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Stock-Based Compensation (Summary Of The Activity For Employees Stock Unit Awards) (Details) (Employee Stock Unit Awards [Member], USD $)
In Thousands, except Per Share data, unless otherwise specified
9 Months Ended
Oct. 30, 2011
Employee Stock Unit Awards [Member]
 
Number of Units  
Beginning balance 2,058
Stock units granted 692
Stock units vested (452)
Stock units forfeited (245)
Ending balance 2,053
Weighted Averaged Grant Date Fair Value (per unit)  
Beginning balance $ 16.70
Stock units granted $ 22.56
Stock units vested $ 16.30
Stock units forfeited $ 17.68
Ending balance $ 18.64
Aggregate Intrinsic Value  
Stock units vested $ 10,280 [1]
Aggregate Unrecognized Compensation  
Beginning balance 29,763
Ending balance $ 32,158
Weighted Average Period Over Which Expected to be Recognized (in years)  
Beginning balance 2.7
Ending balance 2.5
[1] Reflects the value of Semtech stock on the date that the stock unit vested.