Commitments and Contingencies - Additional Information (Detail) $ in Millions	Sep. 30, 2020 USD ($)
June 1, 2020 - May 31, 2021 [Member]
Reinsurance Retention Policy [Line Items]
Reinsurance payable, next twelve months	$ 128.3
June 1, 2019 - May 31, 2020 [Member]
Reinsurance Retention Policy [Line Items]
Reinsurance payable, due in second year	$ 71.3

Amount of commitment classified as other to be paid in next fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

No definition available.

Name:	us-gaap_OtherCommitmentDueInNextTwelveMonths
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant