Note 6 - Derivative Instruments (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended		12 Months Ended
	Sep. 30, 2013	Sep. 30, 2013	Sep. 30, 2013 Gallons of Diesel [Member]	Dec. 31, 2015 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			3,700,000	3,000,000	13,100,000
Percent of Projected Fuel Requirements				4.70%	20.00%	23.00%
Derivative Liability, Fair Value, Amount Not Offset Against Collateral (in Dollars)	$ 0.2	$ 0.2
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net (in Dollars)	0.2	0.2
Derivative Instruments Not Designated as Hedging Instruments, Liability, at Fair Value (in Dollars)	0.1	0.1
Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months (in Dollars)		$ 0.2