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Convertible Preferred Stock and Common stock - Summary of Preferred Stock (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Shares Authorized	237,047,550	246,430,170
Shares Issued and Outstanding	221,127,100	237,047,550
Issuance Price/ Liquidation Price (Per Share)	$ 0.00001	$ 0.00001
Aggregate Liquidation Value	$ 1,422.0
Carrying Value (Net of Issuance Costs)	$ 1,419.1
Series A [Member]
Year Issued	2013
Shares Authorized	54,811,930
Shares Issued and Outstanding	54,811,930
Issuance Price/ Liquidation Price (Per Share)	$ 1.0000
Aggregate Liquidation Value	$ 54.8
Carrying Value (Net of Issuance Costs)	$ 54.7
Series B [Member]
Year Issued	2014-2015
Shares Authorized	18,133,240
Shares Issued and Outstanding	18,133,240
Issuance Price/ Liquidation Price (Per Share)	$ 2.0766
Aggregate Liquidation Value	$ 37.7
Carrying Value (Net of Issuance Costs)	$ 37.5
Series C [Member]
Year Issued	2015-2016
Shares Authorized	13,580,260
Shares Issued and Outstanding	13,580,260
Issuance Price/ Liquidation Price (Per Share)	$ 4.0500
Aggregate Liquidation Value	$ 55.0
Carrying Value (Net of Issuance Costs)	$ 54.8
Series D [Member]
Year Issued	2016-2017
Shares Authorized	15,920,450
Issuance Price/ Liquidation Price (Per Share)	$ 4.2632
Series E [Member]
Year Issued	2017-2018
Shares Authorized	78,543,890
Shares Issued and Outstanding	78,543,890
Issuance Price/ Liquidation Price (Per Share)	$ 6.7478
Aggregate Liquidation Value	$ 530.0
Carrying Value (Net of Issuance Costs)	$ 529.0
Series F [Member]
Year Issued	2018
Shares Authorized	33,686,160
Shares Issued and Outstanding	33,686,160
Issuance Price/ Liquidation Price (Per Share)	$ 11.8570
Aggregate Liquidation Value	$ 399.4
Carrying Value (Net of Issuance Costs)	$ 398.8
Series G [Member]
Year Issued	2019-2020
Shares Authorized	22,371,620
Shares Issued and Outstanding	22,371,620
Issuance Price/ Liquidation Price (Per Share)	$ 15.4269
Aggregate Liquidation Value	$ 345.1
Carrying Value (Net of Issuance Costs)	$ 344.3

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