Reinsurance - 2021-2022 Reinsurance Program - Aggregate Coverage - Additional information - (Detail) $ in Millions	6 Months Ended
	Jun. 30, 2022 USD ($) Reinsurer
Reinsurance Premiums For Insurance Companies By Product Segment [Line Items]
Number of reinstatements available | Reinsurer	2
50% Aggregate Coverage [Member] | NBIC [Member]
Reinsurance Premiums For Insurance Companies By Product Segment [Line Items]
Aggregate contract expiration date	Mar. 31, 2022
Aggregate contract coverage limit	$ 20.0
Excess retention amount reinsured	21.0
Occurrence cap amount	21.0
Franchise deductible amount	$ 1.0
100.00% Aggregate Coverage [Member] | NBIC [Member]
Reinsurance Premiums For Insurance Companies By Product Segment [Line Items]
Aggregate contract expiration date	Dec. 31, 2022
Aggregate contract coverage limit	$ 20.0
Excess retention amount reinsured	$ 20.0
Number of reinstatements available | Reinsurer	1