Convertible Senior Notes - Schedule of Interest Expense for the Notes (Details) - Convertible Debt - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 31, 2018	Jul. 31, 2017	Jul. 31, 2018	Jul. 31, 2017
Debt Instrument [Line Items]
Contractual interest expense	$ 200	$ 0	$ 200	$ 0
Amortization of debt discount	1,034	0	1,034	0
Amortization of issuance costs	60	0	60	0
Total	$ 1,294	$ 0	$ 1,294	$ 0