Investments - Summary Of Unrealized Gains (Losses) On Investments (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jul. 31, 2016	Jul. 26, 2015	Jul. 31, 2016	Jul. 26, 2015
Investments [Abstract]
Unrealized gain (loss), net of tax	$ 0	$ 84	$ (85)	$ 138
Increase to deferred tax liability	$ 0	$ 56	$ 0	$ 98

The change in unrealized holding gain (loss), net of tax, on available-for-sale securities included in a separate component of shareholders' equity during the period.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 9
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27357-111563

Name:	us-gaap_AvailableForSaleSecuritiesChangeInNetUnrealizedHoldingGainLossNetOfTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration