Selected Quarterly Financial Data (Unaudited) - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
Jan. 27, 2019	Jan. 28, 2018	Jan. 29, 2017
Selected Quarterly Financial Information [Abstract]
Loss (gain) on disposition of business operations and assets	$ 26	$ (276)	$ 25,489

Gain (Loss) on Disposition of Business and Property Plant and Equipment

No definition available.

Name:	smtc_GainLossonDispositionofBusinessandPropertyPlantandEquipment
Namespace Prefix:	smtc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration