Allowance for Expected Credit Losses - Premiums Receivable and Reinsurance Receivables - Schedule of Allowance for Credit Losses Related to Reinsurance Receivables (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Reinsurance Receivables
Beginning balance	$ 8,992	$ 8,992
Current period provision for expected credit losses	(71)	0
Write-offs	0	0
Recoveries of amounts previously written off	71	0
Ending balance	$ 8,992	$ 8,992