Note 13 - Derivative Instruments (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Percent of Projected Fuel Requirements	6.00%	20.00%
Derivative Liability, Fair Value, Net			$ 0.5	$ 0.1
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net			3.1	1.9	1.8
Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months			$ 0.3
Gallons of Diesel [Member]
Derivative, Number of Instruments Held			12,100,000
Gallons of Diesel [Member]
Derivative, Number of Instruments Held		4,000,000