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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
12 Months Ended
Jan. 29, 2012
years
Jan. 30, 2011
years
Jan. 31, 2010
years
Jan. 25, 2009
years
Employee Stock Unit Awards [Member]
       
Number of Units        
Beginning balance 2,058 1,410 316  
Stock units granted 810 1,181 1,205  
Stock units vested (627) (404) (66)  
Stock units forfeited (259) (129) (45)  
Ending balance 1,982 2,058 1,410 316
Weighted Averaged Grant Date Fair Value (per unit)        
Beginning balance $ 16.70 $ 15.72 $ 14.97  
Stock units granted $ 22.74 $ 17.62 $ 15.84  
Stock units vested $ 16.61 $ 19.20    
Stock units forfeited $ 17.75 $ 19.50    
Ending balance $ 19.06 $ 16.70 $ 15.72 $ 14.97
Aggregate Intrinsic Value        
Vested, Aggregate intrinsic value $ 14,333 [1] $ 7,749 [1] $ 1,137 [1]  
Aggregate Unrecognized Compensation        
Beginning balance 29,763 17,713 3,345  
Ending balance $ 31,472 $ 29,763 $ 17,713 $ 3,345
Period Over Which Expected to be Recognized (in years)        
Beginning balance, years 2.4 2.7 3.4 3.6
Ending balance, years 2.4 2.7 3.4 3.6
[1] Reflects the value of Semtech stock on the date that the stock unit vested.