Note 8 - Income Taxes - Deferred Tax Liabilities and Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Hedge contracts	$ 3,167
Assets held for sale			3,390
Other	2,977	2,834	4,431
Total deferred tax liabilities	6,144	2,834	7,821
Oil and gas properties	4,310	20,011	48,436
Capital loss carryforwards	3,980	3,015	7,361
Depletion carryforward	3,098	3,174	5,216
U.S. net operating loss carryforward	61,309	53,545	80,670
Alternative minimum tax credit	757	757	757
Hedge contracts		2,777	3,135
Total deferred tax assets	73,454	83,279	145,575
Valuation allowance for deferred tax assets	(67,310)	(80,445)	(137,754)
Net deferred tax assets	6,144	2,834	7,821
Net deferred tax