Note 14 - Guarantor Subsidiaries - Unaudited Interim Condensed Consolidating Statements of Operations (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Revenues	$ 134,172	$ 147,259	$ 286,789	$ 286,968
Cost of sales	(104,938)	(80,440)	(215,324)	(153,309)
Depreciation, depletion, amortization	(49,477)	(31,817)	(88,264)	(59,871)
General and administrative	(8,918)	(9,787)	(18,877)	(17,522)
Exploration and pre-development	(5,144)	(9,253)	(10,402)	(17,618)
Research and development	(158)	(2,337)	(561)	(3,773)
Gain on derivative contracts	3,798	16,804	1,999	20,811
Acquisition costs	(397)	(1,010)	(410)	(3,517)
Equity in earnings of subsidiaries	0	0	0	0
Other expense	(26,649)	(12,593)	(45,410)	(23,910)
Income (loss) before income taxes	(57,711)	12,501	(90,460)	21,509
(Provision) benefit from income taxes	11,179	(427)	18,395	(1,195)
Net income (loss)	(46,532)	12,074	(72,065)	20,314
Series B Preferred Stock dividends declared ($0.875 per share)	(138)	(138)	(276)	(276)
Income (loss) applicable to common stockholders	(46,670)	11,936	(72,341)	20,038
Changes in comprehensive income (loss)	3,540	(5,162)	7,799	(7,267)
Comprehensive income (loss)	(42,992)	6,912	(64,266)	13,048
Revenues	134,172	147,259	286,789	286,968
Gain on derivative contracts	3,798	16,804	1,999	20,811
Foreign exchange gain (loss)	(4,381)	2,476	(7,514)	5,068
Suspension costs	2,266	6,801	5,044	11,818
Other (expense) income	(26,649)	(12,593)	(45,410)	(23,910)
Reportable Legal Entities [Member] | Parent Company [Member]
Revenues	1,292	2,697	(1,185)	3,312
Cost of sales	(257)	(73)	(718)	402
Depreciation, depletion, amortization	0	0	0	0
General and administrative	(4,766)	(4,615)	(9,159)	(8,448)
Exploration and pre-development	(3)	(72)	(19)	(127)
Research and development	0	0	0	0
Gain on derivative contracts	3,798	16,804	1,999	20,811
Acquisition costs	(163)	(940)	(121)	(3,300)
Equity in earnings of subsidiaries	(48,370)	5,745	(70,803)	23,513
Other expense	1,939	(1,741)	7,943	(1,414)
Income (loss) before income taxes	(46,530)	12,074	(72,063)	20,314
(Provision) benefit from income taxes	(2)	0	(2)	0
Net income (loss)	(46,532)	12,074	(72,065)	20,314
Series B Preferred Stock dividends declared ($0.875 per share)	(138)	(138)	(276)	(276)
Income (loss) applicable to common stockholders	(46,670)	11,936	(72,341)	20,038
Changes in comprehensive income (loss)	3,540	(5,162)	7,799	(7,267)
Comprehensive income (loss)	(42,992)	6,912	(64,266)	13,048
Revenues	1,292	2,697	(1,185)	3,312
Gain on derivative contracts	3,798	16,804	1,999	20,811
Foreign exchange gain (loss)		(5,731)		(14,435)
Suspension costs		(0)		(0)
Other (expense) income	1,939	(1,741)	7,943	(1,414)
Reportable Legal Entities [Member] | Guarantor Subsidiaries [Member]
Revenues	76,213	75,197	178,645	145,408
Cost of sales	(58,994)	(37,489)	(125,863)	(72,190)
Depreciation, depletion, amortization	(29,068)	(11,996)	(49,940)	(23,256)
General and administrative	(3,738)	(4,602)	(8,849)	(8,050)
Exploration and pre-development	(2,097)	(3,064)	(3,641)	(5,003)
Research and development	(153)	(1,579)	(506)	(2,061)
Gain on derivative contracts	0	0	0	0
Acquisition costs	(81)	(68)	(136)	(68)
Equity in earnings of subsidiaries	0	0	0	0
Other expense	(6,091)	(1,616)	(11,821)	(3,393)
Income (loss) before income taxes	(24,009)	7,908	(22,111)	19,495
(Provision) benefit from income taxes	(2,859)	(3,715)	(6,775)	(9,203)
Net income (loss)	(26,868)	4,193	(28,886)	10,292
Series B Preferred Stock dividends declared ($0.875 per share)	0	0	0	0
Income (loss) applicable to common stockholders	(26,868)	4,193	(28,886)	10,292
Changes in comprehensive income (loss)	0	0	0	0
Comprehensive income (loss)	(26,868)	4,193	(28,886)	10,292
Revenues	76,213	75,197	178,645	145,408
Gain on derivative contracts	0	0	0	0
Foreign exchange gain (loss)		(74)		(74)
Suspension costs		6,801		11,818
Other (expense) income	(6,091)	(1,616)	(11,821)	(3,393)
Reportable Legal Entities [Member] | Non-Guarantor Subsidiaries [Member]
Revenues	56,667	69,365	109,329	138,248
Cost of sales	(45,687)	(42,878)	(88,743)	(81,521)
Depreciation, depletion, amortization	(20,409)	(19,821)	(38,324)	(36,615)
General and administrative	(414)	(570)	(869)	(1,024)
Exploration and pre-development	(3,044)	(6,117)	(6,742)	(12,488)
Research and development	(5)	(758)	(55)	(1,712)
Gain on derivative contracts	0	0	0	0
Acquisition costs	(153)	(2)	(153)	(149)
Equity in earnings of subsidiaries	0	0	0	0
Other expense	(20,058)	(5,522)	(32,700)	(9,901)
Income (loss) before income taxes	(33,103)	1,978	(58,257)	14,415
(Provision) benefit from income taxes	11,601	(426)	16,340	(1,194)
Net income (loss)	(21,502)	1,552	(41,917)	13,221
Series B Preferred Stock dividends declared ($0.875 per share)	0	0	0	0
Income (loss) applicable to common stockholders	(21,502)	1,552	(41,917)	13,221
Changes in comprehensive income (loss)	0	0	0	38
Comprehensive income (loss)	(21,502)	1,552	(41,917)	13,259
Revenues	56,667	69,365	109,329	138,248
Gain on derivative contracts	0	0	0	0
Foreign exchange gain (loss)		8,281		19,577
Suspension costs		(0)		(0)
Other (expense) income	(20,058)	(5,522)	(32,700)	(9,901)
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
Research and development	0	0	0	0
Gain on derivative contracts	0	0	0	0
Acquisition costs	0	0	0	0
Equity in earnings of subsidiaries	48,370	(5,745)	70,803	(23,513)
Other expense	(2,439)	(3,714)	(8,832)	(9,202)
Income (loss) before income taxes	45,931	(9,459)	61,971	(32,715)
(Provision) benefit from income taxes	2,439	3,714	8,832	9,202
Net income (loss)	48,370	(5,745)	70,803	(23,513)
Series B Preferred Stock dividends declared ($0.875 per share)	0	0	0	0
Income (loss) applicable to common stockholders	48,370	(5,745)	70,803	(23,513)
Changes in comprehensive income (loss)	0	0	0	(38)
Comprehensive income (loss)	48,370	(5,745)	70,803	(23,551)
Revenues	0	0	0	0
Gain on derivative contracts	0	0	0	0
Foreign exchange gain (loss)		0		0
Suspension costs		(0)		(0)
Other (expense) income	$ (2,439)	$ (3,714)	$ (8,832)	$ (9,202)