Note 11 - Other Comprehensive Income (Loss) ("OCI") - Components of AOCI (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Other comprehensive income (loss), reclassification adjustment from AOCI on derivatives, tax	$ (137)	$ (613)	$ (175)	$ (1,122)
Other comprehensive income (loss), reclassification adjustment from AOCI on derivatives, net of tax	363	$ (978)	461	$ (1,792)
Reclassification out of Accumulated Other Comprehensive Income [Member]
Other comprehensive income (loss), reclassification adjustment from AOCI on derivatives, before tax	33		96
Commodity Contract [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Other comprehensive income (loss), reclassification adjustment from AOCI on derivatives, net of tax	(387)		(531)
Commodity Contract [Member] | Fuel Expense [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Other comprehensive income (loss), reclassification adjustment from AOCI on derivatives, before tax	(533)		(732)
Commodity Contract [Member] | Income Tax Expense [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Other comprehensive income (loss), reclassification adjustment from AOCI on derivatives, tax	146		201
Interest Rate Cap [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Other comprehensive income (loss), reclassification adjustment from AOCI on derivatives, net of tax	24		70
Interest Rate Cap [Member] | Income Tax Expense [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Other comprehensive income (loss), reclassification adjustment from AOCI on derivatives, tax	$ (9)		$ (26)