Note 15 - Asset Retirement Obligations - Reconciliation of the Beginning and Ending Aggregate Carrying Amount of Asset Retirement Obligation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Balance at beginning of year	$ 20,856	$ 19,142
Revision in estimated cash flows	303	(681)
Liabilities incurred	540	859
Accretion expense	1,649	1,536
Balance at end of year	$ 23,348	$ 20,856