Note 9 - Income Taxes (Details) - Deferred Tax Assets and Liabilities (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Deferred tax assets:
Insurance and claims	$ 16,153	$ 11,691
Net operating loss carryovers	18,160	13,681
Other	7,750us-gaap_DeferredTaxAssetsOther	6,035us-gaap_DeferredTaxAssetsOther
Deferred fuel hedge	8,144
Valuation allowance	(1,001)	(983)
Total deferred tax assets	49,206us-gaap_DeferredTaxAssetsNet	30,424us-gaap_DeferredTaxAssetsNet
Deferred tax liabilities:
Property and equipment	(103,186)	(76,280)
Other	(2,186)us-gaap_DeferredTaxLiabilitiesOther	(4,793)us-gaap_DeferredTaxLiabilitiesOther
Prepaid expenses	(2,838)	(3,194)
Total net deferred tax liabilities	(108,210)us-gaap_DeferredIncomeTaxLiabilities	(84,267)us-gaap_DeferredIncomeTaxLiabilities
Net deferred tax liability	$ (59,004)us-gaap_DeferredTaxLiabilities	$ (53,843)us-gaap_DeferredTaxLiabilities

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