Allowance for Expected Credit Losses - Premiums Receivable and Reinsurance Receivables - Schedule of Allowance for Credit Losses Related to Premiums Receivable (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Premiums Receivable
Beginning balance	$ 2,900	$ 2,754
Current period provision for expected credit losses	88	162
Write-offs	(216)	(170)
Ending balance	$ 2,772	$ 2,746