Convertible Senior Notes - Schedule of Interest Expense (Details) - USD ($) $ in Thousands	3 Months Ended
Apr. 30, 2020	Apr. 30, 2019
Debt Instrument
Amortization of debt issuance costs and purchase discounts	$ (20,416)	$ (19,005)
Convertible Senior Notes \| 2023 Notes
Debt Instrument
Coupon interest expense	1,581	1,581
Amortization of debt discount (conversion option)	12,418	11,595
Amortization of debt issuance costs and purchase discounts	485	453
Total interest expense	14,484	13,629
Convertible Senior Notes \| 2025 Notes
Debt Instrument
Coupon interest expense	2,426	2,426
Amortization of debt discount (conversion option)	7,312	6,771
Amortization of debt issuance costs and purchase discounts	201	186
Total interest expense	$ 9,939	$ 9,383

Convertible Debt, Coupon Interest Expense

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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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Amount of amortization expense attributable to debt discount (premium) and debt issuance costs.

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The after-tax amount of interest recognized in the period associated with any convertible debt.

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