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Investments in Debt and Equity Securities - Additional Information (Detail) (USD $)
In Thousands, unless otherwise specified
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Investments Debt And Equity Securities [Abstract]      
Available for sale investments gross pre-tax unrealized gain (loss) $ 5,181us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainLossBeforeTax $ 5,096us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainLossBeforeTax  
Unrealized gain (loss) on investments, pre tax 425us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodBeforeTax 3,752us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodBeforeTax  
Proceeds from sale of investments available-for-sale 1,262dva_ProceedsFromSaleOfAvailableForSaleSecuritiesPreviouslyRecordedInOCI 4,158dva_ProceedsFromSaleOfAvailableForSaleSecuritiesPreviouslyRecordedInOCI  
Pre tax reclassification of net investment realized gain (loss) into net income 340us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesBeforeTax 802us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesBeforeTax  
Reclassification of net investment realized gain (loss) into net income, net of tax $ 207us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesNetOfTax $ 490us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesNetOfTax $ 75us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesNetOfTax