Fair Value Measurements - Summary of Fair Value Hierarchy for Financial Assets Measured at Fair Value on Recurring Basis (Details) - Fair value measurements recurring - Money market funds - USD ($) $ in Thousands		Oct. 31, 2017	Jan. 31, 2017
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Money market funds	[1]	$ 206,152	$ 178,245
Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Money market funds	[1]	$ 206,152	$ 178,245

[1] Included in cash and cash equivalents.