Convertible Senior Notes - Schedule of Interest Expense for the Notes (Details) - Convertible Debt - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Oct. 31, 2020	Oct. 31, 2019	Oct. 31, 2020	Oct. 31, 2019
2024 Notes
Debt Instrument [Line Items]
Contractual interest expense	$ 168	$ 563	$ 506	$ 1,688
Amortization of debt discount	1,002	3,132	2,958	9,248
Amortization of issuance costs	70	202	203	585
Total	1,240	3,897	3,667	11,521
2026 Notes
Debt Instrument [Line Items]
Contractual interest expense	718	0	2,156	0
Amortization of debt discount	10,826	0	32,058	0
Amortization of issuance costs	469	0	1,366	0
Total	$ 12,013	$ 0	$ 35,580	$ 0