Supplemental Consolidating Financial Statements - Income Statement (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	6 Months Ended
Jan. 24, 2015	Jan. 25, 2014	Jan. 24, 2015	Jan. 25, 2014
Revenues [Abstract]
Contract revenues	$ 441,081us-gaap_SalesRevenueServicesNet	$ 390,518us-gaap_SalesRevenueServicesNet	$ 951,470us-gaap_SalesRevenueServicesNet	$ 903,238us-gaap_SalesRevenueServicesNet
EXPENSES:
Costs of earned revenues, excluding depreciation and amortization	355,429	327,353	758,898	737,472
General and administrative	41,815us-gaap_GeneralAndAdministrativeExpense	38,562us-gaap_GeneralAndAdministrativeExpense	86,511us-gaap_GeneralAndAdministrativeExpense	81,637us-gaap_GeneralAndAdministrativeExpense
Depreciation and amortization	23,264	23,435	46,193	46,987
Intercompany charges (income), net	0dy_IntercompanyChargesIncome	0dy_IntercompanyChargesIncome	0dy_IntercompanyChargesIncome	0dy_IntercompanyChargesIncome
Interest expense, net	(6,730)us-gaap_InterestIncomeExpenseNet	(6,800)us-gaap_InterestIncomeExpenseNet	(13,480)us-gaap_InterestIncomeExpenseNet	(13,686)us-gaap_InterestIncomeExpenseNet
Other income, net	1,735us-gaap_OtherNonoperatingIncomeExpense	595us-gaap_OtherNonoperatingIncomeExpense	3,530us-gaap_OtherNonoperatingIncomeExpense	2,607us-gaap_OtherNonoperatingIncomeExpense
Income (loss) before income taxes	15,578	(5,037)	49,918	26,063
Provision (benefit) for income taxes:	6,146us-gaap_IncomeTaxExpenseBenefit	(1,970)us-gaap_IncomeTaxExpenseBenefit	19,679us-gaap_IncomeTaxExpenseBenefit	10,470us-gaap_IncomeTaxExpenseBenefit
Net income (loss) before equity in earnings of subsidiaries	9,432	(3,067)	30,239	15,593
Equity in earnings of subsidiaries	0dy_EquityInEarningsOfSubsidiaries	0dy_EquityInEarningsOfSubsidiaries	0dy_EquityInEarningsOfSubsidiaries	0dy_EquityInEarningsOfSubsidiaries
Net income (loss)	9,432us-gaap_NetIncomeLoss	(3,067)us-gaap_NetIncomeLoss	30,239us-gaap_NetIncomeLoss	15,593us-gaap_NetIncomeLoss
Foreign currency translation losses, net of tax	(458)	(226)	(726)	(286)
Comprehensive income (loss)	8,974us-gaap_ComprehensiveIncomeNetOfTax	(3,293)us-gaap_ComprehensiveIncomeNetOfTax	29,513us-gaap_ComprehensiveIncomeNetOfTax	15,307us-gaap_ComprehensiveIncomeNetOfTax
Parent
Revenues [Abstract]
Contract revenues	0	0	0	0
EXPENSES:
Costs of earned revenues, excluding depreciation and amortization	0	0	0	0
General and administrative	11,974	10,284	24,807	21,520
Depreciation and amortization	1,304	1,039	2,543	1,893
Intercompany charges (income), net	(15,009)	(13,130)	(30,831)	(27,106)
Interest expense, net	(1,731)	(1,807)	(3,481)	(3,696)
Other income, net	0	0	0	3
Income (loss) before income taxes	0	0	0	0
Provision (benefit) for income taxes:	0	0	0	0
Net income (loss) before equity in earnings of subsidiaries	0	0	0	0
Equity in earnings of subsidiaries	9,432	(3,067)	30,239	15,593
Net income (loss)	9,432	(3,067)	30,239	15,593
Foreign currency translation losses, net of tax	(458)	(226)	(726)	(286)
Comprehensive income (loss)	8,974	(3,293)	29,513	15,307
Issuer
Revenues [Abstract]
Contract revenues	0	0	0	0
EXPENSES:
Costs of earned revenues, excluding depreciation and amortization	0	0	0	0
