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Stock-Based Compensation (Summary of the Activity for Employee Stock Unit Awards) (Details) (Employee Stock Unit Awards [Member], USD $)
In Thousands, except Per Share data, unless otherwise specified
9 Months Ended 12 Months Ended
Oct. 28, 2012
Jan. 29, 2012
Employee Stock Unit Awards [Member]
   
Number of Units    
Beginning balance 1,982  
Stock units granted 1,393  
Stock units vested (543)  
Stock units forfeited (205)  
Ending balance 2,627 1,982
Weighted Averaged Grant Date Fair Value (per unit)    
Beginning balance $ 19.06  
Stock units granted $ 26.98  
Stock units vested $ 26.35  
Stock units forfeited $ 23.47  
Ending balance $ 23.09 $ 19.06
Aggregate Intrinsic Value    
Aggregate intrinsic value of stock units vested $ 14,297 [1]  
Aggregate Unrecognized Compensation    
Beginning balance 31,472  
Ending balance $ 52,053 $ 31,472
Weighted Average Period Over Which Expected to be Recognized (in years)    
Weighted average period over which expected to be recognized (in years) 2 years 7 months 2 years 5 months
[1] Reflects the value of Semtech stock on the date that the stock unit vested.