Note 16 - Guarantor Subsidiaries (Details) - Condensed Consolidating Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Condensed Cash Flow Statements, Captions [Line Items]
Cash flows from operating activities	$ 106,445	$ 83,124	$ 26,644
Cash flows from investing activities:
Additions to properties, plants, and equipment	(137,443)	(122,537)	(150,736)
Acquisition of Aurizon Mines Ltd.	(809)		(321,117)
Cash flows from financing activities:
Borrowings on debt			490,000
Effect of exchange rates on cash	(5,152)	(3,783)	(4,905)
Changes in cash and cash equivalents	(54,456)	(2,510)	21,191
Cash and cash equivalents at beginning of year	209,665	212,175	190,984
Cash and cash equivalents at end of year	155,209	209,665	212,175
Consolidation, Eliminations [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Cash flows from operating activities	(2,629)	(75,323)	38,791
Cash flows from financing activities:
Other financing activity	2,629	75,323	(38,791)
Consolidated [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Cash flows from operating activities	106,445	83,124	26,644
Cash flows from investing activities:
Additions to properties, plants, and equipment	(137,443)	(122,537)	(150,736)
Acquisition of Aurizon Mines Ltd.			(321,117)
Other investing activities	(1,163)	4,182	(3,644)
Cash flows from financing activities:
Dividends paid to stockholders	(4,291)	(4,099)	(6,543)
Borrowings on debt			490,000
Payments on debt	(10,851)	(9,137)	(7,039)
Other financing activity	(2,001)	49,740	(1,469)
Effect of exchange rates on cash	(5,152)	(3,783)	(4,905)
Changes in cash and cash equivalents	(54,456)	(2,510)	21,191
Cash and cash equivalents at beginning of year	209,665	212,175	190,984
Cash and cash equivalents at end of year	155,209	209,665	212,175
Parent Company [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Cash flows from operating activities	(56,036)	38,270	(9,958)
Cash flows from investing activities:
Additions to properties, plants, and equipment	(1,355)	(1,336)	(1,535)
Acquisition of Aurizon Mines Ltd.			(498,705)
Other investing activities	(748)
Cash flows from financing activities:
Dividends paid to stockholders	(4,291)	(4,099)	(6,543)
Borrowings on debt			490,000
Other financing activity	9,712	(12,221)	20,746
Changes in cash and cash equivalents	(52,718)	20,614	(5,995)
Cash and cash equivalents at beginning of year	146,885	126,271	132,266
Cash and cash equivalents at end of year	94,167	146,885	126,271
Guarantor Subsidiaries [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Cash flows from operating activities	101,254	61,900	17,940
Cash flows from investing activities:
Additions to properties, plants, and equipment	(97,684)	(68,859)	(107,893)
Other investing activities	637	417	(11)
Cash flows from financing activities:
Payments on debt	(12,405)	(9,137)	(7,039)
Other financing activity	17,066	9,494	79,937
Changes in cash and cash equivalents	8,868	(6,185)	(17,066)
Cash and cash equivalents at beginning of year	33,824	40,009	57,075
Cash and cash equivalents at end of year	42,692	33,824	40,009
Non-Guarantor Subsidiaries [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Cash flows from operating activities	63,856	58,277	(20,129)
Cash flows from investing activities:
Additions to properties, plants, and equipment	(38,404)	(52,342)	(41,308)
Acquisition of Aurizon Mines Ltd.			177,588
Other investing activities	(1,052)	3,765	(3,633)
Cash flows from financing activities:
Payments on debt	1,554
Other financing activity	(31,408)	(22,856)	(63,361)
Effect of exchange rates on cash	(5,152)	(3,783)	(4,905)
Changes in cash and cash equivalents	(10,606)	(16,939)	44,252
Cash and cash equivalents at beginning of year	28,956	45,895	1,643
Cash and cash equivalents at end of year	$ 18,350	$ 28,956	$ 45,895