Note 13 - Guarantor Subsidiaries - Unaudited Interim Condensed Consolidating Statements of Operations (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Revenues	$ 199,703	$ 161,532	$ 502,983	$ 448,321
Cost of sales	(105,977)	(95,878)	(284,717)	(311,202)
Depreciation, depletion, amortization	(40,238)	(50,774)	(119,327)	(139,038)
General and administrative	(11,713)	(7,978)	(27,631)	(26,855)
Exploration and pre-development	(4,166)	(5,689)	(9,756)	(16,091)
Loss on derivative contracts	(6,666)	(4,718)	(12,775)	(2,719)
Acquisition costs	(2)	(183)	(13)	(593)
Equity in earnings of subsidiaries	0	0	0	0
Other (expense) income	(15,680)	(17,389)	(65,152)	(62,799)
Income (loss) before income taxes	15,261	(21,130)	(16,388)	(111,590)
(Provision) benefit from income taxes	(1,633)	1,614	(1,197)	20,009
Net income (loss)	13,628	(19,516)	(17,585)	(91,581)
Series B Preferred Stock dividends declared	(138)	(138)	(414)	(414)
Income (loss) applicable to common shareholders	13,490	(19,654)	(17,999)	(91,995)
Changes in comprehensive income (loss)	6,150	(3,288)	(2,801)	4,511
Comprehensive income (loss)	19,778	(22,804)	(20,386)	(87,070)
Research and development	0	(53)	0	(614)
Reportable Legal Entities [Member] | Parent Company [Member]
Revenues	(9,558)	1,049	(12,877)	(136)
Cost of sales	(1,268)	(472)	(2,596)	(1,190)
Depreciation, depletion, amortization	0	0	0	0
General and administrative	(4,716)	(2,951)	(9,520)	(12,110)
Exploration and pre-development	(2)	(3)	(25)	(22)
Loss on derivative contracts	(6,666)	(4,718)	(12,775)	(2,719)
Acquisition costs	(2)	(100)	(13)	(221)
Equity in earnings of subsidiaries	21,895	(6,761)	28,624	(77,563)
Other (expense) income	14,066	(5,560)	(8,245)	2,382
Income (loss) before income taxes	13,749	(19,516)	(17,427)	(91,579)
(Provision) benefit from income taxes	(121)	0	(158)	(2)
Net income (loss)	13,628	(19,516)	(17,585)	(91,581)
Series B Preferred Stock dividends declared	(138)	(138)	(414)	(414)
Income (loss) applicable to common shareholders	13,490	(19,654)	(17,999)	(91,995)
Changes in comprehensive income (loss)	6,150	(3,288)	(2,801)	4,511
Comprehensive income (loss)	19,778	(22,804)	(20,386)	(87,070)
Research and development		0		0
Reportable Legal Entities [Member] | Guarantor Subsidiaries [Member]
Revenues	200,124	144,999	491,860	409,339
Cost of sales	(99,530)	(85,829)	(266,986)	(280,397)
Depreciation, depletion, amortization	(39,457)	(47,448)	(116,178)	(132,104)
General and administrative	(6,688)	(4,722)	(16,816)	(13,571)
Exploration and pre-development	(2,977)	(4,315)	(6,777)	(10,645)
Loss on derivative contracts	0	0	0	0
Acquisition costs	0	(83)	0	(219)
Equity in earnings of subsidiaries	0	0	0	0
Other (expense) income	(19,594)	(8,523)	(40,191)	(54,975)
Income (loss) before income taxes	31,878	(5,884)	44,912	(83,093)
(Provision) benefit from income taxes	(13,211)	(625)	(19,812)	6,864
Net income (loss)	18,667	(6,509)	25,100	(76,229)
Series B Preferred Stock dividends declared	0	0	0	0
Income (loss) applicable to common shareholders	18,667	(6,509)	25,100	(76,229)
Changes in comprehensive income (loss)	0	0	0	0
Comprehensive income (loss)	18,667	(6,509)	25,100	(76,229)
Research and development		37		(521)
Reportable Legal Entities [Member] | Non-Guarantor Subsidiaries [Member]
Revenues	9,137	15,484	24,000	39,118
Cost of sales	(5,179)	(9,577)	(15,135)	(29,615)
Depreciation, depletion, amortization	(781)	(3,326)	(3,149)	(6,934)
General and administrative	(309)	(305)	(1,295)	(1,174)
Exploration and pre-development	(1,187)	(1,371)	(2,954)	(5,424)
Loss on derivative contracts	0	0	0	0
Acquisition costs	0	0	0	(153)
Equity in earnings of subsidiaries	0	0	0	0
Other (expense) income	2,298	451	3,882	2,383
Income (loss) before income taxes	3,979	1,266	5,349	(1,892)
(Provision) benefit from income taxes	(751)	(1,518)	(1,825)	558
Net income (loss)	3,228	(252)	3,524	(1,334)
Series B Preferred Stock dividends declared	0	0	0	0
Income (loss) applicable to common shareholders	3,228	(252)	3,524	(1,334)
Changes in comprehensive income (loss)	0	0	0	0
Comprehensive income (loss)	3,228	(252)	3,524	(1,334)
Research and development		(90)		(93)
Consolidation, Eliminations [Member]
Revenues	0	0	0	0
Cost of sales	0	0	0	0
Depreciation, depletion, amortization	0	0	0	0
General and administrative	0	0	0	0
Exploration and pre-development	0	0	0	0
Loss on derivative contracts	0	0	0	0
Acquisition costs	0	0	0	0
Equity in earnings of subsidiaries	(21,895)	6,761	(28,624)	77,563
Other (expense) income	(12,450)	(3,757)	(20,598)	(12,589)
Income (loss) before income taxes	(34,345)	3,004	(49,222)	64,974
(Provision) benefit from income taxes	12,450	3,757	20,598	12,589
Net income (loss)	(21,895)	6,761	(28,624)	77,563
Series B Preferred Stock dividends declared	0	0	0	0
Income (loss) applicable to common shareholders	(21,895)	6,761	(28,624)	77,563
Changes in comprehensive income (loss)	0	0	0	0
Comprehensive income (loss)	$ (21,895)	6,761	$ (28,624)	77,563
Research and development		$ 0		$ 0