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Selected Quarterly Financial Data (Unaudited) - Narrative (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Jan. 28, 2018 | Jan. 29, 2017 | Jan. 31, 2016
Selected Quarterly Financial Information [Abstract] |  |  |
Loss (gain) on disposition of business operations and assets | $ (276) | $ 25,489 | $ (23)

X
- Definition Gain (Loss) on Disposition of Business and Property Plant and Equipment + References No definition available. + Details
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Namespace Prefix: | smtc_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- References No definition available. + Details
Name: | us-gaap_SelectedQuarterlyFinancialInformationAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration