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Condensed Consolidated Statement Of Stockholders' Equity (Parenthetical) (USD $)
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Statement of Stockholders' Equity [Abstract]      
Issuance of common stock (in shares) 476,047us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised 681,426us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised 550,352us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised
Issuance of deferred stock units (in shares) 43,188dw_IssuanceOfDeferredStockUnitsShares 3,776dw_IssuanceOfDeferredStockUnitsShares 7,548dw_IssuanceOfDeferredStockUnitsShares
Special cash dividend, per share   $ 2us-gaap_CommonStockDividendsPerShareDeclared $ 2.00us-gaap_CommonStockDividendsPerShareDeclared