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Basis of Presentation and Accounting Policies Revenue Recognition (Details) | 9 Months Ended
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Apr. 29, 2017
Maximum | Revenue Recognized Using Cost To Cost Percentage of Completion Method [Member] |
Revenue from External Customer [Line Items] |
Percentage of Revenue | 5.00%

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: |