Stock-Based Compensation - Summary of the Activity for Employee Stock Unit Awards (Details) - Employee restricted stock unit awards [Member] - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		6 Months Ended	12 Months Ended
		Jul. 26, 2015	Jan. 25, 2015
Number of Units
Beginning balance (in shares)		2,138
Stock units granted (in shares)		370
Stock units vested (in shares)		(340)
Stock units forfeited (in shares)		(220)
Ending balance (in shares)		1,948	2,138
Weighted Averaged Grant Date Fair Value (per unit)
Beginning balance (in dollars per share)		$ 26.43
Stock units granted (in dollars per share)		27.10
Stock units vested (in dollars per share)		27.78
Stock units forfeited (in dollars per share)		26.15
Ending balance (in dollars per share)		$ 26.35	$ 26.43
Aggregate Intrinsic Value
Aggregate intrinsic value of stock units vested	[1]	$ 9,325
Aggregate Unrecognized Compensation
Beginning balance		44,506
Ending balance		$ 39,039	$ 44,506
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 5 months

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