Convertible Senior Notes - Schedule of Interest Expense for the Notes (Details) - Convertible Debt - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jul. 31, 2020	Jul. 31, 2019	Jul. 31, 2020	Jul. 31, 2019
2024 Notes
Debt Instrument [Line Items]
Contractual interest expense	$ 169	$ 563	$ 338	$ 1,126
Amortization of debt discount	986	3,082	1,956	6,115
Amortization of issuance costs	68	195	133	383
Total	1,223	3,840	2,427	7,624
2026 Notes
Debt Instrument [Line Items]
Contractual interest expense	719	0	1,438	0
Amortization of debt discount	10,685	0	21,231	0
Amortization of issuance costs	455	0	897	0
Total	$ 11,859	$ 0	$ 23,566	$ 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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