Cash Equivalents and Short-Term Investments - Schedule of Contractual Maturities of Short-term Investments (Details) - USD ($) $ in Thousands	Oct. 31, 2018	Jan. 31, 2018
Amortized Cost
Amortized cost, due within one year	$ 350,351	$ 93,421
Amortized cost, due between one to five years	0	8,546
Amortized Cost	350,351	101,967
Estimated Fair Value
Estimated fair value, due within one year	350,105	93,237
Estimated fair value, due between one to five years	0	8,528
Estimated fair value, total	$ 350,105	$ 101,765

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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