Statements of Consolidated Income (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Income Statement [Abstract]
Revenue	$ 1,372,431us-gaap_Revenues	$ 1,368,843us-gaap_Revenues
Salaries, wages and employee benefits	564,307us-gaap_LaborAndRelatedExpense	537,252us-gaap_LaborAndRelatedExpense
Purchased transportation	331,934cnw_PurchasedTransportation	332,985cnw_PurchasedTransportation
Other operating expenses	167,105us-gaap_OtherCostAndExpenseOperating	162,236us-gaap_OtherCostAndExpenseOperating
Fuel and fuel-related taxes	86,903us-gaap_FuelCosts	136,702us-gaap_FuelCosts
Depreciation and amortization	59,963	59,611
Purchased labor	40,510cnw_PurchasedLabor	42,220cnw_PurchasedLabor
Rents and leases	35,927us-gaap_LeaseAndRentalExpense	33,959us-gaap_LeaseAndRentalExpense
Maintenance	33,855us-gaap_MaintenanceCosts	30,816us-gaap_MaintenanceCosts
Operating Expenses	1,320,504us-gaap_OperatingExpenses	1,335,781us-gaap_OperatingExpenses
Operating Income	51,927us-gaap_OperatingIncomeLoss	33,062us-gaap_OperatingIncomeLoss
Investment income	165us-gaap_InvestmentIncomeNet	161us-gaap_InvestmentIncomeNet
Interest expense	(13,277)us-gaap_InterestExpense	(13,306)us-gaap_InterestExpense
Miscellaneous, net	(2,420)us-gaap_OtherNonoperatingExpense	(695)us-gaap_OtherNonoperatingExpense
Other Income (Expense)	(15,532)us-gaap_OtherNonoperatingIncomeExpense	(13,840)us-gaap_OtherNonoperatingIncomeExpense
Income before income tax provision	36,395	19,222
Income tax provision	14,603us-gaap_IncomeTaxExpenseBenefit	6,329us-gaap_IncomeTaxExpenseBenefit
Net Income	$ 21,792us-gaap_NetIncomeLoss	$ 12,893us-gaap_NetIncomeLoss
Weighted average common shares outstanding, basic	57,634,382	56,957,433
Weighted average common shares outstanding, diluted	58,222,166	57,540,068
Earnings per common share, basic	$ 0.38us-gaap_EarningsPerShareBasic	$ 0.23us-gaap_EarningsPerShareBasic
Earnings per common share, diluted	$ 0.37us-gaap_EarningsPerShareDiluted	$ 0.22us-gaap_EarningsPerShareDiluted
Cash Dividends Declared per Common Share	$ 0.15	$ 0.10

Costs incurred for temporary contract labor.

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Costs incurred with outside service providers for the transportation of customer shipments.

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Aggregate dividends declared during the period for each share of common stock outstanding.

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Fuel costs incurred that are directly related to goods produced and sold and services rendered during the reporting period.

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Sum of operating profit and nonoperating income or expense before Income or Loss from equity method investments, income taxes, extraordinary items, and noncontrolling interest.

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Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Amount of rent expense incurred for leased assets, including but not limited to, furniture and equipment, that is not directly or indirectly associated with the manufacture, sale or creation of a product or product line.

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Generally recurring costs associated with normal operations except for the portion of these expenses which can be clearly related to production and included in cost of sales or services. Includes selling, general and administrative expense.

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