Note 19 - Supplemental Oil and Gas Disclosures - Cost Incurred in Oil and Gas Property Acquisition Exploration and Development Activities (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Costs incurred: (1)
Proved properties acquisitions	[1]	$ 8.1	$ 223.8	$ 24.1
Exploration (2) (3)	[1],[2],[3]	7.4	30.6	49.9
Development	[1]	23.6	114.5	56.2
Total costs incurred in oil and gas property acquisition, exploration and development activities	[1]	$ 39.1	$ 368.9	$ 130.2

[1] Includes net additions from capitalized ARO of of $18.0 million, $37.5 million, and $20.3 million during 2020, 2019, and 2018, respectively. These adjustments for ARO are associated with acquisitions, liabilities incurred, divestitures and revisions of estimates.

[2] Includes geological and geophysical costs charged to expense of of $4.5 million, $5.7 million, and $5.4 million during 2020, 2019, and 2018, respectively.

[3] Includes seismic costs of $0.3 million, $7.8 million, and $1.5 million incurred during 2020, 2019, and 2018, respectively.