Note 14 - Income Taxes (Details Textual) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Income Tax Expense (Benefit), Total	$ (16,929)		$ 974	$ (26,866)	$ 310
Income Tax Expense (Benefit), Change in Tax Law	(1,800)	$ (3,900)
Income Tax Expense (Benefit), Discrete Tax Items				9,900	300
Income Tax Expense (Benefit), Exploration Abandonment		5,800
Impairment of Long-Lived Assets to be Disposed of	$ 94	$ 14,000	$ 14	$ 14,130	$ 19