Income Taxes - Valuation Allowance (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Valuation Allowance [Line Items]
Valuation allowance	$ 94.3	$ 85.6
Change in valuation allowance	19.6	2.0	$ 26.6
Income tax expense (benefit)	41.4	44.4	$ (14.8)
U.S. losses and other federal deferred tax benefits
Valuation Allowance [Line Items]
Valuation allowance	56.6	38.2
Net operating losses in Israel subsidiaries
Valuation Allowance [Line Items]
Valuation allowance	20.4	21.9
Luxembourg | U.S. losses and other federal deferred tax benefits
Valuation Allowance [Line Items]
Change in valuation allowance	9.2	1.6
United Kingdom | Net operating losses in United Kingdom subsidiaries
Valuation Allowance [Line Items]
Change in valuation allowance	1.0	3.1
United States | Net operating losses in US branches
Valuation Allowance [Line Items]
Income tax expense (benefit)		0.6
Israel | Net operating losses in Israel subsidiaries
Valuation Allowance [Line Items]
Change in valuation allowance	1.5	1.9
Subsidiaries | Luxembourg | Net operating losses in Luxembourg subsidiaries
Valuation Allowance [Line Items]
Valuation allowance	16.0	25.2
Subsidiaries | United Kingdom | Net operating losses in Luxembourg subsidiaries
Valuation Allowance [Line Items]
Valuation allowance	1.3	0.3
Guilford Holdings, Inc. | United States
Valuation Allowance [Line Items]
Change in valuation allowance	7.8
Income tax expense (benefit)		(3.6)
BAM | United States
Valuation Allowance [Line Items]
Income tax expense (benefit)	17.5	7.8
BAM | United States | MSC
Valuation Allowance [Line Items]
Income tax expense (benefit)	(10.9)	$ (7.5)
BAM | United States | Foreign Tax Credits
Valuation Allowance [Line Items]
Income tax expense (benefit)	$ 4.0