Accumulated Other Comprehensive Income (Loss) - Changes in AOCI, net of tax (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017		Jun. 30, 2016		Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, net of tax		$ 844,974	$ 1,094,557	$ 715,546		$ 686,616
OCI before reclassifications		185,718	464,638	374,541		1,023,195
Amounts reclassified from AOCI		(93,128)	(110,615)	(144,276)		(225,457)
Tax benefit (expense)		(16,399)	(39,993)	(24,646)		(75,767)
Comprehensive income (loss)		76,191	314,030	205,619		721,971
Ending balance, net of tax		921,165	1,408,587	921,165		1,408,587
Change in adjustments related to future policy benefit reserves, net of tax		(3,437)	(8,727)	(8,569)		(25,762)
Unrealized gains (losses) on investments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, net of tax		816,882	1,226,295	730,429	[1]	803,094	[1]
OCI before reclassifications		179,229	392,620	329,189	[1]	967,642	[1]
Amounts reclassified from AOCI		(94,591)	(112,377)	(147,146)	[1]	(229,491)	[1]
Tax benefit (expense)		(8,228)	(31,460)	(19,180)	[1]	(66,167)	[1]
Comprehensive income (loss)		76,410	248,783	162,863	[1]	671,984	[1]
Ending balance, net of tax	[1]	893,292	1,475,078	893,292		1,475,078
Cumulative impact of net unrealized gains losses on future policy benefit reserve		203,500		203,500				$ 212,100
Change in adjustments related to future policy benefit reserves, net of tax				(8,600)
OTTI losses recognized in AOCI
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, net of tax		(49,510)	(55,235)	(50,952)		(57,502)
OCI before reclassifications		0	0	0		0
Amounts reclassified from AOCI		1,511	1,810	2,966		4,121
Tax benefit (expense)		(14)	42	(27)		(2)
Comprehensive income (loss)		1,497	1,852	2,939		4,119
Ending balance, net of tax		(48,013)	(53,383)	(48,013)		(53,383)
Foreign currency translation adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, net of tax		100,908	(52,942)	58,970		(36,503)
OCI before reclassifications		7,028	71,918	46,232		56,502
Amounts reclassified from AOCI		0	0	0		0
Tax benefit (expense)		(8,120)	(8,575)	(5,386)		(9,598)
Comprehensive income (loss)		(1,092)	63,343	40,846		46,904
Ending balance, net of tax		99,816	10,401	99,816		10,401
Underfunded pension liability
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, net of tax		(25,244)	(25,690)	(24,887)		(24,641)
OCI before reclassifications		(539)	100	(880)		(949)
Amounts reclassified from AOCI		0	0	0		0
Tax benefit (expense)		(37)	0	(53)		0
Comprehensive income (loss)		(576)	100	(933)		(949)
Ending balance, net of tax		(25,820)	(25,590)	(25,820)		(25,590)
Cash flow hedge
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, net of tax		1,938	2,129	1,986		2,168
OCI before reclassifications		0	0	0		0
Amounts reclassified from AOCI		(48)	(48)	(96)		(87)
Tax benefit (expense)		0	0	0		0
Comprehensive income (loss)		(48)	(48)	(96)		(87)
Ending balance, net of tax		$ 1,890	$ 2,081	$ 1,890		$ 2,081

[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. At December 31, 2016, the cumulative impact of the Shadow Adjustments was $212.1 million. During the six months ended June 30, 2017, net movements of $(8.6) million were recorded, resulting in a total cumulative net impact of Shadow Adjustments on future policy benefit reserves of $203.5 million at June 30, 2017.