Note 2 - Amortized Cost and Estimated Fair Value of Cash Equivalents and Marketable Securities by Maturity (Details) - USD ($) $ in Thousands	Apr. 30, 2016	Jan. 30, 2016
Due in One Year or Less [Member]
Book Value	$ 6,922	$ 4,863
Fair Value	6,949	4,893
Due in Greater Than One Year [Member]
Book Value	1,501	3,532
Fair Value	1,502	3,527
Book Value	8,423	8,395
Fair Value	$ 8,451	$ 8,420

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