Note 2 - Cash, Cash Equivalents and Marketable Securities - Amortized Cost and Estimated Fair Value of Cash Equivalents and Marketable Securities by Maturity (Details) - USD ($) $ in Thousands	Jan. 28, 2017	Jan. 30, 2016
Book Value	$ 8,501	$ 8,395
Fair Value	8,496	8,420
Due in One Year or Less [Member]
Book Value	8,501	4,863
Fair Value	8,496	4,893
Due in Greater Than One Year [Member]
Book Value		3,532
Fair Value		$ 3,527

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