Note 2 - Revenue Recognition - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Oil Revenue [Member]
Revenue from Contract with Customer	$ 2,786	$ 3,942
Oil Revenue [Member] | Operated [Member]
Revenue from Contract with Customer	2,711	3,799
Oil Revenue [Member] | Non-operated [Member]
Revenue from Contract with Customer	75	143
Gas Revenue [Member]
Revenue from Contract with Customer	26,356	7,897
Gas Revenue [Member] | Operated [Member]
Revenue from Contract with Customer	20,174	5,801
Gas Revenue [Member] | Non-operated [Member]
Revenue from Contract with Customer	6,182	2,096
NGL Revenue [Member]
Revenue from Contract with Customer	4	4
NGL Revenue [Member] | Operated [Member]
Revenue from Contract with Customer
NGL Revenue [Member] | Non-operated [Member]
Revenue from Contract with Customer	4	4
Oil and Gas [Member]
Revenue from Contract with Customer	29,146	11,843
Oil and Gas [Member] | Operated [Member]
Revenue from Contract with Customer	22,885	9,600
Oil and Gas [Member] | Non-operated [Member]
Revenue from Contract with Customer	$ 6,261	$ 2,243