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Stock-Based Awards (Details) (USD $)
In Millions, except Share data, unless otherwise specified
 9 Months Ended 12 Months Ended
Apr. 25, 2015
Jul. 26, 2014
Stock Options    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Unrecognized compensation expense related to stock options $ 3.5us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember		  
Total compensation cost not yet recognized, period for recognition 2 years 8 months 12 days  
RSUs    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Unrecognized compensation expense related to stock options 6.9us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember		  
Total compensation cost not yet recognized, period for recognition 2 years 6 months  
Granted 100,360us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember		  
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number 350,746us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember		 398,931us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
Performance RSUs    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Unrecognized compensation expense related to stock options 15.5us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember		  
Total compensation cost not yet recognized, period for recognition 1 year 7 months 6 days  
Compensation expense $ 5.3dy_PotentialCompensationExpenseForPerformanceBasedSharesIfPerformanceGoalsAreMet
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember		  
RSUs outstanding 357,331dy_ShareBasedCompensationByShareBasedPaymentAwardEquityAwardsOtherThanOptionsTargetAmount
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember		  
Granted 416,987us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember		  
Forfeited or cancelled   312,163dy_SharebasedCompensationArrangementbySharebasedPaymentAwardEquityInstrumentsOtherthanOptionsCancelledinPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember
Share-based Compensation by Share-based Payment Award, Equity Awards Other than Options, Target Shares Expected to be Canceled   48,313dy_SharebasedCompensationbySharebasedPaymentAwardEquityAwardsOtherthanOptionsTargetSharesExpectedtobeCanceled
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember
Share-based Compensation by Share-based Payment Award, Equity Awards Other than Options, Supplemental Shares Expected to be Canceled   263,850dy_SharebasedCompensationbySharebasedPaymentAwardEquityAwardsOtherthanOptionsSupplementalSharesExpectedtobeCanceled
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number 955,286us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember		 1,190,184us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember
Target Shares    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number 725,438us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= dy_TargetSharesMember		  
Supplemental Shares    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Granted 59,656us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= dy_SupplementalSharesMember		  
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number 229,848us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= dy_SupplementalSharesMember