Stock-Based Awards - Tax Benefit Recognized (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
Jan. 27, 2018	Jul. 29, 2017	Jul. 30, 2016	Jul. 25, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock-based compensation	$ 13,277	$ 20,805	$ 16,850	$ 13,923
Income tax effect of stock-based compensation	4,793	$ 7,996	$ 6,436	$ 5,458
Cash tax benefit realized from option exercises and stock vestings	$ 7,800

Effective Income Tax Rate Reconciliation, Share-based Compensation, Excess Tax Benefit, Amount

No definition available.

Name:	dy_EffectiveIncomeTaxRateReconciliationSharebasedCompensationExcessTaxBenefitAmount
Namespace Prefix:	dy_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- References

No definition available.

+ Details

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

- Definition

The total recognized tax benefit related to compensation cost for equity-based payment arrangements recognized in income during the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (h)(1)(i)
-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

+ Details

Name:	us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The aggregate amount of noncash, equity-based employee remuneration. This may include the value of stock or unit options, amortization of restricted stock or units, and adjustment for officers' compensation. As noncash, this element is an add back when calculating net cash generated by operating activities using the indirect method.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3602-108585

+ Details

Name:	us-gaap_ShareBasedCompensation
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration