Note 5 - Income Taxes (Details) - Net Deferred Tax Liability (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Deferred tax assets:
Reserves and accrued liabilities	$ 6,049	$ 6,051
Other	2,847us-gaap_DeferredTaxAssetsOther	2,796us-gaap_DeferredTaxAssetsOther
	8,896us-gaap_DeferredTaxAssetsGross	8,847us-gaap_DeferredTaxAssetsGross
Deferred tax liabilities:
Depreciation	125,697	116,438
Prepaid expenses	2,843	2,631
	128,540us-gaap_DeferredIncomeTaxLiabilities	119,069us-gaap_DeferredIncomeTaxLiabilities
Net deferred tax liability	$ 119,644us-gaap_DeferredTaxLiabilities	$ 110,222us-gaap_DeferredTaxLiabilities

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