Summary of Significant Accounting Policies - Allowance for Credit Losses on Reinsurance Recoverables (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Beginning balance	$ 0	$ 0	$ 0
Provision during the period for expected credit losses	(68)	0	0
Write-off amounts during the period	0	0	0
Recoveries during the period of amounts previously written off	0	0	0
Ending balance	91	0	0
Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Beginning balance	159	0	0
Ending balance		159	0
Cumulative Effect, Period of Adoption, Adjusted Balance
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Beginning balance	$ 159	0	0
Ending balance		$ 159	$ 0