General and administrative	140	215	239	441
Depreciation and amortization	0	0	0	0
Intercompany charges (income), net	0	0	0	0
Interest expense, net	(4,999)	(4,994)	(9,999)	(9,988)
Other income, net	0	0	0	0
Income (loss) before income taxes	(5,139)	(5,209)	(10,238)	(10,429)
Provision (benefit) for income taxes:	(2,027)	(2,102)	(4,036)	(4,189)
Net income (loss) before equity in earnings of subsidiaries	(3,112)	(3,107)	(6,202)	(6,240)
Equity in earnings of subsidiaries	12,544	40	36,441	21,833
Net income (loss)	9,432	(3,067)	30,239	15,593
Foreign currency translation losses, net of tax	(458)	(226)	(726)	(286)
Comprehensive income (loss)	8,974	(3,293)	29,513	15,307
Subsidiary Guarantors
Revenues [Abstract]
Contract revenues	437,970	388,402	943,659	897,832
EXPENSES:
Costs of earned revenues, excluding depreciation and amortization	353,182	325,678	753,274	733,373
General and administrative	26,502	25,322	54,671	54,266
Depreciation and amortization	20,789	21,230	41,370	42,851
Intercompany charges (income), net	15,515	13,271	31,923	27,380
Interest expense, net	0	1	0	(2)
Other income, net	1,913	630	3,694	2,575
Income (loss) before income taxes	23,895	3,532	66,115	42,535
Provision (benefit) for income taxes:	9,426	1,485	26,064	17,085
Net income (loss) before equity in earnings of subsidiaries	14,469	2,047	40,051	25,450
Equity in earnings of subsidiaries	0	0	(256)	0
Net income (loss)	14,469	2,047	39,795	25,450
Foreign currency translation losses, net of tax	0	0	0	0
Comprehensive income (loss)	14,469	2,047	39,795	25,450
Non- Guarantor Subsidiaries
Revenues [Abstract]
Contract revenues	3,111	2,116	7,811	5,406
EXPENSES:
Costs of earned revenues, excluding depreciation and amortization	2,247	1,675	5,624	4,099
General and administrative	3,199	2,741	6,794	5,410
Depreciation and amortization	1,171	1,166	2,280	2,243
Intercompany charges (income), net	(506)	(141)	(1,092)	(274)
Interest expense, net	0	0	0	0
Other income, net	(178)	(35)	(164)	29
Income (loss) before income taxes	(3,178)	(3,360)	(5,959)	(6,043)
Provision (benefit) for income taxes:	(1,253)	(1,353)	(2,349)	(2,426)
Net income (loss) before equity in earnings of subsidiaries	(1,925)	(2,007)	(3,610)	(3,617)
Equity in earnings of subsidiaries	0	0	0	0
Net income (loss)	(1,925)	(2,007)	(3,610)	(3,617)
Foreign currency translation losses, net of tax	(458)	(226)	(726)	(286)
Comprehensive income (loss)	(2,383)	(2,233)	(4,336)	(3,903)
Eliminations and Reclassifications
Revenues [Abstract]
Contract revenues	0	0	0	0
EXPENSES:
Costs of earned revenues, excluding depreciation and amortization	0	0	0	0
General and administrative	0	0	0	0
Depreciation and amortization	0	0	0	0
Intercompany charges (income), net	0	0	0	0
Interest expense, net	0	0	0	0
Other income, net	0	0	0	0
Income (loss) before income taxes	0	0	0	0
Provision (benefit) for income taxes:	0	0	0	0
Net income (loss) before equity in earnings of subsidiaries	0	0	0	0
Equity in earnings of subsidiaries	(21,976)	3,027	(66,424)	(37,426)
Net income (loss)	(21,976)	3,027	(66,424)	(37,426)
Foreign currency translation losses, net of tax	916	452	1,452	572
Comprehensive income (loss)	$ (21,060)	$ 3,479	$ (64,972)	$ (36,854)

