Note 14 - Guarantor Subsidiaries - Unaudited Interim Condensed Consolidating Statements of Cash Flows (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Cash flows from operating activities	$ 63,609	$ 75,210
Additions to properties, plants, equipment and mineral interests	(97,338)	(83,285)
Other investing activities, net	1,457	38,023
Dividends paid to shareholders	(4,070)	(3,607)
Borrowings on debt	245,000	78,024
Payments on debt	(200,484)	(88,028)
Other financing activity, net	(2,825)	(2,069)
Effect of exchange rates on cash	257	(215)
Changes in cash, cash equivalents and restricted cash and cash equivalents	5,606	(125,273)
Cash, cash equivalents and restricted cash and cash equivalents at beginning of period	28,414	187,139
Cash, cash equivalents and restricted cash and cash equivalents at end of period	34,020	61,866
Acquisitions of businesses, net of cash acquired	0	(139,326)
Reportable Legal Entities [Member] | Parent Company [Member]
Cash flows from operating activities	(140,110)	(29,868)
Additions to properties, plants, equipment and mineral interests	0	20,710
Other investing activities, net	72,128	(398,101)
Dividends paid to shareholders	(4,070)	(3,607)
Borrowings on debt	245,000	78,024
Payments on debt	(195,000)	(47,000)
Other financing activity, net	34,769	443,372
Effect of exchange rates on cash	0	0
Changes in cash, cash equivalents and restricted cash and cash equivalents	12,717	(75,796)
Cash, cash equivalents and restricted cash and cash equivalents at beginning of period	6,266	103,877
Cash, cash equivalents and restricted cash and cash equivalents at end of period	18,983	28,081
Acquisitions of businesses, net of cash acquired		(139,326)
Reportable Legal Entities [Member] | Guarantor Subsidiaries [Member]
Cash flows from operating activities	92,042	88,853
Additions to properties, plants, equipment and mineral interests	(56,329)	(101,147)
Other investing activities, net	42	4,309
Dividends paid to shareholders	0	0
Borrowings on debt	0	0
Payments on debt	(4,965)	(41,028)
Other financing activity, net	(38,672)	26,051
Effect of exchange rates on cash	257	(215)
Changes in cash, cash equivalents and restricted cash and cash equivalents	(7,625)	(23,177)
Cash, cash equivalents and restricted cash and cash equivalents at beginning of period	18,258	46,619
Cash, cash equivalents and restricted cash and cash equivalents at end of period	10,633	23,442
Reportable Legal Entities [Member] | Non-Guarantor Subsidiaries [Member]
Cash flows from operating activities	(15,242)	(40,161)
Additions to properties, plants, equipment and mineral interests	(41,009)	(2,848)
Other investing activities, net	1,415	0
Dividends paid to shareholders	0	0
Borrowings on debt	0	0
Payments on debt	(519)	0
Other financing activity, net	55,869	16,709
Effect of exchange rates on cash	0
Changes in cash, cash equivalents and restricted cash and cash equivalents	514	(26,300)
Cash, cash equivalents and restricted cash and cash equivalents at beginning of period	3,890	36,643
Cash, cash equivalents and restricted cash and cash equivalents at end of period	4,404	10,343
Acquisitions of businesses, net of cash acquired		0
Consolidation, Eliminations [Member]
Cash flows from operating activities	126,919	56,386
Additions to properties, plants, equipment and mineral interests	0	0
Other investing activities, net	(72,128)	431,815
Dividends paid to shareholders	0	0
Borrowings on debt	0	0
Payments on debt	0	0
Other financing activity, net	(54,791)	(488,201)
Effect of exchange rates on cash	0	0
Changes in cash, cash equivalents and restricted cash and cash equivalents	0	0
Cash, cash equivalents and restricted cash and cash equivalents at beginning of period	0	0
Cash, cash equivalents and restricted cash and cash equivalents at end of period	$ 0	0
Acquisitions of businesses, net of cash acquired		$ 0