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Reconciliation of Basic and Diluted Earnings (Loss) Per Share Attributable to Common Stock (Detail) (USD $)
 3 Months Ended 12 Months Ended
Sep. 30, 2014
Jun. 30, 2014
Mar. 31, 2014
Dec. 31, 2013
Sep. 30, 2013
Jun. 30, 2013
Mar. 31, 2013
Dec. 31, 2012
Sep. 30, 2014
Sep. 30, 2013
Sep. 30, 2012
Income Per Common Share [Line Items]                      
Net (loss) income $ (3,882,000)us-gaap_NetIncomeLoss $ (7,493,000)us-gaap_NetIncomeLoss $ 1,652,000us-gaap_NetIncomeLoss $ (2,897,000)us-gaap_NetIncomeLoss $ (2,790,000)us-gaap_NetIncomeLoss $ 4,063,000us-gaap_NetIncomeLoss $ 6,279,000us-gaap_NetIncomeLoss $ 2,928,000us-gaap_NetIncomeLoss $ (12,620,000)us-gaap_NetIncomeLoss $ 10,480,000us-gaap_NetIncomeLoss $ 11,113,000us-gaap_NetIncomeLoss [1]
Income allocable to unvested restricted stock                 (25,000)us-gaap_UndistributedEarningsLossAllocatedToParticipatingSecuritiesBasic (136,000)us-gaap_UndistributedEarningsLossAllocatedToParticipatingSecuritiesBasic (158,000)us-gaap_UndistributedEarningsLossAllocatedToParticipatingSecuritiesBasic [1]
Basic (loss) income attributable to common stock                 (12,645,000)us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic 10,344,000us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic 10,955,000us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic [1]
Reallocation of participating earnings                   1,000dwsn_ReallocationOfNetIncomeAttributableToParticipatingSecurities  
Diluted (loss) income attributable to common stock                 $ (12,645,000)us-gaap_NetIncomeLossAvailableToCommonStockholdersDiluted $ 10,345,000us-gaap_NetIncomeLossAvailableToCommonStockholdersDiluted $ 10,955,000us-gaap_NetIncomeLossAvailableToCommonStockholdersDiluted [1]
Weighted average common shares outstanding:                      
Basic:                 7,959,452us-gaap_WeightedAverageNumberOfSharesOutstandingBasic 7,879,614us-gaap_WeightedAverageNumberOfSharesOutstandingBasic 7,841,722us-gaap_WeightedAverageNumberOfSharesOutstandingBasic [1]
Dilutive common stock options and restricted stock units                   40,751us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustment 35,385us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustment [1]
Diluted:                 7,959,452us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding 7,920,365us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding 7,877,107us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding [1]
Basic (loss) income attributable to a share of common stock $ (0.49)us-gaap_EarningsPerShareBasic $ (0.94)us-gaap_EarningsPerShareBasic $ 0.20us-gaap_EarningsPerShareBasic $ (0.36)us-gaap_EarningsPerShareBasic $ (0.35)us-gaap_EarningsPerShareBasic $ 0.50us-gaap_EarningsPerShareBasic $ 0.78us-gaap_EarningsPerShareBasic $ 0.36us-gaap_EarningsPerShareBasic $ (1.59)us-gaap_EarningsPerShareBasic $ 1.31us-gaap_EarningsPerShareBasic $ 1.40us-gaap_EarningsPerShareBasic [1]
Diluted (loss) income attributable to a share of common stock $ (0.49)us-gaap_EarningsPerShareDiluted $ (0.94)us-gaap_EarningsPerShareDiluted $ 0.20us-gaap_EarningsPerShareDiluted $ (0.36)us-gaap_EarningsPerShareDiluted $ (0.35)us-gaap_EarningsPerShareDiluted $ 0.50us-gaap_EarningsPerShareDiluted $ 0.78us-gaap_EarningsPerShareDiluted $ 0.36us-gaap_EarningsPerShareDiluted $ (1.59)us-gaap_EarningsPerShareDiluted $ 1.31us-gaap_EarningsPerShareDiluted $ 1.39us-gaap_EarningsPerShareDiluted [1]
Restricted stock                      
Weighted average common shares outstanding:                      
Nonvested restricted shares included in common stock outstanding 103,500us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember		       103,500us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember		       103,500us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember		 103,500us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember		 184,600us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
[1] The 2012 earnings per share calculations have been adjusted for the two-class method to reflect restricted shares that were not reflected as participating in the prior period. Basic earnings per share as previously reported for the year ended September 30, 2012 was $1.42. Diluted earnings per share as previously reported for the year ended September 30, 2012 was $1.40. Basic weighted average shares outstanding as previously reported for the year ended September 30, 2012 was 7,841,722. Diluted weighted average shares outstanding as previously reported for the year ended September 30, 2012 was 7,931,593. The impact on all prior period financial statements is deemed immaterial.