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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 | 5 dy_NumberOfCustomersClassifiedAsHighlyConcentrated |  | 5 dy_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 | 84.1 dy_ConcentrationRiskAmount / us-gaap_ConcentrationRiskByBenchmarkAxis = dy_TradeAccountsReceivableandCostsandEstimatedEarningsMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember / us-gaap_MajorCustomersAxis = dy_AttMember |  | 84.1 dy_ConcentrationRiskAmount / us-gaap_ConcentrationRiskByBenchmarkAxis = dy_TradeAccountsReceivableandCostsandEstimatedEarningsMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember / us-gaap_MajorCustomersAxis = dy_AttMember |  | $ 87.6 dy_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 | 46.7 dy_ConcentrationRiskAmount / us-gaap_ConcentrationRiskByBenchmarkAxis = dy_TradeAccountsReceivableandCostsandEstimatedEarningsMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember / us-gaap_MajorCustomersAxis = dy_CenturylinkMember |  | 46.7 dy_ConcentrationRiskAmount / us-gaap_ConcentrationRiskByBenchmarkAxis = dy_TradeAccountsReceivableandCostsandEstimatedEarningsMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember / us-gaap_MajorCustomersAxis = dy_CenturylinkMember |  | 48.2 dy_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 | 50.1 dy_ConcentrationRiskAmount / us-gaap_ConcentrationRiskByBenchmarkAxis = dy_TradeAccountsReceivableandCostsandEstimatedEarningsMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember / us-gaap_MajorCustomersAxis = dy_ComcastMember |  | 50.1 dy_ConcentrationRiskAmount / us-gaap_ConcentrationRiskByBenchmarkAxis = dy_TradeAccountsReceivableandCostsandEstimatedEarningsMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember / us-gaap_MajorCustomersAxis = dy_ComcastMember |  | $ 48.9 dy_ConcentrationRiskAmount / us-gaap_ConcentrationRiskByBenchmarkAxis = dy_TradeAccountsReceivableandCostsandEstimatedEarningsMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember / us-gaap_MajorCustomersAxis = dy_ComcastMember

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- 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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- Definition The number of customers classified as highly concentrated in comparison to total revenue. + References No definition available. + Details
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- 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 + Details
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