Note 13 - Guarantor Subsidiaries - Unaudited Interim Condensed Consolidating Statements of Operations (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Revenues	$ 166,355	$ 134,172	$ 303,280	$ 286,789
Cost of sales	(92,853)	(104,938)	(178,740)	(215,324)
Depreciation, depletion, amortization	(39,423)	(49,477)	(79,089)	(88,264)
General and administrative	(6,979)	(8,918)	(15,918)	(18,877)
Exploration and pre-development	(2,525)	(5,144)	(5,590)	(10,402)
Gain (loss) on derivative contracts	(14,002)	3,798	(6,109)	1,999
Acquisition costs	(6)	(397)	(11)	(410)
Equity in earnings of subsidiaries	0	0	0	0
Other expense	(23,969)	(26,649)	(49,472)	(45,410)
Income (loss) before income taxes	(13,402)	(57,711)	(31,649)	(90,460)
(Provision) benefit from income taxes	(626)	11,179	436	18,395
Net income (loss)	(14,028)	(46,532)	(31,213)	(72,065)
Series B Preferred Stock dividends declared	(138)	(138)	(276)	(276)
Income (loss) applicable to common stockholders	(14,166)	(46,670)	(31,489)	(72,341)
Changes in comprehensive income (loss)	10,384	3,540	(8,951)	7,799
Comprehensive income (loss)	(3,644)	(42,992)	(40,164)	(64,266)
Research and development	0	(158)	0	(561)
Reportable Legal Entities [Member] | Parent Company [Member]
Revenues	(4,998)	1,292	(3,319)	(1,185)
Cost of sales	(1,044)	(257)	(1,328)	(718)
Depreciation, depletion, amortization	0	0	0	0
General and administrative	(1,641)	(4,766)	(4,804)	(9,159)
Exploration and pre-development	(11)	(3)	(23)	(19)
Gain (loss) on derivative contracts	(14,002)	3,798	(6,109)	1,999
Acquisition costs	(6)	(163)	(11)	(121)
Equity in earnings of subsidiaries	(4,601)	(48,370)	6,729	(70,803)
Other expense	12,312	1,939	(22,311)	7,943
Income (loss) before income taxes	(13,991)	(46,530)	(31,176)	(72,063)
(Provision) benefit from income taxes	(37)	(2)	(37)	(2)
Net income (loss)	(14,028)	(46,532)	(31,213)	(72,065)
Series B Preferred Stock dividends declared	(138)	(138)	(276)	(276)
Income (loss) applicable to common stockholders	(14,166)	(46,670)	(31,489)	(72,341)
Changes in comprehensive income (loss)	10,384	3,540	(8,951)	7,799
Comprehensive income (loss)	(3,644)	(42,992)	(40,164)	(64,266)
Research and development		0		0
Reportable Legal Entities [Member] | Guarantor Subsidiaries [Member]
Revenues	166,420	121,846	291,736	264,340
Cost of sales	(88,705)	(95,235)	(167,456)	(194,568)
Depreciation, depletion, amortization	(38,528)	(47,629)	(76,721)	(84,656)
General and administrative	(4,789)	(3,738)	(10,128)	(8,849)
Exploration and pre-development	(1,745)	(3,268)	(3,800)	(6,330)
Gain (loss) on derivative contracts	0	0	0	0
Acquisition costs	0	(81)	0	(136)
Equity in earnings of subsidiaries	0	0	0	0
Other expense	(31,301)	(26,675)	(20,597)	(46,453)
Income (loss) before income taxes	1,352	(54,935)	13,034	(77,210)
(Provision) benefit from income taxes	(7,657)	2,558	(6,601)	2,496
Net income (loss)	(6,305)	(52,377)	6,433	(74,714)
Series B Preferred Stock dividends declared	0	0	0	0
Income (loss) applicable to common stockholders	(6,305)	(52,377)	6,433	(74,714)
Changes in comprehensive income (loss)	0	0	0	0
Comprehensive income (loss)	(6,305)	(52,377)	6,433	(74,714)
Research and development		(155)		(558)
Reportable Legal Entities [Member] | Non-Guarantor Subsidiaries [Member]
Revenues	4,933	11,034	14,863	23,634
Cost of sales	(3,104)	(9,446)	(9,956)	(20,038)
Depreciation, depletion, amortization	(895)	(1,848)	(2,368)	(3,608)
General and administrative	(549)	(414)	(986)	(869)
Exploration and pre-development	(769)	(1,873)	(1,767)	(4,053)
Gain (loss) on derivative contracts	0	0	0	0
Acquisition costs	0	(153)	0	(153)
Equity in earnings of subsidiaries	0	0	0	0
Other expense	2,325	525	1,584	1,932
Income (loss) before income taxes	1,941	(2,178)	1,370	(3,158)
(Provision) benefit from income taxes	(237)	6,184	(1,074)	7,069
Net income (loss)	1,704	4,006	296	3,911
Series B Preferred Stock dividends declared	0	0	0	0
Income (loss) applicable to common stockholders	1,704	4,006	296	3,911
Changes in comprehensive income (loss)	0	0	0	0
Comprehensive income (loss)	1,704	4,006	296	3,911
Research and development		(3)		(3)
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
Gain (loss) on derivative contracts	0	0	0	0
Acquisition costs	0	0	0	0
Equity in earnings of subsidiaries	4,601	48,370	(6,729)	70,803
Other expense	(7,305)	(2,438)	(8,148)	(8,832)
Income (loss) before income taxes	(2,704)	45,932	(14,877)	61,971
(Provision) benefit from income taxes	7,305	2,439	8,148	8,832
Net income (loss)	4,601	48,371	(6,729)	70,803
Series B Preferred Stock dividends declared	0	0	0	0
Income (loss) applicable to common stockholders	4,601	48,371	(6,729)	70,803
Changes in comprehensive income (loss)	0	0	0	0
Comprehensive income (loss)	$ 4,601	48,371	$ (6,729)	70,803
Research and development		$ 0		$ 0