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Shareholders' Equity Common Stock Repurchase Program and Cash Dividend (Details) (USD $)
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Jul. 29, 2014
Equity [Abstract]        
Stock repurchase program, authorized amount $ 150,000,000us-gaap_StockRepurchaseProgramAuthorizedAmount1      
Common stock repurchased, shares 355,000us-gaap_StockRepurchasedDuringPeriodShares      
Common stock repurchased 16,800,000us-gaap_StockRepurchasedDuringPeriodValue      
Repurchases of common stock included in current liabilities $ 984,000cnw_RepurchasesofCommonStockIncludedinCurrentLiabilities $ 0cnw_RepurchasesofCommonStockIncludedinCurrentLiabilities $ 0cnw_RepurchasesofCommonStockIncludedinCurrentLiabilities  
Cash dividend per common share, changed from       $ 0.10cnw_CashDividendperCommonShareChangedFrom
Cash dividend per common share, changed to       $ 0.15cnw_CashDividendperCommonShareChangedTo