Note 9 - Equity Method Investment (Details Textual) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	May 31, 2011
Proceeds from Sale of Property, Plant, and Equipment, Total	$ 61,687	$ 48,749	$ 65,507
Payments to Acquire Property, Plant, and Equipment, Total	75,142	110,802	112,794
Income (Loss) from Equity Method Investments, Total	7,732	3,400	3,000
Equity Method Investments	$ 26,106	20,145
Transport Enterprise Leasing LLC [Member]
Equity Method Investment, Ownership Percentage	49.00%			49.00%
Option to Acquire Interest in Equity Method Investment, Percentage of Ownership	51.00%
Proceeds from Sale of Property, Plant, and Equipment, Total	$ 100	100
Revenue from Related Parties	8,200	5,900
Payments to Acquire Property, Plant, and Equipment, Total	1,800
Payments for Rent	900	500
Deferred Gain on Sale of Property	200	200
Due from Related Parties, Total	7,200	8,600
Income (Loss) from Equity Method Investments, Total	7,700	3,400	3,000
Proceeds from Equity Method Investment, Distribution	2,000	2,000	$ 1,500
Equity Method Investments	26,100	20,100
Equity Method Investment, Aggregate Cost	4,900
Transport Enterprise Leasing LLC [Member] | Reduction in TEL Investment [Member]
Deferred Gain on Sale of Property	$ 200	$ 400