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Cash Equivalents and Short-Term Investments - Schedule of Amortized Costs, Unrealized Gains and Losses and Estimated Fair Value of Cash Equivalents and Short-term Investments (Details) - USD ($)
$ in Thousands
Jul. 31, 2017
Jan. 31, 2017
Cash equivalents:    
Cash equivalents, amortized cost $ 115,511 $ 10,565
Cash equivalents, estimated fair value 115,511 10,565
Investments:    
Investments, amortized cost 86,767 14,380
Investments, estimated fair value 86,755 14,390
Total short-term investments, amortized cost 86,767 14,380
Total short-term investments, unrealized gain 2 13
Total short-term investments, unrealized loss (14) (3)
Total short-term investments, estimated fair value 86,755 14,390
Amortized cost 202,278 24,945
Estimated fair value 202,266 24,955
Commercial paper    
Investments:    
Investments, amortized cost 18,913  
Investments, unrealized gain 0  
Investments, unrealized loss 0  
Investments, estimated fair value 18,913  
U.S. treasury securities    
Investments:    
Investments, amortized cost 45,083  
Investments, unrealized gain 1  
Investments, unrealized loss (3)  
Investments, estimated fair value 45,081  
Corporate debt securities    
Investments:    
Investments, amortized cost 22,771 12,842
Investments, unrealized gain 1 13
Investments, unrealized loss (11) (3)
Investments, estimated fair value 22,761 12,852
Asset-backed securities    
Investments:    
Investments, amortized cost   1,538
Investments, unrealized gain   0
Investments, unrealized loss   0
Investments, estimated fair value   $ 1,538
Money market funds    
Cash equivalents:    
Cash equivalents, amortized cost 95,495  
Cash equivalents, estimated fair value 95,495  
Commercial paper    
Cash equivalents:    
Cash equivalents, amortized cost 15,020  
Cash equivalents, estimated fair value 15,020  
U.S. treasury securities    
Cash equivalents:    
Cash equivalents, amortized cost 4,996  
Cash equivalents, estimated fair value $ 4,996