Document and Entity Information - USD ($)	6 Months Ended
	Jan. 27, 2018	Feb. 28, 2018	Jul. 29, 2017
Document and Entity Information [Abstract]
Entity Registrant Name	DYCOM INDUSTRIES INC
Entity Central Index Key	0000067215
Current Fiscal Year End Date	--01-27
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Public Float			$ 2,694,828,770
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	FY
Document Type	10-KT
Amendment Flag	false
Document Period End Date	Jan. 27, 2018
Entity Common Stock, Shares Outstanding		31,188,000