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	6 Months Ended		12 Months Ended
	Jul. 28, 2013		Jan. 27, 2013
Employee stock unit awards [Member]
Number of Units
Beginning balance (in shares)	2,558
Stock units granted (in shares)	308
Stock units vested (in shares)	(504)
Stock units forfeited (in shares)	(97)
Ending balance (in shares)	2,265		2,558
Weighted Averaged Grant Date Fair Value (per unit)
Beginning balance (in dollars per share)	$ 23.41
Stock units granted (in dollars per share)	$ 32.50
Stock units vested (in dollars per share)	$ 22.59
Stock units forfeited (in dollars per share)	$ 24.60
Ending balance (in dollars per share)	$ 24.78		$ 23.41
Aggregate Intrinsic Value
Aggregate intrinsic value of stock units vested	$ 16,317	[1]
Aggregate Unrecognized Compensation
Beginning balance	49,374
Ending balance	$ 45,996		$ 49,374
Weighted Average Period Over Which Expected to be Recognized (in years)
Weighted average period over which expected to be recognized	2 years 4 months		2 years 6 months

[1] Reflects the value of Semtech stock on the date that the stock unit vested.