Fair Value Measurements - Additional Information (Detail)	Jan. 31, 2019 USD ($)
Fair Value Measurements Disclosure [Line Items]
Marketable securities fair value, mature between one and three years	$ 6,300,000
Fair Value, Inputs, Level 3 [Member]
Fair Value Measurements Disclosure [Line Items]
Fair value measurements of our financial assets	$ 0

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19207-110258

Name:	us-gaap_AssetsFairValueDisclosure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant