Note 6 - Derivative Instruments (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	6 Months Ended		12 Months Ended
	Jun. 30, 2013	Jun. 30, 2013	Jun. 30, 2013 Gallons of Diesel [Member]	Dec. 31, 2014 Gallons of Diesel [Member]	Dec. 31, 2013 Gallons of Diesel [Member]
Note 6 - Derivative Instruments (Details) [Line Items]
Derivative, Number of Instruments Held			7,000,000	12,100,000
Percent of Projected Fuel Requirements				19.00%	22.00%
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	$ 1.4	$ 1.4
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	0.20	0.01
Derivative, Net Hedge Ineffectiveness Gain (Loss)	(0.1)	(0.1)
Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months		$ 0.4