Convertible Senior Notes, Net - Schedule of Interest Expense (Details) - Senior Notes - Convertible Senior Notes Due 2023 - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jul. 31, 2019	Jul. 31, 2018	Jul. 31, 2019	Jul. 31, 2018
Debt Instrument [Line Items]
Contractual interest expense	$ 215	$ 216	$ 431	$ 362
Amortization of debt issuance costs	329	288	648	478
Amortization of debt discount	3,759	3,554	7,465	5,935
Total	$ 4,303	$ 4,058	$ 8,544	$ 6,775

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 issuance costs.

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Amount of the cost of borrowed funds accounted for as interest expense for debt.

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