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Stock-Based Compensation - Summary of the Activity for Employee Stock Unit Awards (Details) (Employee stock unit awards, USD $)
In Thousands, except Per Share data, unless otherwise specified
12 Months Ended
Jan. 26, 2014
Jan. 27, 2013
Jan. 29, 2012
Jan. 30, 2011
Employee stock unit awards
       
Number of Units        
Beginning balance (in shares) 2,558 1,982 2,058  
Stock units granted (in shares) 891 1,517 810  
Stock units vested (in shares) (1,026) (699) (627)  
Stock units forfeited (in shares) (228) (242) (259)  
Ending balance (in shares) 2,195 2,558 1,982 2,058
Weighted Averaged Grant Date Fair Value (per unit)        
Beginning balance (in dollars per share) $ 23.41 $ 19.06 $ 16.70  
Stock units granted (in dollars per share) $ 30.95 $ 26.73 $ 22.74  
Stock units vested (in dollars per share) $ 21.34 $ 18.20 $ 16.61  
Stock units forfeited (in dollars per share) $ 25.81 $ 23.65 $ 17.75  
Ending balance (in dollars per share) $ 27.18 $ 23.41 $ 19.06 $ 16.70
Aggregate Intrinsic Value        
Aggregate intrinsic value of stock units vested $ 31,861 [1] $ 18,438 [1] $ 14,333 [1]  
Aggregate Unrecognized Compensation        
Beginning balance 49,374 31,472 29,763  
Ending balance $ 49,563 $ 49,374 $ 31,472 $ 29,763
Weighted Average Period Over Which Expected to be Recognized (in years)        
Ending Balance 2 years 6 months 2 years 6 months 2 years 5 months 2 years 8 months
[1] Reflects the value of Semtech stock on the date that the stock unit vested.