Accumulated Other Comprehensive Income (Loss) - Changes in Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	$ 1,857.8	$ 1,763.7
Other comprehensive (loss) income before reclassifications	(73.3)	62.9
Amounts reclassified from accumulated other comprehensive income	(8.0)	(12.8)
Net current-period other comprehensive income (loss)	(81.3)	50.1
Ending Balance	1,735.2	1,857.8
Cumulative Effect, Period of Adoption, Adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance		(2.2)
Foreign Currency Translation Adjustments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(37.9)	(22.6)
Other comprehensive (loss) income before reclassifications	2.6	(15.3)
Amounts reclassified from accumulated other comprehensive income	0.0	0.0
Net current-period other comprehensive income (loss)	2.6	(15.3)
Ending Balance	(35.3)	(37.9)
Foreign Currency Translation Adjustments | Cumulative Effect, Period of Adoption, Adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance		0.0
Unrealized Holding Gains on Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	105.1	33.5
Other comprehensive (loss) income before reclassifications	(77.4)	78.7
Amounts reclassified from accumulated other comprehensive income	(8.0)	(12.8)
Net current-period other comprehensive income (loss)	(85.4)	65.9
Ending Balance	19.7	105.1
Unrealized Holding Gains on Securities | Cumulative Effect, Period of Adoption, Adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance		5.7
Defined Benefit Pension Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(8.6)	(8.1)
Other comprehensive (loss) income before reclassifications	1.5	(0.5)
Amounts reclassified from accumulated other comprehensive income	0.0	0.0
Net current-period other comprehensive income (loss)	1.5	(0.5)
Ending Balance	(7.1)	(8.6)
Defined Benefit Pension Plans | Cumulative Effect, Period of Adoption, Adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance		0.0
AOCI Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	58.6	2.8
Ending Balance	$ (22.7)	58.6
AOCI Attributable to Parent | Cumulative Effect, Period of Adoption, Adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance		$ 5.7