Income (Loss) From Investment In Subsidiaries

No definition available.

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

- Definition

Intercompany charges (income) between parent, issuer, guarantor, and non-guarantor entities.

+ References

No definition available.

+ Details

Name:	dy_IntercompanyChargesIncome
Namespace Prefix:	dy_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Sum of operating profit and nonoperating income or expense before Income or Loss from equity method investment.

+ References

No definition available.

+ Details

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

- Definition

Amount after tax of increase (decrease) in equity from transactions and other events and circumstances from net income and other comprehensive income, attributable to parent entity. Excludes changes in equity resulting from investments by owners and distributions to owners.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Other Comprehensive Income

-URI http://asc.fasb.org/extlink&oid=6519514

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Comprehensive Income

-URI http://asc.fasb.org/extlink&oid=35737396

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 220

-SubTopic 10

-Section 45

-Paragraph 5

-URI http://asc.fasb.org/extlink&oid=36458714&loc=d3e557-108580

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Net Income

-URI http://asc.fasb.org/extlink&oid=6518256

+ Details

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

- Definition

The aggregate cost of services rendered during the reporting period, excluding depreciation, depletion and amortization.

+ References

No definition available.

+ Details

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

- Definition

The aggregate expense recognized in the current period that allocates the cost of tangible assets, intangible assets, or depleting assets to periods that benefit from use of the assets.

+ 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 (b)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585

+ Details

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

- Definition

The aggregate total of expenses of managing and administering the affairs of an entity, including affiliates of the reporting entity, which are not directly or indirectly associated with the manufacture, sale or creation of a product or product line.

+ References

+ Details

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

- Definition

Sum of operating profit and nonoperating income or expense before Income or Loss from equity method investments, income taxes, extraordinary items, and noncontrolling interest.

+ References

+ Details

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

- Definition

Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 235

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.4-08.(h))

-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 08

-Paragraph h

-Article 4

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Income Tax Expense (or Benefit)

-URI http://asc.fasb.org/extlink&oid=6515339

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section 50

-Paragraph 9

-Subparagraph (a),(b)

-URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32639-109319

+ Details

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

- Definition

The net amount of operating interest income (expense).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 225

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-04.10)

-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Paragraph 10

-Article 9

+ Details

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

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 260

-SubTopic 10

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Other Comprehensive Income

-URI http://asc.fasb.org/extlink&oid=6519514

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Net Income

-URI http://asc.fasb.org/extlink&oid=6518256

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 225

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-04.19)

-URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913

Reference 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.18)

-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688

Reference 7: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 225

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-04.22)

-URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913

Reference 8: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 19

-Article 5

Reference 9: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Paragraph 20

-Article 9

+ Details

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

- Details

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

- Definition

Amount after tax and reclassification adjustments of gain (loss) on foreign currency translation adjustments, foreign currency transactions designated and effective as economic hedges of a net investment in a foreign entity and intra-entity foreign currency transactions that are of a long-term-investment nature, attributable to parent entity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 810

-SubTopic 10

-Section 45

-Paragraph 20

-URI http://asc.fasb.org/extlink&oid=7656940&loc=SL4569643-111683

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 810

-SubTopic 10

-Section 45

-Paragraph 19

-URI http://asc.fasb.org/extlink&oid=7656940&loc=SL4569616-111683

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 810

-SubTopic 10

-Section 50

-Paragraph 1A

-Subparagraph (c)(3)

-URI http://asc.fasb.org/extlink&oid=18733093&loc=SL4573702-111684

+ Details

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

- Definition

The net amount of other income and expense amounts, the components of which are not separately disclosed on the income statement, resulting from ancillary business-related activities (that is, excluding major activities considered part of the normal operations of the business) also known as other nonoperating income (expense) recognized for the period. Such amounts may include: (a) dividends, (b) interest on securities, (c) net gains or losses on securities, (d) unusual costs, (e) gains or losses on foreign exchange transactions, and (f) miscellaneous other income and expense items.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 9

-Article 5

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.9)

-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688

+ Details

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

- Details

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

- Definition

Aggregate revenue during the period from services rendered in the normal course of business, after deducting allowances and discounts.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.1(d))

-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 1

-Article 5

+ Details

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

- Details

Name:	dei_LegalEntityAxis=dy_IssuerMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=us-gaap_ConsolidationEliminationsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=us-gaap_GuarantorSubsidiariesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=us-gaap_NonGuarantorSubsidiariesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=us-gaap_ParentCompanyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: