Convertible Senior Notes - Interest Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Oct. 31, 2019	Oct. 31, 2018	Oct. 31, 2019	Oct. 31, 2018
Debt Instrument [Line Items]
Total amortization of debt discount and debt issuance costs			$ 20,186	$ 14,414
Convertible Senior Notes
Debt Instrument [Line Items]
Amortization of debt discount	$ 6,431	$ 6,084	18,824	13,441
Amortization of debt issuance costs	465	441	1,362	973
Total amortization of debt discount and debt issuance costs	6,896	6,525	20,186	14,414
Contractual interest expense	181	181	539	405
Total interest expense related to the Notes	$ 7,077	$ 6,706	$ 20,725	$ 14,819
Effective interest rate of the liability component	5.60%	5.60%	5.60%	5.60%