Short-Term Investments - Summary of Estimated Fair Value of Short-Term Investments, Designated as Available-for-Sale and Classified by Contractual Maturity (Detail) - USD ($) $ in Thousands	Jul. 31, 2018	Jan. 31, 2018
Investments Debt And Equity Securities [Abstract]
Due in one year or less	$ 331,500	$ 308,172
Due in greater than one year	167,190	133,607
Total	$ 498,690	$ 441,779	[1]

[1] See note 1 of the notes to the condensed consolidated financial statements for a summary of adjustments.