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Basis of Presentation and Accounting Policies - Revenue Recognition (Details)	12 Months Ended
	Jul. 29, 2017	Jul. 30, 2016
Maximum | Revenue Recognized Using Cost To Cost Percentage of Completion Method
Revenue from External Customer [Line Items]
Percentage of Revenue	5.00%	10.00%

X

- Definition

Amount considered as a portion of total revenue for the fiscal period.

+ References

No definition available.

+ Details

Name:	dy_PercentageofRevenue
Namespace Prefix:	dy_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_EntityWideInformationRevenueFromExternalCustomerLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Details

Name:	us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ProductOrServiceAxis=dy_RevenueRecognizedUsingCostToCostPercentageofCompletionMethodMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: