Quarterly report pursuant to Section 13 or 15(d)

Redeemable Convertible Preferred Stock - Schedule of Redeemable Convertible Preferred Stock (Details)

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Redeemable Convertible Preferred Stock - Schedule of Redeemable Convertible Preferred Stock (Details) - USD ($)
$ in Thousands
4 Months Ended 9 Months Ended 12 Months Ended
Sep. 22, 2017
Sep. 30, 2018
Sep. 30, 2017
Dec. 31, 2017
Temporary Equity [Line Items]        
Issuance costs     $ (29,284)  
Accretion of issuance costs   $ 0 $ 29,259  
Series A convertible preferred stock        
Temporary Equity [Line Items]        
Series A redeemable convertible preferred stock   480,000   $ 480,000
Issuance costs $ (29,300) (29,318)   (29,318)
Accretion of issuance costs   29,318   29,318
Stock dividend payable to preferred stockholders   33,270   10,849
Redeemable convertible preferred stock   $ 513,270   $ 490,849