Convertible Senior Notes - Schedule of Interest Expense for the Notes (Details) - Convertible Debt - USD ($) $ in Thousands	3 Months Ended
Apr. 30, 2020	Apr. 30, 2019
2024 Notes
Debt Instrument [Line Items]
Contractual interest expense	$ 169	$ 563
Amortization of debt discount	970	3,033
Amortization of issuance costs	65	188
Total	1,204	3,784
2026 Notes
Debt Instrument [Line Items]
Contractual interest expense	719	0
Amortization of debt discount	10,547	0
Amortization of issuance costs	441	0
Total	$ 11,707	$ 0

Amount of noncash expense included in interest expense to amortize debt discount and premium associated with the related debt instruments. Excludes amortization of financing costs. Alternate captions include noncash interest expense.

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