Note 16 - Supplemental Oil and Gas Disclosures (Unaudited) - Oil and Gas Prices (Details)		12 Months Ended
		Dec. 31, 2018 $ / bbl $ / BTU	Dec. 31, 2017 $ / bbl $ / BTU	Dec. 31, 2016 $ / bbl $ / BTU
Oil (per Bbl) (1) (in USD per Barrel of Oil)	[1]	65.56	51.34	42.74
Gas (per MMbtu) (2) (in USD per British Thermal Unit) | $ / BTU	[2]	3.05	2.99	2.5
Oil (per Bbl) (3) (in USD per Barrel of Oil)	[3]	56.95	46.83	35.54
Gas (per MMbtu) (4) (in USD per British Thermal Unit) | $ / BTU	[4]	1.76	1.79	1.41
NGL's (per Bbl) (5) (in USD per Barrel of Oil)	[5]	19.95	13.19	5.17

[1] The quoted oil price for the year ended December 31 of each year, 2016, 2017 and 2018 is the 12-month unweighted average first-day-of-the-month West Texas Intermediate spot price for each month of 2016, 2017 and 2018.

[2] The quoted gas price for the year ended December 31, 2016, 2017 and 2018 is the 12-month unweighted average first-day-of-the-month Henry Hub spot price for each month of 2016, 2017 and 2018.

[3] The oil price is the realized price at the wellhead as of December 31 of each year after the appropriate differentials have been applied.

[4] The gas price is the realized price at the wellhead as of December 31 of each year after the appropriate differentials have been applied.

[5] The NGL price is the realized price as of December 31 of each year after the appropriate differentials have been applied.