Losses and Loss Adjustment Expenses - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Reserves For Losses And Loss Adjustment Expenses [Line Items]
Unpaid claims and claim adjustment expenses overall development	$ 27,637	$ 1,800	$ 10,559
Unpaid claims and claim adjustment expenses overall development	199,888	$ 158,236	$ 96,955
Accidental Year 2020 [Member] | Hurricane Sally and Tropical Storm Eta [Member]
Reserves For Losses And Loss Adjustment Expenses [Line Items]
Unpaid claims and claim adjustment expenses overall development	27,637
Accident Year 2021 [Member] | United [Member]
Reserves For Losses And Loss Adjustment Expenses [Line Items]
Unpaid claims and claim adjustment expenses overall development	45,578
Accident Year 2021 [Member] | United [Member] | Typ Tap [Member]
Reserves For Losses And Loss Adjustment Expenses [Line Items]
Unpaid claims and claim adjustment expenses overall development	$ 14,135