Note 5 - Income Taxes - Net Deferred Tax Liability (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
Reserves and accrued liabilities	$ 7,277	$ 8,490
Other	1,965	2,757
	9,242	11,247
Deferred tax liabilities:
Depreciation	107,453	155,936
Prepaid expenses	2,415	3,165
	109,868	159,101
Net deferred tax liability	$ 100,626	$ 147,854