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. 25, 2015		Jan. 26, 2014		Jan. 27, 2013		Jan. 29, 2012
Employee stock unit awards
Number of Units
Beginning balance (in shares)	2,195		2,558		1,982
Stock units granted (in shares)	929		891		1,517
Stock units vested (in shares)	(752)		(1,026)		(699)
Stock units forfeited (in shares)	(234)		(228)		(242)
Ending balance (in shares)	2,138		2,195		2,558		1,982
Weighted Averaged Grant Date Fair Value (per unit)
Beginning balance (in dollars per share)	$ 27.18		$ 23.41		$ 19.06
Weighted average fair value units granted (in dollars per share)	$ 23.90		$ 30.95		$ 26.73
Stock units vested (in dollars per share)	$ 25.55		$ 21.34		$ 18.20
Stock units forfeited (in dollars per share)	$ 26.29		$ 25.81		$ 23.65
Ending balance (in dollars per share)	$ 26.43		$ 27.18		$ 23.41		$ 19.06
Aggregate Intrinsic Value
Aggregate intrinsic value of stock units vested	$ 18,237	[1]	$ 31,861	[1]	$ 18,438	[1]
Aggregate Unrecognized Compensation
Beginning balance	49,563		49,374		31,472
Ending balance	$ 44,506		$ 49,563		$ 49,374		$ 31,472
Weighted Average Remaining Expense Period (in years)
Ending Balance	2 years 5 months		2 years 6 months		2 years 6 months		2 years 5 months

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