Note 2 - Amortized Cost and Estimated Fair Value of Cash Equivalents and Marketable Securities by Maturity (Details) - USD ($) $ in Thousands	Aug. 01, 2015	Jan. 31, 2015
Due in One Year or Less [Member]
Book Value	$ 12,150	$ 13,995
Fair Value	12,189	13,997
Due in Greater Than One Year [Member]
Book Value	5,540	4,109
Fair Value	5,591	4,249
Book Value	17,690	18,104
Fair Value	$ 17,780	$ 18,246

Amount of (1) short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates; and (2) debt and equity financial instruments including: (i) securities held-to-maturity, (ii) trading securities, and (iii) securities available-for-sale.

No definition available.

Name:	sigm_CashEquivalentsAndMarketableSecurities
Namespace Prefix:	sigm_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant