Convertible Senior Notes - Interest Expense (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Oct. 31, 2018	Oct. 31, 2018	Oct. 31, 2017	[1]
Debt Instrument [Line Items]
Total amortization of debt discount and debt issuance costs		$ 14,414	$ 0
Convertible Senior Notes
Debt Instrument [Line Items]
Amortization of debt discount	$ 6,084	13,441
Amortization of debt issuance costs	441	973
Total amortization of debt discount and debt issuance costs	6,525	14,414
Contractual interest expense	181	405
Total interest expense related to the Notes	$ 6,706	$ 14,819
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 Accounting Standards Update No. 2016-18, Statement of Cash Flows (Topic 230): Restricted Cash (ASU 2016-18), which we adopted on February 1, 2018