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Reconciliation of Basic and Diluted Loss Per Share Attributable to Common Stock (Detail) (USD $)
 3 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Income Per Common Share [Line Items]    
Net loss $ (4,991,000)us-gaap_NetIncomeLoss $ (2,897,000)us-gaap_NetIncomeLoss
Income allocable to unvested restricted stock (8,000)us-gaap_UndistributedEarningsLossAllocatedToParticipatingSecuritiesBasic  
Basic loss attributable to common stock (4,999,000)us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic (2,897,000)us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic
Reallocation of participating earnings 0dwsn_ReallocationOfNetIncomeAttributableToParticipatingSecurities 0dwsn_ReallocationOfNetIncomeAttributableToParticipatingSecurities
Diluted loss attributable to common stock $ (4,999,000)us-gaap_NetIncomeLossAvailableToCommonStockholdersDiluted $ (2,897,000)us-gaap_NetIncomeLossAvailableToCommonStockholdersDiluted
Weighted average common shares outstanding:    
Basic 7,965,757us-gaap_WeightedAverageNumberOfSharesOutstandingBasic 7,956,215us-gaap_WeightedAverageNumberOfSharesOutstandingBasic
Dilutive common stock options and restricted stock units 0us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustment 0us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustment
Diluted 7,965,757us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding 7,956,215us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding
Basic loss attributable to a share of common stock $ (0.63)us-gaap_EarningsPerShareBasic $ (0.36)us-gaap_EarningsPerShareBasic
Diluted loss attributable to a share of common stock $ (0.63)us-gaap_EarningsPerShareDiluted $ (0.36)us-gaap_EarningsPerShareDiluted