Convertible Senior Notes - Interest Expense (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jul. 31, 2018	Jul. 31, 2018	Jul. 31, 2017	[1]
Debt Instrument [Line Items]
Total amortization of debt discount and debt issuance costs		$ 7,889	$ 0
Convertible Senior Notes
Debt Instrument [Line Items]
Amortization of debt discount	$ 6,000	7,357
Amortization of debt issuance costs	434	532
Total amortization of debt discount and debt issuance costs	6,434	7,889
Contractual interest expense	181	224
Total interest expense related to the Notes	$ 6,615	$ 8,113
Effective interest rate of the liability component	5.60%	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