Note 10 - Commitments and Contingencies (Details Textual) - USD ($)		1 Months Ended		3 Months Ended	6 Months Ended
	Aug. 26, 2014	Apr. 30, 2015	Sep. 30, 2014	Jun. 30, 2015	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Cargo Claim [Member]
Litigation Settlement, Amount	$ 5,900,000
Increase (Decrease) in Liability for Claims and Claims Adjustment Expense Reserve	$ 7,500,000		$ 8,100,000
Insurance Policy Term		3 years
Insurance Policy Primary Occurence Limit		$ 1,000,000
Loss Contingency, Range of Possible Loss, Maximum		$ 20,000,000
Refund on Commutation of Auto Liability Insurance Policy				$ 3,600,000	$ 3,600,000
Letters of Credit Outstanding, Amount				$ 33,400,000	$ 33,400,000		$ 34,300,000