Note 10 - Commitments and Contingencies (Details Textual) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Jun. 30, 2017	May 08, 2017	Dec. 31, 2016
Letters of Credit Outstanding, Amount		$ 30,900		$ 27,200
Cargo Claim [Member] | Judicial Ruling [Member]
Increase (Decrease) in Estimated Litigation Liability	$ 900
Estimated Litigation Liability			$ 7,200