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Summary (Detail)
 12 Months Ended
Sep. 30, 2014
Sep. 30, 2013
Sep. 30, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Unvested restricted stock 103,500dwsn_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageNumberOfShares 169,649dwsn_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageNumberOfShares 113,426dwsn_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageNumberOfShares