Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Unrecognized tax benefits	$ 75.6	$ 31.7	$ 27.8
Expected increase in unrecognized tax benefits	0.0
Expected decrease in unrecognized tax benefits	0.0
Domestic Tax Authority [Member]
Operating loss carryforwards	1,500.0	1,100.0
Operating loss carryforwards, not subject to expiration	2,000.0
Deferred tax assets, tax credit carryforwards, research	85.1	32.5
Domestic Tax Authority [Member] | California Franchise Tax Board [Member]
Deferred tax assets, tax credit carryforwards, research	66.0	30.9
State and Local Jurisdiction [Member]
Operating loss carryforwards	$ 3,600.0	$ 2,400.0