Cash Equivalents and Short-term Investments - Schedule of Contractual Maturities of Short-term Investments (Details) - USD ($) $ in Thousands	Jan. 31, 2018	Jan. 31, 2017
Amortized Cost
Amortized cost, due within one year	$ 93,421	$ 12,842
Amortized cost, due between one to five years	8,546	1,538
Investments, amortized cost	101,967	14,380
Estimated Fair Value
Estimated fair value, due within one year	93,237	12,852
Estimated fair value, due between one to five years	8,528	1,538
Estimated fair value total	$ 101,765	$ 14,390