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Organization and Description of Business (Details) - USD ($) $ / shares in Units, $ in Thousands		12 Months Ended
	Dec. 11, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2019
Subsidiary, Sale of Stock [Line Items]
Operating losses		$ 514,021	$ 384,734	$ 255,916
Accumulated deficit		$ 1,496,454	$ 1,006,627		$ 982,432
IPO
Subsidiary, Sale of Stock [Line Items]
Shares of common stock issued (in shares)	26,275,993
Price per share (usd per share)	$ 23.00
Aggregate net proceeds from the offering	$ 563,000