Note M - Leases (Details Textual) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Operating Lease, Payments	$ 100
Property, Plant and Equipment, Gross, Ending Balance	587,164		$ 563,162
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment, Ending Balance	184,316		$ 175,887
Depreciation, Total	14,295	$ 13,187
Trucks under Operating Lease [Member]
Property, Plant and Equipment, Gross, Ending Balance	60,800
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment, Ending Balance	28,200
Depreciation, Total	1,900
Accrued Expenses And Other Liabilities And Other Long-term Liabilities [Member]
Operating Lease, Liability, Total	1,963
Operating Lease, Right-of-Use Asset	1,963
Leases without Early Cancellation Options [Member] | Operating Lease Liabilities [Member]
Operating Lease, Liability, Total	2,000
Leases without Early Cancellation Options [Member] | Accrued Expenses And Other Liabilities And Other Long-term Liabilities [Member]
Operating Lease, Right-of-Use Asset	$ 2,000
Trucks under Operating Lease [Member]
Lessor, Operating Lease, Term of Contract (Year)	5 years
Minimum [Member] | Shop and Office Leases with Early Cancellation Options [Member]
Lessee, Operating Lease, Term of Contract (Year)	1 year
Minimum [Member] | Leases without Early Cancellation Options [Member]
Lessee, Operating Lease, Term of Contract (Year)	3 years
Maximum [Member] | Shop and Office Leases with Early Cancellation Options [Member]
Lessee, Operating Lease, Term of Contract (Year)	5 years
Maximum [Member] | Leases without Early Cancellation Options [Member]
Lessee, Operating Lease, Term of Contract (Year)			5 years