Note 14 - Other Comprehensive Income ("OCI") - Components of AOCI (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
(Losses) gains on cash flow hedges
Other comprehensive income (loss), reclassification adjustment from AOCI on derivatives, before tax	$ (557)	$ (259)
Commodity Contract [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
(Losses) gains on cash flow hedges
Other comprehensive income (loss), reclassification adjustment from AOCI on derivatives, net of tax	(10,255)	(9,448)	(1,935)
Commodity Contract [Member] | Fuel Expense [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
(Losses) gains on cash flow hedges
Other comprehensive income (loss), reclassification adjustment from AOCI on derivatives, before tax	(16,674)	(15,313)	(3,141)
Commodity Contract [Member] | Income Tax Expense [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
(Losses) gains on cash flow hedges
Other comprehensive income (loss), reclassification adjustment from AOCI on derivatives, before tax	6,419	5,865	$ 1,206
Interest Rate Cap [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
(Losses) gains on cash flow hedges
Other comprehensive income (loss), reclassification adjustment from AOCI on derivatives, before tax	(342)	(160)
Interest Rate Cap [Member] | Income Tax Expense [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
(Losses) gains on cash flow hedges
Other comprehensive income (loss), reclassification adjustment from AOCI on derivatives, before tax	$ 215	$ 99