Note 13 - Hedging Program and Derivatives - Summary Position of Derivative Contracts (Details) - Oil - WTI [Member]	12 Months Ended
	Dec. 31, 2018 $ / bbl bbl
Fixed Swap, Contract Period 2018 October - December [Member]
Daily volume (Barrel of Oil) | bbl	2,941
Swap price (in USD per Barrel of Oil) | $ / bbl	56.2
Fixed Swap, Contract Period 2019 January - December [Member]
Daily volume (Barrel of Oil) | bbl	2,204
Swap price (in USD per Barrel of Oil) | $ / bbl	54.35
Fixed Swap, Contract Period 2020 January - December [Member]
Daily volume (Barrel of Oil) | bbl	1,815
Swap price (in USD per Barrel of Oil) | $ / bbl	60.32
Fixed Swap, Contract Period 2021 January - December [Member]
Daily volume (Barrel of Oil) | bbl	4,000
Swap price (in USD per Barrel of Oil) | $ / bbl	2.98
Basis Swap, Contract Period 2019 January - December [Member]
Daily volume (Barrel of Oil) | bbl	4,000
Swap price (in USD per Barrel of Oil) | $ / bbl	2.98