Note 7 - Debt (Details Textual) - USD ($)	1 Months Ended		3 Months Ended	9 Months Ended	12 Months Ended
	Aug. 31, 2015	Jul. 31, 2015	Sep. 30, 2015	Sep. 30, 2015	Dec. 31, 2014
Letter of Credit [Member]
Line of Credit Facility, Maximum Borrowing Capacity			$ 95,000,000	$ 95,000,000
Swing Line Sub Facility [Member]
Line of Credit Facility, Maximum Borrowing Capacity			$ 10,000,000	$ 10,000,000
Percent of Aggregate Commitments under Credit Facility			10.00%	10.00%
When Availability is at least 50 Million [Member]
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage		0.50%
Variable Rate Note [Member] | Interest Rate Swap [Member]
Derivative, Fixed Interest Rate	4.20%
Variable Rate Note [Member]
Debt Instrument, Fee Amount	$ 28,000,000
Interest Rate Swap [Member]
Derivative, Fixed Interest Rate	4.20%
Fixed Charge Coverage Requirement				$ 0	$ 0
Long-term Line of Credit			$ 0	0
Line of Credit Facility, Maximum Borrowing Capacity			95,000,000	95,000,000
Line of Credit Facility, Maximum Increase in Borrowing Capacity			$ 50,000,000	$ 50,000,000
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage	0.25%	0.375%	0.25%
Debt Instrument, Fee Amount	$ 100,000
Percent of Eligible Accounts Receivable				85.00%
Percent of Appraised Net Orderly Liquidation, Value of Eligible Revenue Equipment				85.00%
Percent of Net Book Value of Eligible Revenue Equipment				95.00%
Line of Credit Facility, Availability as Percentage of Revolver Commitment				35.00%
Line of Credit Facility, Revolver Commitment, Amount				$ 25,000,000
Percent of Appraised Fair Market Value of Eligible Real Estate				65.00%
Letters of Credit Outstanding, Amount			$ 33,400,000	$ 33,400,000	$ 34,300,000
Line of Credit Facility, Remaining Borrowing Capacity			61,600,000	61,600,000
Debt, Secured with a Cross Default Feature			203,300,000	203,300,000
Commodity Contract Asset, Current			$ 19,000,000	$ 19,000,000