Convertible Senior Notes - Schedule of Interest Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Oct. 31, 2020	Oct. 31, 2019	Oct. 31, 2020	Oct. 31, 2019
Debt Instrument
Amortization of debt discount and issuance costs			$ 71,655	$ 59,477
Convertible Senior Notes | 2023 Notes
Debt Instrument
Coupon interest expense	$ 971	$ 1,581	3,726	4,743
Amortization of debt discount (conversion option)	8,040	12,390	30,062	36,203
Amortization of debt discount and issuance costs	315	484	1,174	1,414
Total interest expense	9,326	14,455	34,962	42,360
Convertible Senior Notes | 2025 Notes
Debt Instrument
Coupon interest expense	2,426	2,426	7,278	7,278
Amortization of debt discount (conversion option)	7,767	7,308	22,728	21,276
Amortization of debt discount and issuance costs	213	201	624	585
Total interest expense	10,406	9,935	30,630	29,139
Convertible Senior Notes | 2027 Notes
Debt Instrument
Coupon interest expense	3,558	0	5,732	0
Amortization of debt discount (conversion option)	10,168	0	16,398	0
Amortization of debt discount and issuance costs	414	0	668	0
Total interest expense	$ 14,140	$ 0	$ 22,798	$ 0