Note 13 - Condensed Consolidating Statements of Cash Flows (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Parent Company [Member]
Cash flows from operating activities	$ 7,848	$ 15,726
Investing activities:
Additions to properties, plants, equipment and mineral interests	$ (53)	$ (424)
Other investing activities, net
Financing activities:
Dividends paid to stockholders	$ (1,090)	$ (1,062)
Payments on debt
Other financing activity	$ (9,833)	$ (15,841)
Effect of exchange rates on cash
Changes in cash and cash equivalents	$ (3,128)	$ (1,601)
Cash and cash equivalents at beginning of period	94,167	146,885
Cash and cash equivalents at end of period	91,039	145,284
Cash flows from operating activities	7,848	15,726
Guarantor Subsidiaries [Member]
Cash flows from operating activities	(21,658)	15,823
Investing activities:
Additions to properties, plants, equipment and mineral interests	(18,552)	(18,163)
Other investing activities, net	$ 215	$ 25
Financing activities:
Dividends paid to stockholders
Payments on debt	$ (2,556)	$ (1,901)
Other financing activity	$ 27,189	$ 6,349
Effect of exchange rates on cash
Changes in cash and cash equivalents	$ (15,362)	$ 2,133
Cash and cash equivalents at beginning of period	42,692	33,824
Cash and cash equivalents at end of period	27,330	35,957
Cash flows from operating activities	(21,658)	15,823
Non-Guarantor Subsidiaries [Member]
Cash flows from operating activities	(7,884)	19,902
Investing activities:
Additions to properties, plants, equipment and mineral interests	(16,049)	(8,371)
Other investing activities, net	$ (3,900)	$ (947)
Financing activities:
Dividends paid to stockholders
Payments on debt	$ (226)	$ (446)
Other financing activity	23,823	(21,544)
Effect of exchange rates on cash	1,535	(2,560)
Changes in cash and cash equivalents	(2,701)	(13,966)
Cash and cash equivalents at beginning of period	18,350	28,956
Cash and cash equivalents at end of period	15,649	14,990
Cash flows from operating activities	(7,884)	19,902
Consolidation, Eliminations [Member]
Cash flows from operating activities	$ 40,442	$ (30,032)
Investing activities:
Additions to properties, plants, equipment and mineral interests
Other investing activities, net
Financing activities:
Dividends paid to stockholders
Payments on debt
Other financing activity	$ (40,442)	$ 30,032
Effect of exchange rates on cash
Changes in cash and cash equivalents
Cash and cash equivalents at beginning of period
Cash and cash equivalents at end of period
Cash flows from operating activities	$ 40,442	$ (30,032)
Consolidated [Member]
Cash flows from operating activities	18,748	21,419
Investing activities:
Additions to properties, plants, equipment and mineral interests	(34,654)	(26,958)
Other investing activities, net	(3,685)	(922)
Financing activities:
Dividends paid to stockholders	(1,090)	(1,062)
Payments on debt	(2,782)	(2,347)
Other financing activity	737	(1,004)
Effect of exchange rates on cash	1,535	(2,560)
Changes in cash and cash equivalents	(21,191)	(13,434)
Cash and cash equivalents at beginning of period	155,209	209,665
Cash and cash equivalents at end of period	134,018	196,231
Cash flows from operating activities	18,748	21,419
Cash flows from operating activities	18,748	21,419
Additions to properties, plants, equipment and mineral interests	(34,654)	(26,958)
Effect of exchange rates on cash	1,535	(2,560)
Changes in cash and cash equivalents	(21,191)	(13,434)
Cash and cash equivalents at beginning of period	155,209	209,665
Cash and cash equivalents at end of period	134,018	196,231
Cash flows from operating activities	$ 18,748	$ 21,419