Face (par) amount of debt instrument at time of issuance.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28551-108399

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=114775985&loc=d3e28878-108400

Name:	us-gaap_DebtInstrumentFaceAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Commitments and Contingencies - Narrative (Details) - USD ($)	Oct. 31, 2019	Jan. 31, 2019	Apr. 30, 2018
Lessee, Lease, Description [Line Items]
Outstanding letters of credit	$ 11,500,000	$ 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