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. 31, 2016	Jan. 31, 2016
Number of Units
Beginning balance (in shares)		2,032
Stock units granted (in shares)		629
Stock units vested (in shares)		(360)
Stock units forfeited (in shares)		(128)
Ending balance (in shares)		2,173	2,032
Weighted Averaged Grant Date Fair Value (per unit)
Beginning balance		$ 23.70
Stock units granted		18.38
Stock units vested (in dollars per share)		27.82
Stock units forfeited (in dollars per share)		20.56
Ending balance		$ 21.67	$ 23.70
Aggregate Intrinsic Value
Aggregate intrinsic value of stock units vested	[1]	$ 7,152
Aggregate Unrecognized Compensation
Beginning balance		35,692
Ending balance		$ 35,623	$ 35,692
Weighted Average Period Over Which Expected to be Recognized (in years)
Weighted average period over which expected to be recognized		2 years 5 months	2 years 5 months

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