Note 16 - Guarantor Subsidiaries (Details) - Condensed Consolidating Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Assets
Cash and cash equivalents	$ 155,209	$ 209,665	$ 212,175	$ 190,984
Other current assets	9,453	12,312
Properties, plants, and equipment - net	1,896,811	1,831,564
Other non-current assets	2,783	9,415
Total assets	2,221,925	2,262,064	2,232,119
Liabilities and Stockholders' Equity
Current liabilities	127,084	90,985
Long-term debt	500,199	498,479
Non-current deferred tax liability	119,623	153,300
Other non-current liabilities	6,190	9,709
Stockholders' equity	1,338,926	1,396,974	1,326,419	1,137,951
Total liabilities and stockholders' equity	2,221,925	2,262,064
Consolidation, Eliminations [Member]
Assets
Other current assets	7,626	27,433
Intercompany receivable (payable)	93,179	46,245
Investments in subsidiaries	(1,252,191)	(1,317,969)
Other non-current assets	(113,480)	(88,137)
Total assets	(1,264,866)	(1,332,428)
Liabilities and Stockholders' Equity
Current liabilities	(9,198)	(72)
Non-current deferred tax liability	(3,477)	(14,387)
Stockholders' equity	(1,252,191)	(1,317,969)
Total liabilities and stockholders' equity	(1,264,866)	(1,332,428)
Consolidated [Member]
Assets
Cash and cash equivalents	155,209	209,665	212,175	190,984
Other current assets	114,324	106,694
Properties, plants, and equipment - net	1,896,811	1,831,564
Other non-current assets	55,581	114,141
Total assets	2,221,925	2,262,064
Liabilities and Stockholders' Equity
Current liabilities	127,084	90,985
Long-term debt	509,040	512,129
Non-current portion of accrued reclamation	74,549	55,619
Non-current deferred tax liability	119,623	153,300
Other non-current liabilities	52,703	53,057
Stockholders' equity	1,338,926	1,396,974
Total liabilities and stockholders' equity	2,221,925	2,262,064
Parent Company [Member]
Assets
Cash and cash equivalents	94,167	146,885	126,271	132,266
Other current assets	15,972	7,115
Properties, plants, and equipment - net	2,281	1,572
Intercompany receivable (payable)	540,665	470,306
Investments in subsidiaries	1,252,191	1,317,969
Other non-current assets	2,200	8,644
Total assets	1,907,476	1,952,491
Liabilities and Stockholders' Equity
Current liabilities	21,087	14,143
Long-term debt	499,729	498,479
Other non-current liabilities	47,734	42,895
Stockholders' equity	1,338,926	1,396,974
Total liabilities and stockholders' equity	1,907,476	1,952,491
Guarantor Subsidiaries [Member]
Assets
Cash and cash equivalents	42,692	33,824	40,009	57,075
Other current assets	58,453	48,981
Properties, plants, and equipment - net	1,147,770	1,079,658
Intercompany receivable (payable)	(301,291)	(123,671)
Other non-current assets	165,080	189,014
Total assets	1,112,704	1,227,806
Liabilities and Stockholders' Equity
Current liabilities	84,559	54,918
Long-term debt	6,128	10,597
Non-current portion of accrued reclamation	45,494	43,314
Non-current deferred tax liability	3,264	14,387
Other non-current liabilities	5,834	11,126
Stockholders' equity	967,425	1,093,464
Total liabilities and stockholders' equity	1,112,704	1,227,806
Non-Guarantor Subsidiaries [Member]
Assets
Cash and cash equivalents	18,350	28,956	$ 45,895	$ 1,643
Other current assets	32,273	23,165
Properties, plants, and equipment - net	746,760	750,334
Intercompany receivable (payable)	(332,553)	(392,880)
Other non-current assets	1,781	4,620
Total assets	466,611	414,195
Liabilities and Stockholders' Equity
Current liabilities	30,636	21,996
Long-term debt	3,183	3,053
Non-current portion of accrued reclamation	29,055	12,305
Non-current deferred tax liability	119,836	153,300
Other non-current liabilities	(865)	(964)
Stockholders' equity	284,766	224,505
Total liabilities and stockholders' equity	$ 466,611	$ 414,195