Interest Expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Apr. 30, 2019	Apr. 30, 2018
Debt Instrument [Line Items]
Total amortization of debt discount and debt issuance costs	$ 6,490	$ 1,455
Convertible Senior Notes
Debt Instrument [Line Items]
Amortization of debt discount	6,052	1,357
Amortization of debt issuance costs	438	98
Total amortization of debt discount and debt issuance costs	6,490	1,455
Contractual interest expense	177	43
Total interest expense related to the Notes	$ 6,667	$ 1,498
Effective interest rate of the liability component	5.60%	5.60%