v3.20.1
Stock-Based Compensation - Stock Option Activity (Details) - Options - $ / shares
 12 Months Ended
Jan. 31, 2020
Jan. 31, 2019
Jan. 31, 2018
Number of Shares      
Options outstanding, beginning balance (in shares) 26,535,000 23,194,000 19,347,000
Options granted (in shares) 1,048,000 8,233,000 9,691,000
Options exercised (in shares) (11,682,000) (3,084,000) (3,733,000)
Options canceled (in shares) (1,212,000) (1,808,000) (2,111,000)
Options outstanding, ending balance (in shares) 14,689,000 26,535,000 23,194,000
Options, vested and expected to vest (in shares) 14,689,000    
Options exercisable (in shares) 7,288,000    
Weighted- Average Exercise Price Per Share      
Options outstanding, beginning balance, weighted average exercise price (in usd per share) $ 3.87 $ 1.51 $ 1.10
Options granted, weighted average exercise price (in usd per share) 17.76 9.24 2.14
Options exercised, weighted average exercise price (in usd per share) 2.72 1.26 1.00
Options canceled, weighted average exercise price per share (in usd per share) 6.91 2.51 1.57
Options outstanding, ending balance, weighted average exercise price (in usd per share) 5.52 $ 3.87 $ 1.51
Options vested and expected to vest, weighted average exercise price (in usd per share) 5.52    
Options exercisable, weighted average exercise price (in usd per share) $ 3.15