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Accounting For Stock-Based Compensation (Narrative) (Details) (USD $)
In Millions, except Per Share data, unless otherwise specified
 3 Months Ended 6 Months Ended
Jan. 31, 2015
Jan. 31, 2014
Jan. 31, 2015
Jan. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Pre-tax stock-based compensation expense associated with stock options $ 5.6us-gaap_AllocatedShareBasedCompensationExpense $ 4.7us-gaap_AllocatedShareBasedCompensationExpense $ 6.9us-gaap_AllocatedShareBasedCompensationExpense $ 6.1us-gaap_AllocatedShareBasedCompensationExpense
Tax benefit associated with stock options 1.9us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense 1.6us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense 2.3us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense 2.0us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense
Weighted average fair value for options granted, per share     $ 9.95us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue $ 11.60us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue
Total intrinsic value of options exercised     13.4us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue 15.9us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue
Aggregate intrinsic value of options outstanding 63.7us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue   63.7us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue  
Aggregate intrinsic value of options exercisable 62.9us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1   62.9us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1  
Annual dividend yield     1.60%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate  
2010 Master Stock Incentive Plan [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Unrecognized compensation expense related to non-vested stock options granted $ 10.5us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized
/ us-gaap_PlanNameAxis
= dci_TwoThousandTenMasterStockIncentivePlanMember		   $ 10.5us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized
/ us-gaap_PlanNameAxis
= dci_TwoThousandTenMasterStockIncentivePlanMember		  
Minimum [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Options exercisable from date of the grant, in years     1 year  
Expected volatility     18.60%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate
/ us-gaap_RangeAxis
= us-gaap_MinimumMember		  
Risk-free interest rate     0.05%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate
/ us-gaap_RangeAxis
= us-gaap_MinimumMember		  
Maximum [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Options exercisable from date of the grant, in years     8 years  
Expected volatility     26.70%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate
/ us-gaap_RangeAxis
= us-gaap_MaximumMember		  
Risk-free interest rate     2.27%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate
/ us-gaap_RangeAxis
= us-gaap_MaximumMember