Note 16 - Guarantor Subsidiaries - Unaudited Interim Condensed Consolidating Statements of Operations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenues	$ 673,266	$ 567,137	$ 577,775
Cost of sales	(450,349)	(353,994)	(304,727)
Depreciation, depletion, and amortization	(199,518)	(134,044)	(120,599)
General and administrative	(35,832)	(36,542)	(35,611)
Exploration and pre-development	(19,069)	(40,582)	(28,958)
Research and development	(535)	(5,441)	(3,276)
(Loss) gain on derivative contracts	(3,971)	40,253	(21,250)
Acquisition costs	(645)	(10,045)	(25)
Equity in earnings of subsidiaries	0	0	0
Other (expense) income	(87,005)	(60,006)	(70,886)
Income (loss) before income taxes	(123,658)	(33,264)	(7,557)
(Provision) benefit from income taxes	24,101	6,701	(20,963)
Net (loss) income	(99,557)	(26,563)	(28,520)
Series B Preferred Stock dividends declared	(552)	(552)	(552)
(Loss) income applicable to common stockholders	(100,109)	(27,115)	(29,072)
Changes in comprehensive (loss) income	5,159	(17,807)	11,229
Comprehensive (loss) income	(94,398)	(44,370)	(17,291)
Revenues	673,266	567,137	577,775
Other (expense) income	(87,005)	(60,006)	(70,886)
Other (expense) income	(87,005)	(60,006)	(70,886)
Loss applicable to common stockholders	(100,109)	(27,115)	(29,072)
Reportable Legal Entities [Member] | Parent Company [Member]
Revenues	(1,282)	8,084	(5,983)
Cost of sales	(1,948)	(446)	1,098
Depreciation, depletion, and amortization	0	0	0
General and administrative	(16,830)	(18,760)	(17,693)
Exploration and pre-development	(22)	(130)	(459)
Research and development	0	0	0
(Loss) gain on derivative contracts	(3,971)	40,253	(21,250)
Acquisition costs	(271)	(9,445)	(24)
Equity in earnings of subsidiaries	(76,385)	(47,226)	(187,574)
Other (expense) income	1,186	513	203,365
Income (loss) before income taxes	(99,523)	(27,157)	(28,520)
(Provision) benefit from income taxes	(34)	595	0
Net (loss) income	(99,557)	(26,562)	(28,520)
Series B Preferred Stock dividends declared	(552)	(552)	(552)
(Loss) income applicable to common stockholders	(100,109)	(27,114)	(29,072)
Changes in comprehensive (loss) income	5,159	(17,807)	11,229
Comprehensive (loss) income	(94,398)	(44,369)	(17,291)
Revenues	(1,282)	8,084	(5,983)
Other (expense) income	1,186	513	203,365
Other (expense) income	1,186	513	203,365
Loss applicable to common stockholders	(100,109)	(27,114)	(29,072)
Reportable Legal Entities [Member] | Guarantor Subsidiaries [Member]
Revenues	618,241	508,830	498,000
Cost of sales	(407,353)	(316,132)	(284,344)
Depreciation, depletion, and amortization	(189,746)	(129,442)	(117,906)
General and administrative	(17,350)	(15,963)	(15,889)
Exploration and pre-development	(13,191)	(30,332)	(19,892)
Research and development	(533)	(4,094)	(3,276)
(Loss) gain on derivative contracts	0	0	0
Acquisition costs	(221)	(344)	0
Equity in earnings of subsidiaries	0	0	0
Other (expense) income	(73,750)	(16,347)	(80,035)
Income (loss) before income taxes	(83,903)	(3,824)	(23,342)
(Provision) benefit from income taxes	7,941	(37,999)	(205,569)
Net (loss) income	(75,962)	(41,823)	(228,911)
Series B Preferred Stock dividends declared	0	0	0
(Loss) income applicable to common stockholders	(75,962)	(41,823)	(228,911)
Changes in comprehensive (loss) income	0	38	252
Comprehensive (loss) income	(75,962)	(41,785)	(228,659)
Revenues	618,241	508,830	498,000
Other (expense) income	(73,750)	(16,347)	(80,035)
Other (expense) income	(73,750)	(16,347)	(80,035)
Loss applicable to common stockholders	(75,962)	(41,823)	(228,911)
Reportable Legal Entities [Member] | Non-Guarantor Subsidiaries [Member]
Revenues	56,307	50,223	85,758
Cost of sales	(41,048)	(37,416)	(21,481)
Depreciation, depletion, and amortization	(9,772)	(4,602)	(2,693)
General and administrative	(1,652)	(1,819)	(2,029)
Exploration and pre-development	(5,856)	(10,120)	(8,607)
Research and development	(2)	(1,347)	0
(Loss) gain on derivative contracts	0	0	0
Acquisition costs	(153)	(256)	(1)
Equity in earnings of subsidiaries	0	0	0
Other (expense) income	2,161	3,258	8,298
Income (loss) before income taxes	(15)	(2,079)	59,245
(Provision) benefit from income taxes	(408)	(3,325)	(17,908)
Net (loss) income	(423)	(5,404)	41,337
Series B Preferred Stock dividends declared	0	0	0
(Loss) income applicable to common stockholders	(423)	(5,404)	41,337
Changes in comprehensive (loss) income	0	0	1,303
Comprehensive (loss) income	(423)	(5,404)	42,640
Revenues	56,307	50,223	85,758
Other (expense) income	2,161	3,258	8,298
Other (expense) income	2,161	3,258	8,298
Loss applicable to common stockholders	(423)	(5,404)	41,337
Consolidation, Eliminations [Member]
Revenues	0	0	0
Cost of sales	0	0	0
Depreciation, depletion, and amortization	0	0	0
General and administrative	0	0	0
Exploration and pre-development	0	0	0
Research and development	0	0	0
(Loss) gain on derivative contracts	0	0	0
Acquisition costs	0	0	0
Equity in earnings of subsidiaries	76,385	47,226	187,574
Other (expense) income	(16,602)	(47,430)	(202,514)
Income (loss) before income taxes	59,783	(204)	(14,940)
(Provision) benefit from income taxes	16,602	47,430	202,514
Net (loss) income	76,385	47,226	187,574
Series B Preferred Stock dividends declared	0	0	0
(Loss) income applicable to common stockholders	76,385	47,226	187,574
Changes in comprehensive (loss) income	0	(38)	(1,555)
Comprehensive (loss) income	76,385	47,188	186,019
Revenues	0	0	0
Other (expense) income	(16,602)	(47,430)	(202,514)
Other (expense) income	(16,602)	(47,430)	(202,514)
Loss applicable to common stockholders	$ 76,385	$ 47,226	$ 187,574