Allowance for Expected Credit Losses - Reinsurance Recoverable - Changes In Allowance for Expected Credit Losses (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
New Accounting Pronouncements or Change in Accounting Principle
Reinsurance recoverable, net	$ 1,401,681	$ 1,394,308
Reinsurance Recoverable, Allowance for Credit Loss
Balance, beginning of the period	0
Write-offs of uncollectible reinsurance	0
Write-offs of uncollectible reinsurance	0
Balance, end of the period	517
Cumulative Effect, Period of Adoption, Adjustment
Reinsurance Recoverable, Allowance for Credit Loss
Balance, beginning of the period	$ 517