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Net Loss per Share - Additional Information (Details)
shares in Millions
 3 Months Ended 9 Months Ended
Oct. 31, 2018
$ / shares
shares
Oct. 31, 2018
vote
$ / shares
shares
Jul. 31, 2018
$ / shares
Class of Stock [Line Items]      
Shares issuable upon conversion (in shares) | shares 4.4 4.4  
Initial conversion price (in dollars per share) | $ / shares $ 68.15 $ 68.15 $ 68.15
Average market price (in dollars per share) | $ / shares $ 71.66    
Class A Common Stock      
Class of Stock [Line Items]      
Number of votes per share | vote   1  
Class B Common Stock      
Class of Stock [Line Items]      
Number of votes per share | vote   10