Commitments and Contingencies - Concentrations of Credit Risk (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
Concentration Risk [Line Items]
Fixed maturities, at fair value	$ 12,786,380	$ 10,680,714
Provision for uncollectible premiums receivable	9,000	7,000
Funds Held under Reinsurance Agreements, Allowance for Credit loss	7,000	0
Deposit contracts, allowance for credit loss	2,000
Premium Receivable, Allowance for Credit Loss, Period Increase (Decrease)	2,000
Non US sovereign government supranational and government related
Concentration Risk [Line Items]
Fixed maturities, at fair value	2,180,762	3,255,154
Fixed maturities \| Non US sovereign government supranational and government related \| The World Bank
Concentration Risk [Line Items]
Fair Value, Concentration of Risk, Investments		$ 1,110,000
Fixed maturities \| Canadian goverment
Concentration Risk [Line Items]
Fair Value, Concentration of Risk, Investments	$ 776,000

Deposit contracts, allowance for credit loss

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Funds Held under Reinsurance Agreements, Allowance for Credit loss

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This item represents disclosure of all significant concentrations of credit risk or market risk arising from the subject financial instrument (as defined), whether from an individual counterparty or groups of counterparties.

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The carrying value as of the balance sheet date of the estimated valuation allowance to reduce gross premiums receivable to net realizable value.

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