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Fair Value Measurements (Details) (USD $)
12 Months Ended
Dec. 31, 2013
Dec. 31, 2014
Fair Value Measurements    
Amount outstanding under revolving credit agreement $ 14,820,000us-gaap_LongTermLineOfCredit $ 10,760,000us-gaap_LongTermLineOfCredit
Long-lived assets held and used, losses 4,329,000us-gaap_AssetImpairmentCharges  
Fair Value, Measurements, Nonrecurring    
Fair Value Measurements    
Long-lived assets held and used, losses 4,329,000us-gaap_AssetImpairmentCharges
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
 
Estimate of Fair Value, Fair Value Disclosure    
Fair Value Measurements    
Available-for-sale securities 768,000us-gaap_AvailableForSaleSecurities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
820,000us-gaap_AvailableForSaleSecurities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
Estimate of Fair Value, Fair Value Disclosure | Fair Value, Measurements, Nonrecurring    
Fair Value Measurements    
Long-lived assets held and used   26,000,000dvd_AssetsHeldAndUsedLongLivedFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
Fair Value, Inputs, Level 1    
Fair Value Measurements    
Available-for-sale securities 768,000us-gaap_AvailableForSaleSecurities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
820,000us-gaap_AvailableForSaleSecurities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
Fair Value, Inputs, Level 3 | Fair Value, Measurements, Nonrecurring    
Fair Value Measurements    
Long-lived assets held and used   $ 26,000,000dvd_AssetsHeldAndUsedLongLivedFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember