Income Taxes - Reconciliation of Difference Between Provision for Income Taxes and Expected Tax Provision at Weighted Average Tax Rate (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Income tax provision (benefit) at expected rate	$ (14.7)	$ 9.8	$ 4.0
Tax effect of:
Nontaxable investment income	(0.4)	(0.5)	(0.7)
Foreign exchange adjustments	(2.1)	(0.7)	1.6
Impairment of goodwill	5.4	8.2	1.0
Withholding taxes	2.7	0.1	0.1
Change in uncertain tax position liability	(1.4)	(4.5)	0.7
Change in valuation allowance	(7.6)	(0.7)	0.5
Impact of change in tax rate related to Finance Act 2021	1.7	(8.3)	0.0
Brazil Premiums and Underwriting	0.3	(5.3)	0.0
Sale of Brazil and Malta Operations	6.6	0.0	0.0
Other	1.5	0.5	0.5
Income tax provision (benefit)	$ (8.0)	$ (1.4)	$ 7.7