Note 7 - Hedging Program and Derivatives - Summary Position of Derivative Contracts (Details) - Oil - WTI [Member] bbl in Thousands	6 Months Ended
	Jun. 30, 2018 $ / bbl bbl
Fixed Swap, Contract Period 2018 July - December [Member]
Daily volume (Barrel of Oil) | bbl	4,238
Swap price (in USD per Barrel of Oil) | $ / bbl	53.7
Fixed Swap, Contract Period 2019 January - December [Member]
Daily volume (Barrel of Oil) | bbl	2,800
Swap price (in USD per Barrel of Oil) | $ / bbl	55.66
Fixed Swap, Contract Period 2020 January - December [Member]
Daily volume (Barrel of Oil) | bbl	2,200
Swap price (in USD per Barrel of Oil) | $ / bbl	54.34