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Note 9 - Leases and Commitments (Details Textual) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Capital Lease Obligations, Total	$ 34,000		$ 34,000
Capital Lease Obligations, Current	8,014		8,014		$ 12,929
Capital Leases, Income Statement, Amortization Expense	1,200	$ 1,700	2,700	$ 3,600
Operating Leases, Rent Expense, Total	2,600	$ 3,100	5,600	5,600
Sale Leaseback Transaction, Net Proceeds, Investing Activities, Total				$ 10,980
Revenue and Non-revenue Equipment [Member]
Purchase Obligation, Total	$ 54,200		54,200
Sale-leaseback of Trailers to an Unrelated Party [Member]
Sale Leaseback Transaction, Net Proceeds, Investing Activities, Total			$ 5,300
Lessee, Operating Lease, Term of Contract	180 days		180 days
Sale Leaseback Transaction, Deferred Gain, Net, Total	$ 1,300		$ 1,300
Minimum [Member]
Capital Lease Term			1 year 90 days
Minimum [Member] \| Capital Lease Obligations [Member]
Debt Instrument, Interest Rate, Effective Percentage	0.00%		0.00%
Maximum [Member]
Capital Lease Term			5 years
Maximum [Member] \| Capital Lease Obligations [Member]
Debt Instrument, Interest Rate, Effective Percentage	3.11%		3.11%