Securities Available for Sale - Additional Information (Detail)	9 Months Ended
Oct. 28, 2017 USD ($)
Schedule of Available-for-sale Securities [Line Items]
Impairment charges on available for sale security	$ 0
Minimum [Member]
Schedule of Available-for-sale Securities [Line Items]
Original maturity of short-term investments	90 days
Anticipated maturity period	1 month
Maximum [Member]
Schedule of Available-for-sale Securities [Line Items]
Anticipated maturity period	16 months

The amount by which the fair value of an investment in debt and equity securities categorized as Available-for-sale is less than the amortized cost basis or carrying amount of that investment at the balance sheet date and the decline in fair value is deemed to be other than temporary, before considering whether or not such amount is recognized in earnings or other comprehensive income.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 8A
-URI http://asc.fasb.org/extlink&oid=82896770&loc=SL6284422-111562

Name:	us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsAvailableforsaleSecurities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration