax benefit (expense)	[1]	8,600	(2,213)	(57,567)	28,982
Comprehensive income (loss)	[1]	61,569	(100,940)	733,553	(522,090)
Ending balance, net of tax	[1]	1,536,647	1,068,024	1,536,647	1,068,024
Cumulative impact of net unrealized gains losses on future policy benefit reserve		246,600		246,600		$ 274,400
Change in adjustments related to future policy benefit reserves, net of tax				(27,800)
OTTI losses recognized in AOCI
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, net of tax		(53,383)	(64,614)	(57,502)	(76,047)
OCI before reclassifications		0	0	0	0
Amounts reclassified from AOCI		1,497	2,318	5,618	13,916
Tax benefit (expense)		(36)	(181)	(38)	(346)
Comprehensive income (loss)		1,461	2,137	5,580	13,570
Ending balance, net of tax		(51,922)	(62,477)	(51,922)	(62,477)
Foreign currency translation adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, net of tax		10,401	(9,508)	(36,503)	(11,188)
OCI before reclassifications		45,185	(24,267)	101,687	(28,225)
Amounts reclassified from AOCI		0	0	0	0
Tax benefit (expense)		(987)	1,873	(10,585)	7,511
Comprehensive income (loss)		44,198	(22,394)	91,102	(20,714)
Ending balance, net of tax		54,599	(31,902)	54,599	(31,902)
Underfunded pension liability
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, net of tax		(25,590)	(21,143)	(24,641)	(20,789)
OCI before reclassifications		4,037	93	3,088	(261)
Amounts reclassified from AOCI		0	0	0	0
Tax benefit (expense)		0	0	0	0
Comprehensive income (loss)		4,037	93	3,088	(261)
Ending balance, net of tax		(21,553)	(21,050)	(21,553)	(21,050)
Cash flow hedge
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, net of tax		2,081	2,475	2,168	2,368
OCI before reclassifications		0	0	0	0
Amounts reclassified from AOCI		(47)	12	(134)	119
Tax benefit (expense)		0	0	0	0
Comprehensive income (loss)		(47)	12	(134)	119
Ending balance, net of tax		$ 2,034	$ 2,487	$ 2,034	$ 2,487

[1] For certain annuity contracts that are subject to the GreyCastle Life Retro Arrangements, policy benefit reserves were historically increased for the impact of changes in unrealized gains on investments supporting such contracts as if the gains had been realized, with a corresponding entry to other comprehensive income ("Shadow Adjustments"). Upon completion of the GreyCastle Life Retro Arrangements, no further Shadow Adjustments were recorded. As of December 31, 2015, the cumulative impact of the Shadow Adjustments was $274.4 million. During the nine months ended September 30, 2016, net movements of $(27.8) million were recorded, resulting in a total cumulative net impact of Shadow Adjustments on future policy benefit reserves of $246.6 million as of September 30, 2016.