Summary of Significant Accounting Policies - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2012 Location
Significant Accounting Policies [Line Items]
Network of branch offices	276
Shared transactions between branches	Our branches work together to complete transactions and collectively meet the needs of our customers. For large multi-location customers, we often coordinate our efforts in one branch and rely on multiple branch locations to deliver specific geographic or modal needs. As an example, approximately 43 percent of our truckload transactions are shared transactions between branches.
Property and equipment, depreciation method	Depreciation is computed using the straight-line method over the estimated lives of the assets of 3 to 30 years.
Intangible assets, amortization method	These intangible assets are being amortized using the straight-line method over their estimated lives, ranging from three to five years.
Software
Significant Accounting Policies [Line Items]
Intangible assets, estimated lives (in years)	3 years
Intangible assets, amortization method	We amortize software using the straight-line method over three years.
Truckload Transactions
Significant Accounting Policies [Line Items]
Percentage of truckload transactions that are shared transactions between branches	43.00%
Minimum
Significant Accounting Policies [Line Items]
Property and equipment, estimated lives (in years)	3 years
Intangible assets, estimated lives (in years)	3 years
Restricted shares and restricted units grants, discount for post-vesting holding restrictions	12.00%
Maximum
Significant Accounting Policies [Line Items]
Property and equipment, estimated lives (in years)	30 years
Intangible assets, estimated lives (in years)	8 years
Restricted shares and restricted units grants, discount for post-vesting holding restrictions	22.00%