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	Feb. 03, 2018	Jan. 28, 2017
Book Value		$ 8,501
Fair Value		8,496
Due in One Year or Less [Member]
Book Value		8,501
Fair Value		8,496
Due in Greater Than One Year [Member]
Book Value
Fair Value

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