Investments - Funds Held (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Funds Held, Directly Managed [Abstract]
Funds held - directly managed	$ 1,187,552	$ 1,198,154
Net unrealized gains (losses):
Funds held by reinsured companies	408,735	321,267
Funds held - Directly Managed - Fair Value Option
Funds Held, Directly Managed [Abstract]
Fixed maturity investments, trading	191,297	176,937
Funds Held, Directly Managed, Fixed-Maturity Investment Components [Abstract]
Fixed maturity investments, at amortized cost	185,859	179,670
Net unrealized gains (losses):
Change in fair value - fair value option accounting	5,438	(2,733)
Change in fair value - embedded derivative accounting	0	0
Fixed maturity investments, trading	191,297	176,937
Funds held - Directly Managed - Variable Return
Funds Held, Directly Managed [Abstract]
Fixed maturity investments, trading	982,048	1,006,437
Funds Held, Directly Managed, Fixed-Maturity Investment Components [Abstract]
Fixed maturity investments, at amortized cost	940,194	1,044,377
Net unrealized gains (losses):
Change in fair value - fair value option accounting	0	0
Change in fair value - embedded derivative accounting	41,854	(37,940)
Fixed maturity investments, trading	982,048	1,006,437
Funds Held - Directly Managed
Funds Held, Directly Managed [Abstract]
Fixed maturity investments, trading	1,173,345	1,183,374
Other assets	14,207	14,780
Funds held - directly managed	1,187,552	1,198,154
Funds Held, Directly Managed, Fixed-Maturity Investment Components [Abstract]
Fixed maturity investments, at amortized cost	1,126,053	1,224,047
Net unrealized gains (losses):
Change in fair value - fair value option accounting	5,438	(2,733)
Change in fair value - embedded derivative accounting	41,854	(37,940)
Fixed maturity investments, trading	$ 1,173,345	$ 1,183,374

Debt Securities, Trading, Unrealized Gain (Loss), Embedded Derivative

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Debt Securities, Trading, Unrealized Gain (Loss), Fair Value Option

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Funds Held, Directly Managed [Abstract]

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Funds Held, Directly Managed, Fixed-Maturity Investment Components [Abstract]

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Funds Held, Directly Managed, Other Assets

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Funds Held under Reinsurance Agreements, Directly Managed, Net Asset

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Amount of the reinsurer's funds held on its behalf by the ceding insurer, including funds held in trust, under reinsurance treaties or contracts with the assuming insurer as security for the payment of the obligations thereunder.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.2,10)
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Amount of investment in debt security measured at fair value with change in fair value recognized in net income (trading).

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
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-Section 45
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Amortized cost of investments in debt securities classified as trading.

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