Accumulated Other Comprehensive Income (Loss) - Details About AOCI Components (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Total before tax		$ 14,540	$ (51,147)
Provision (benefit) for income tax		(31,902)	(13,092)
Unrealized gains (losses) on investments
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Total before tax	[1]	10,875	(52,554)
OTTI losses recognized in AOCI
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Total before tax		3,713	1,455
Cash flow hedge
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Total before tax		(48)	(48)
Accumulated Foreign Currency Adjustment Attributable to Parent [Member]
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Total before tax		0	0
Underfunded pension liability
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Total before tax		0	0
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Total before tax		14,540	(51,147)
Provision (benefit) for income tax		(2,099)	(487)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		12,441	(51,634)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Unrealized gains (losses) on investments
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Net realized gains (losses) on investments AFS		17,762	(47,020)
OTTI on investments transferred to (from) OCI		2,848	6,874
Reclassification adjustment for investments transferred to equity method		0	0
Total before tax		10,875	(52,554)
Provision (benefit) for income tax		(2,002)	(474)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		8,873	(53,028)
Reclassification out of Accumulated Other Comprehensive Income [Member] | OTTI losses recognized in AOCI
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Net realized gains (losses) on investments AFS		3,552	1,455
OTTI on investments transferred to (from) OCI		161	0
Total before tax		3,713	1,455
Provision (benefit) for income tax		(97)	(13)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		3,616	1,442
Reclassification out of Accumulated Other Comprehensive Income [Member] | Cash flow hedge
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Total before tax		(48)	(48)
Provision (benefit) for income tax		0	0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		(48)	(48)
Life Funds Withheld Assets
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
OTTI on investments transferred to (from) OCI		(1,203)	0
Life Funds Withheld Assets | Reclassification out of Accumulated Other Comprehensive Income [Member] | Unrealized gains (losses) on investments
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Change in adjustments related to future policy benefit reserves, net of tax		$ (9,735)	$ (12,408)

[1] For certain annuity contracts that are subject to the GreyCastle Life Retro Arrangements, future 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, 2017, the cumulative impact of the Shadow Adjustments was $184.9 million. During the three months ended March 31, 2018, net movements of $(4.2) million were recorded, resulting in a total cumulative net impact of Shadow Adjustments on future policy benefit reserves of $180.8 million at March 31, 2018.