Unaudited Condensed Consolidated Balance Sheets (Parentheticals) (USD $) In Thousands, except Per Share data, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Allowance for doubtful accounts of trade accounts receivable (in Dollars)	$ 2,504	$ 448
Accumulated depreciation of vessels and equipment (in Dollars)	453,880	420,355
Accumulated amortization of intangibles (in Dollars)	$ 18,018	$ 15,858
Preferred stock, shares authorized	2,000	2,000
Preferred stock, shares issued	0	0
Preferred stock, par value (in Dollars per share)	$ 0	$ 0
Common Class A [Member]
Common Stock, par value (in Dollars per share)	$ 0.01	$ 0.01
Common Stock, shares authorized	60,000	60,000
Common Stock, shares issued	27,276	27,165
Common Stock, shares outstanding	26,723	26,616
Common Class B [Member]
Common Stock, par value (in Dollars per share)	$ 0.01	$ 0.01
Common Stock, shares authorized	60,000	60,000
Common Stock, shares issued	0	0