Accumulated Other Comprehensive Income (Loss) - Schedule of Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance, Value	$ 2,941.5	$ 1,975.4
Other comprehensive income (loss), net of tax	(15.6)	(30.0)
Ending balance, Value	2,942.4	1,855.6
Foreign Currency Translation [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance, Value	(50.8)
Other comprehensive income (loss) before reclassifications, net of tax	(15.5)
Other comprehensive income (loss), net of tax	(15.5)
Ending balance, Value	(66.3)
Unrealized Gains (Losses) on Available-For-Sale Marketable Debt Securities [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance, Value	0.1
Other comprehensive income (loss) before reclassifications, net of tax	(0.1)
Other comprehensive income (loss), net of tax	(0.1)
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance, Value	(50.7)	(125.9)
Other comprehensive income (loss) before reclassifications, net of tax	(15.6)
Other comprehensive income (loss), net of tax	(15.6)	(30.0)
Ending balance, Value	$ (66.3)	$ (155.9)