Note 14 - Unaudited Interim Condensed Consolidating Balance Sheets (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015	Jun. 30, 2015	Dec. 31, 2014
Parent Company [Member]
Assets
Cash and cash equivalents	$ 102,488	$ 94,167	$ 127,412	$ 146,885
Other current assets	41,498	15,972
Properties, plants, and equipment - net	2,266	2,281
Intercompany receivable (payable)	553,020	540,665
Investments in subsidiaries	1,247,747	1,252,191
Other non-current assets	2,518	2,200
Total assets	1,949,537	1,907,476
Liabilities and Stockholders' Equity
Current liabilities	21,820	21,087
Long-term debt	500,354	499,729
Non-current portion of accrued reclamation
Non-current deferred tax liability
Other non-current liabilities	47,685	47,734
Stockholders' equity	1,379,678	1,338,926
Total liabilities and stockholders' equity	1,949,537	1,907,476
Guarantor Subsidiaries [Member]
Assets
Cash and cash equivalents	23,720	42,692	55,906	33,824
Other current assets	95,009	58,453
Properties, plants, and equipment - net	1,167,053	1,147,770
Intercompany receivable (payable)	(342,822)	(301,291)
Investments in subsidiaries
Other non-current assets	177,907	165,080
Total assets	1,120,867	1,112,704
Liabilities and Stockholders' Equity
Current liabilities	82,221	84,559
Long-term debt	5,079	6,128
Non-current portion of accrued reclamation	43,381	45,494
Non-current deferred tax liability	13,293	3,264
Other non-current liabilities	5,937	5,834
Stockholders' equity	970,956	967,425
Total liabilities and stockholders' equity	1,120,867	1,112,704
Non-Guarantor Subsidiaries [Member]
Assets
Cash and cash equivalents	17,405	18,350	8,256	28,956
Other current assets	43,534	32,273
Properties, plants, and equipment - net	756,839	746,760
Intercompany receivable (payable)	(329,269)	(332,553)
Investments in subsidiaries
Other non-current assets	5,206	1,781
Total assets	493,715	466,611
Liabilities and Stockholders' Equity
Current liabilities	50,845	30,636
Long-term debt	2,237	3,183
Non-current portion of accrued reclamation	29,638	29,055
Non-current deferred tax liability	134,584	119,836
Other non-current liabilities	(380)	(865)
Stockholders' equity	276,791	284,766
Total liabilities and stockholders' equity	493,715	466,611
Consolidation, Eliminations [Member]
Assets
Cash and cash equivalents
Other current assets	(12,519)	7,626
Properties, plants, and equipment - net
Intercompany receivable (payable)	119,071	93,179
Investments in subsidiaries	(1,247,747)	(1,252,191)
Other non-current assets	(152,114)	(113,480)
Total assets	(1,293,309)	(1,264,866)
Liabilities and Stockholders' Equity
Current liabilities	(25,098)	(9,198)
Long-term debt
Non-current portion of accrued reclamation
Non-current deferred tax liability	(20,464)	(3,477)
Other non-current liabilities
Stockholders' equity	(1,247,747)	(1,252,191)
Total liabilities and stockholders' equity	(1,293,309)	(1,264,866)
Consolidated [Member]
Assets
Cash and cash equivalents	143,613	155,209	191,574	209,665
Other current assets	167,522	114,324
Properties, plants, and equipment - net	1,926,158	1,896,811
Intercompany receivable (payable)
Investments in subsidiaries
Other non-current assets	33,517	55,581
Total assets	2,270,810	2,221,925
Liabilities and Stockholders' Equity
Current liabilities	129,788	127,084
Long-term debt	507,670	509,040
Non-current portion of accrued reclamation	73,019	74,549
Non-current deferred tax liability	127,413	119,623
Other non-current liabilities	53,242	52,703
Stockholders' equity	1,379,678	1,338,926
Total liabilities and stockholders' equity	2,270,810	2,221,925
Cash and cash equivalents	143,613	155,209	$ 191,574	$ 209,665
Other current assets	7,999	9,453
Properties, plants, and equipment - net	1,926,158	1,896,811
Other non-current assets	3,638	2,783
Total assets	2,270,810	2,221,925
Current liabilities	129,788	127,084
Long-term debt	500,354	500,199
Non-current deferred tax liability	127,413	119,623
Other non-current liabilities	5,362	6,190
Stockholders' equity	1,379,678	1,338,926
Total liabilities and stockholders' equity	$ 2,270,810	$ 2,221,925