Convertible Senior Notes - Interest Expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Apr. 30, 2018	Apr. 30, 2017	[1]
Debt Instrument [Line Items]
Total amortization of debt discount and debt issuance costs	$ 1,455	$ 0
Convertible Senior Notes
Debt Instrument [Line Items]
Amortization of debt discount	1,357
Amortization of debt issuance costs	98
Total amortization of debt discount and debt issuance costs	1,455
Contractual interest expense	43
Total interest expense related to the Notes	$ 1,498
Effective interest rate of the liability component	5.60%

[1] * Prior period information has been adjusted to reflect the adoption impact of ASC 606 and ASU 2016-18, which we adopted on February 1, 2018