Stock Based Compensation (Summary Of The Activity For Restricted Share Awards) (Details) (Restricted Stock [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
Restricted Stock [Member]
Number of Shares
Beginning balance	135		418		763
Restricted stocks vested	(91)		(270)		(305)
Restricted stocks cancelled	(12)		(13)		(40)
Ending balance	32		135		418		763
Weighted Averaged Grant Date Fair Value (per share)
Beginning balance	$ 14.44		$ 15.15		$ 15.36
Restricted stocks vested	$ 14.29		$ 17.33
Restricted stocks cancelled	$ 15.25		$ 17.44
Ending balance	$ 14.57		$ 14.44		$ 15.15		$ 15.36
Aggregate Intrinsic Value
Restricted stocks vested	$ 2,201	[1]	$ 4,678	[1]	$ 4,619	[1]
Aggregate Unrecognized Compensation
Beginning balance	984		3,193		7,524
Ending balance	$ 81		$ 984		$ 3,193		$ 7,524
Period Over Which Expected to be Recognized (in years)
Beginning balance, years	0.1		0.8		1.2		2.2
Ending balance, years	0.1		0.8		1.2		2.2

[1] Represents the value of Semtech stock on the date that the restricted stock vested.