Note M - Leases (Details Textual) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	May 30, 2019	Dec. 31, 2018
Lessee, Operating Lease, Renewal Term	1 year		1 year		5 years
Lessee, Operating Lease, Term of Contract					5 years
Operating Lease, Right-of-Use Asset	$ 1,299		$ 1,299
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	1,300
Operating Lease, Payments	$ 100
Lessor, Operating Lease, Term of Contract	5 years		5 years
Property, Plant and Equipment, Gross, Ending Balance	$ 518,305		$ 518,305			$ 492,325
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment, Ending Balance	156,061		156,061			$ 137,738
Depreciation, Total	13,614	$ 12,734	26,801	$ 24,358
Operating Lease, Liability, Total	1,299		1,299
Trucks under Operating Lease [Member]
Property, Plant and Equipment, Gross, Ending Balance	57,400		57,400
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment, Ending Balance	26,700		$ 26,700
Depreciation, Total	$ 1,600
Minimum [Member]
Lessee, Operating Lease, Term of Contract	1 year		1 year
Maximum [Member]
Lessee, Operating Lease, Term of Contract	5 years		5 years