Debt - Schedule of Interest Expense Recognized Related to Notes (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Debt Disclosure [Abstract]
Contractual interest expense	$ 0.4	$ 0.4	$ 1.3	$ 1.3
Amortization of debt discount	12.3	5.6	36.4	16.7
Amortization of transaction costs	1.2	0.7	3.8	2.1
Total	$ 13.9	$ 6.7	$ 41.5	$ 20.1