Commitments and Contingencies - Narrative (Details) - USD ($)	Jul. 31, 2019	Jan. 31, 2019	Jul. 31, 2018	Apr. 30, 2018
Lessee, Lease, Description [Line Items]
Outstanding letters of credit	$ 11,600,000	$ 10,800,000
Letter of Credit
Lessee, Lease, Description [Line Items]
Principal amount		$ 500,000
Convertible Senior Notes
Lessee, Lease, Description [Line Items]
Principal amount			$ 575,000,000.0	$ 575,000,000.0