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Concentration of Credit Risk (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended		3 Months Ended		12 Months Ended
	Jan. 24, 2015	Jan. 25, 2014	Jan. 24, 2015	Jan. 25, 2014	Jul. 26, 2014
Concentration Risk [Line Items]
Number of customers classified as highly concentrated	5dy_NumberOfCustomersClassifiedAsHighlyConcentrated		5dy_NumberOfCustomersClassifiedAsHighlyConcentrated
Customer Concentration Risk | Five Unnamed Customers
Concentration Risk [Line Items]
Concentration risk percentage	59.80%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember / us-gaap_MajorCustomersAxis = dy_FiveUnnamedCustomersMember	58.20%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember / us-gaap_MajorCustomersAxis = dy_FiveUnnamedCustomersMember
Sales Revenue, Services, Net | Customer Concentration Risk | AT&T Inc.
Concentration Risk [Line Items]
Concentration risk percentage	21.60%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueServicesNetMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember / us-gaap_MajorCustomersAxis = dy_AttMember	18.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueServicesNetMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember / us-gaap_MajorCustomersAxis = dy_AttMember	22.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueServicesNetMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember / us-gaap_MajorCustomersAxis = dy_AttMember	18.70%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueServicesNetMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember / us-gaap_MajorCustomersAxis = dy_AttMember
Sales Revenue, Services, Net | Customer Concentration Risk | CenturyLink, Inc.
Concentration Risk [Line Items]
Concentration risk percentage	13.50%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueServicesNetMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember / us-gaap_MajorCustomersAxis = dy_CenturylinkMember	15.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueServicesNetMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember / us-gaap_MajorCustomersAxis = dy_CenturylinkMember	14.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueServicesNetMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember / us-gaap_MajorCustomersAxis = dy_CenturylinkMember	14.40%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueServicesNetMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember / us-gaap_MajorCustomersAxis = dy_CenturylinkMember
Sales Revenue, Services, Net | Customer Concentration Risk | Comcast Corporation
Concentration Risk [Line Items]
Concentration risk percentage	12.90%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueServicesNetMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember / us-gaap_MajorCustomersAxis = dy_ComcastMember	11.20%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueServicesNetMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember / us-gaap_MajorCustomersAxis = dy_ComcastMember	13.10%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueServicesNetMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember / us-gaap_MajorCustomersAxis = dy_ComcastMember	12.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueServicesNetMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember / us-gaap_MajorCustomersAxis = dy_ComcastMember
Trade Accounts Receivable and Costs and Estimated Earnings | Customer Concentration Risk | AT&T Inc.
Concentration Risk [Line Items]
Concentration risk percentage	18.10%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = dy_TradeAccountsReceivableandCostsandEstimatedEarningsMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember / us-gaap_MajorCustomersAxis = dy_AttMember				17.90%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = dy_TradeAccountsReceivableandCostsandEstimatedEarningsMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember / us-gaap_MajorCustomersAxis = dy_AttMember
Accounts receivable, costs, and estimated earnings in excess of billings	84.1dy_ConcentrationRiskAmount / us-gaap_ConcentrationRiskByBenchmarkAxis = dy_TradeAccountsReceivableandCostsandEstimatedEarningsMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember / us-gaap_MajorCustomersAxis = dy_AttMember		84.1dy_ConcentrationRiskAmount / us-gaap_ConcentrationRiskByBenchmarkAxis = dy_TradeAccountsReceivableandCostsandEstimatedEarningsMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember / us-gaap_MajorCustomersAxis = dy_AttMember		$ 87.6dy_ConcentrationRiskAmount / us-gaap_ConcentrationRiskByBenchmarkAxis = dy_TradeAccountsReceivableandCostsandEstimatedEarningsMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember / us-gaap_MajorCustomersAxis = dy_AttMember
Trade Accounts Receivable and Costs and Estimated Earnings | Customer Concentration Risk | CenturyLink, Inc.
Concentration Risk [Line Items]
Concentration risk percentage	10.10%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = dy_TradeAccountsReceivableandCostsandEstimatedEarningsMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember / us-gaap_MajorCustomersAxis = dy_CenturylinkMember				9.80%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = dy_TradeAccountsReceivableandCostsandEstimatedEarningsMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember / us-gaap_MajorCustomersAxis = dy_CenturylinkMember
Accounts receivable, costs, and estimated earnings in excess of billings	46.7dy_ConcentrationRiskAmount / us-gaap_ConcentrationRiskByBenchmarkAxis = dy_TradeAccountsReceivableandCostsandEstimatedEarningsMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember / us-gaap_MajorCustomersAxis = dy_CenturylinkMember		46.7dy_ConcentrationRiskAmount / us-gaap_ConcentrationRiskByBenchmarkAxis = dy_TradeAccountsReceivableandCostsandEstimatedEarningsMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember / us-gaap_MajorCustomersAxis = dy_CenturylinkMember		48.2dy_ConcentrationRiskAmount / us-gaap_ConcentrationRiskByBenchmarkAxis = dy_TradeAccountsReceivableandCostsandEstimatedEarningsMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember / us-gaap_MajorCustomersAxis = dy_CenturylinkMember
Trade Accounts Receivable and Costs and Estimated Earnings | Customer Concentration Risk | Comcast Corporation
Concentration Risk [Line Items]
Concentration risk percentage	10.80%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = dy_TradeAccountsReceivableandCostsandEstimatedEarningsMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember / us-gaap_MajorCustomersAxis = dy_ComcastMember				9.90%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = dy_TradeAccountsReceivableandCostsandEstimatedEarningsMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember / us-gaap_MajorCustomersAxis = dy_ComcastMember
Accounts receivable, costs, and estimated earnings in excess of billings	50.1dy_ConcentrationRiskAmount / us-gaap_ConcentrationRiskByBenchmarkAxis = dy_TradeAccountsReceivableandCostsandEstimatedEarningsMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember / us-gaap_MajorCustomersAxis = dy_ComcastMember		50.1dy_ConcentrationRiskAmount / us-gaap_ConcentrationRiskByBenchmarkAxis = dy_TradeAccountsReceivableandCostsandEstimatedEarningsMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember / us-gaap_MajorCustomersAxis = dy_ComcastMember		$ 48.9dy_ConcentrationRiskAmount / us-gaap_ConcentrationRiskByBenchmarkAxis = dy_TradeAccountsReceivableandCostsandEstimatedEarningsMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember / us-gaap_MajorCustomersAxis = dy_ComcastMember

X

- Definition

Amount due from customers or clients, within one year of the balance sheet date (or the normal operating cycle, whichever is longer), for goods or services (including trade receivables) that have been delivered or sold in the normal course of business, reduced to the estimated net realizable fair value by an allowance established by the entity of the amount it deems uncertain of collection. This also includes the amount included in cost of uncompleted contracts in excess of related billings, or unbilled accounts receivable.

+ References

No definition available.

+ Details

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X

- Definition

The number of customers classified as highly concentrated in comparison to total revenue.

+ References

No definition available.

+ Details

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X

- Definition

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 21

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=35750535&loc=d3e13537-108611



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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 275

-SubTopic 10

-Section 50

-Paragraph 20

-URI http://asc.fasb.org/extlink&oid=6927468&loc=d3e6404-108592



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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 20

-URI http://asc.fasb.org/extlink&oid=35750535&loc=d3e13531-108611



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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 275

-SubTopic 10

-Section 50

-Paragraph 18

-URI http://asc.fasb.org/extlink&oid=6927468&loc=d3e6351-108592

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