Note 17 - Guarantor Subsidiaries - Unaudited Interim Condensed Consolidating Balance Sheets (Details) - USD ($) $ in Thousands		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2016	Dec. 31, 2015
Assets
Cash and cash equivalents		$ 27,389	$ 186,107
Other current assets		136,761	135,129
Properties, plants, and equipment - net	[1]	2,520,004	1,999,311
Intercompany receivable (payable)
Investments in subsidiaries
Other non-current assets		19,790	24,611
Total assets	[2]	2,703,944	2,345,158	$ 2,355,795
Liabilities and Stockholders' Equity
Current liabilities		136,194	112,130
Long-term debt		540,670	508,422
Non-current portion of accrued reclamation		104,979	79,366
Non-current deferred tax liability		173,537	124,352
Other non-current liabilities		57,601	59,611
Stockholders' equity		1,690,963	1,461,277	$ 1,462,240	$ 1,329,300	$ 1,329,300
Total liabilities and shareholders' equity		2,703,944	2,345,158
Reportable Legal Entities [Member] | Parent Company [Member]
Assets
Cash and cash equivalents		6,265	103,878
Other current assets		6,388	47,555
Properties, plants, and equipment - net		1,913	1,946
Intercompany receivable (payable)		171,905	287,310
Investments in subsidiaries		1,577,564	1,358,025
Other non-current assets		276,641	14,409
Total assets		2,040,676	1,813,123
Liabilities and Stockholders' Equity
Current liabilities		(234,133)	(226,576)
Long-term debt		532,799	502,229
Non-current portion of accrued reclamation
Non-current deferred tax liability
Other non-current liabilities		51,047	53,588
Stockholders' equity		1,690,963	1,483,882
Total liabilities and shareholders' equity		2,040,676	1,813,123
Reportable Legal Entities [Member] | Guarantor Subsidiaries [Member]
Assets
Cash and cash equivalents		8,661	31,016
Other current assets		69,574	47,608
Properties, plants, and equipment - net		1,795,994	1,244,161
Intercompany receivable (payable)		(222,815)	(177,438)
Investments in subsidiaries
Other non-current assets		9,030	7,289
Total assets		1,660,444	1,152,636
Liabilities and Stockholders' Equity
Current liabilities		118,863	66,550
Long-term debt		141,870	2,303
Non-current portion of accrued reclamation		94,602	67,565
Non-current deferred tax liability		64,639	10,120
Other non-current liabilities		5,659	5,185
Stockholders' equity		1,234,811	1,000,913
Total liabilities and shareholders' equity		1,660,444	1,152,636
Reportable Legal Entities [Member] | Non-Guarantor Subsidiaries [Member]
Assets
Cash and cash equivalents		12,463	51,213
Other current assets		60,868	40,541
Properties, plants, and equipment - net		722,097	753,204
Intercompany receivable (payable)		(171,834)	(341,182)
Investments in subsidiaries
Other non-current assets		(122,969)	9,283
Total assets		500,625	513,059
Liabilities and Stockholders' Equity
Current liabilities		45,922	37,671
Long-term debt		1,989	3,890
Non-current portion of accrued reclamation		10,377	11,801
Non-current deferred tax liability		98,689	124,352
Other non-current liabilities		895	838
Stockholders' equity		342,753	334,507
Total liabilities and shareholders' equity		500,625	513,059
Consolidation, Eliminations [Member]
Assets
Cash and cash equivalents
Other current assets		(69)	(575)
Properties, plants, and equipment - net
Intercompany receivable (payable)		222,744	231,310
Investments in subsidiaries		(1,577,564)	(1,358,025)
Other non-current assets		(142,912)	(6,370)
Total assets		(1,497,801)	(1,133,660)
Liabilities and Stockholders' Equity
Current liabilities		205,542	234,485
Long-term debt		(135,988)
Non-current portion of accrued reclamation
Non-current deferred tax liability		10,209	(10,120)
Other non-current liabilities
Stockholders' equity		(1,577,564)	(1,358,025)
Total liabilities and shareholders' equity		$ (1,497,801)	$ (1,133,660)

[1] Amounts reported as of and for the years ended December 31, 2017 and 2016 have been revised. See Note 2 for more information.

[2] Amounts reported as of and for the years ended December 31, 2017 and 2016 have been revised. See Note 2 for more information.