Convertible Senior Notes - Interest Expense (Details) - 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]
Total amortization of debt discount and debt issuance costs			$ 13,290	$ 7,889
Convertible Senior Notes
Debt Instrument [Line Items]
Amortization of debt discount	$ 6,341	$ 6,000	12,393	7,357
Amortization of debt issuance costs	459	434	897	532
Total amortization of debt discount and debt issuance costs	6,800	6,434	13,290	7,889
Contractual interest expense	181	181	358	224
Total interest expense related to the Notes	$ 6,981	$ 6,615	$ 13,648	$ 8,113
Effective interest rate of the liability component	5.60%	5.60%	5.60%	5.60%