Income Taxes - Losses Before Provision for Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
United States	$ (340,301)	$ (306,758)	$ (291,049)
Foreign	206	153	85
Loss before provision for income taxes	$ (340,095)	$ (306,605)	$ (290,964)