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Segment, Geographic and Customer Information - Additional Information (Detail)
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Segment Reporting Information [Line Items]      
Number of manufacturing facilities 68df_NumberOfManufacturingFacilities    
Number of reportable segments 1us-gaap_NumberOfReportableSegments    
Sales | Largest Customer      
Segment Reporting Information [Line Items]      
Percentage of sales 16.00%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_SalesMember
/ us-gaap_MajorCustomersAxis
= df_LargestCustomerMember		 19.00%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_SalesMember
/ us-gaap_MajorCustomersAxis
= df_LargestCustomerMember		 23.00%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_SalesMember
/ us-gaap_MajorCustomersAxis
= df_LargestCustomerMember
Sales | Foreign Operations      
Segment Reporting Information [Line Items]      
Percentage of sales 1.00%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_SalesMember
/ us-gaap_StatementBusinessSegmentsAxis
= df_ForeignOperationsMember		 1.00%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_SalesMember
/ us-gaap_StatementBusinessSegmentsAxis
= df_ForeignOperationsMember		 1.00%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_SalesMember
/ us-gaap_StatementBusinessSegmentsAxis
= df_ForeignOperationsMember