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Note 2 - Amortized Cost and Estimated Fair Value of Cash Equivalents and Marketable Securities by Maturity (Details) (USD $)
In Thousands, unless otherwise specified
May 02, 2015
Jan. 31, 2015
Book Value $ 17,699sigm_CashEquivalentsAndMarketableSecurities $ 18,104sigm_CashEquivalentsAndMarketableSecurities
Fair Value 17,839sigm_CashEquivalentsAndMarketableSecuritiesFairValueDisclosure 18,246sigm_CashEquivalentsAndMarketableSecuritiesFairValueDisclosure
Due in One Year or Less [Member]    
Book Value 8,600sigm_CashEquivalentsAndMarketableSecurities
/ sigm_ContractualMaturityAxis
= sigm_DueInOneYearOrLessMember		 13,995sigm_CashEquivalentsAndMarketableSecurities
/ sigm_ContractualMaturityAxis
= sigm_DueInOneYearOrLessMember
Fair Value 8,663sigm_CashEquivalentsAndMarketableSecuritiesFairValueDisclosure
/ sigm_ContractualMaturityAxis
= sigm_DueInOneYearOrLessMember		 13,997sigm_CashEquivalentsAndMarketableSecuritiesFairValueDisclosure
/ sigm_ContractualMaturityAxis
= sigm_DueInOneYearOrLessMember
Due in Greater Than One Year [Member]    
Book Value 9,099sigm_CashEquivalentsAndMarketableSecurities
/ sigm_ContractualMaturityAxis
= sigm_DueInGreaterThanOneYearMember		 4,109sigm_CashEquivalentsAndMarketableSecurities
/ sigm_ContractualMaturityAxis
= sigm_DueInGreaterThanOneYearMember
Fair Value $ 9,176sigm_CashEquivalentsAndMarketableSecuritiesFairValueDisclosure
/ sigm_ContractualMaturityAxis
= sigm_DueInGreaterThanOneYearMember		 $ 4,249sigm_CashEquivalentsAndMarketableSecuritiesFairValueDisclosure
/ sigm_ContractualMaturityAxis
= sigm_DueInGreaterThanOneYearMember