Cash Equivalents and Short-Term Investments - Schedule of Contractual Maturities of Short-term Investments (Details) - USD ($) $ in Thousands	Oct. 31, 2017	Jan. 31, 2017
Amortized Cost
Amortized cost, due within one year	$ 73,602	$ 12,842
Amortized cost, due between one to five years	12,511	1,538
Investments, amortized cost	86,113	14,380
Estimated Fair Value
Estimated fair value, due within one year	73,553	12,852
Estimated fair value, due between one to five years	12,490	1,538
Estimated fair value total	$ 86,043	$ 14,390