Note 16 - Guarantor Subsidiaries (Details) - Condensed Consolidating Balance Sheets (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Assets
Cash and cash equivalents	$ 209,665	$ 212,175	$ 190,984	$ 266,463
Other current assets	12,312	8,324
Properties, plants, and equipment - net	1,831,564	1,791,601
Other non-current assets	9,415	5,867
Total assets	2,262,064	2,232,119	1,378,290
Liabilities and Stockholders' Equity
Current liabilities	90,985	151,479
Long-term debt	498,479	490,726
Non-current deferred tax liability	153,300	164,861
Other non-current liabilities	53,057	37,536
Stockholders' equity	1,396,974	1,326,419	1,137,951	1,140,113
Total liabilities and stockholders' equity	2,262,064	2,232,119
Consolidation, Eliminations [Member]
Assets
Other current assets	27,433	18,453
Intercompany receivable (payable)	46,245	49,159
Investments in subsidiaries	(1,317,969)	(1,195,076)
Other non-current assets	(88,137)	(84,044)
Total assets	(1,332,428)	(1,211,508)
Liabilities and Stockholders' Equity
Current liabilities	(72)
Non-current deferred tax liability	(14,387)	(16,430)
Stockholders' equity	(1,317,969)	(1,195,078)
Total liabilities and stockholders' equity	(1,332,428)	(1,211,508)
Consolidated [Member]
Assets
Cash and cash equivalents	209,665	212,175	190,984	266,463
Other current assets	106,694	131,460
Properties, plants, and equipment - net	1,831,564	1,791,601
Other non-current assets	114,141	96,883
Total assets	2,262,064	2,232,119
Liabilities and Stockholders' Equity
Current liabilities	90,985	151,479
Long-term debt	512,129	505,058
Non-current portion of accrued reclamation	55,619	46,766
Non-current deferred tax liability	153,300	164,861
Other non-current liabilities	53,057	37,536
Stockholders' equity	1,396,974	1,326,419
Total liabilities and stockholders' equity	2,262,064	2,232,119
Parent Company [Member]
Assets
Cash and cash equivalents	146,885	126,271	132,266	97,850
Other current assets	7,115	4,795
Properties, plants, and equipment - net	1,572	803
Intercompany receivable (payable)	470,306	528,290
Investments in subsidiaries	1,317,969	1,195,076
Other non-current assets	8,644	5,249
Total assets	1,952,491	1,860,484
Liabilities and Stockholders' Equity
Current liabilities	14,143	10,058
Long-term debt	498,479	490,726
Other non-current liabilities	42,895	33,281
Stockholders' equity	1,396,974	1,326,419
Total liabilities and stockholders' equity	1,952,491	1,860,484
Guarantor Subsidiaries [Member]
Assets
Cash and cash equivalents	33,824	40,009	57,075	168,433
Other current assets	48,981	75,083
Properties, plants, and equipment - net	1,079,658	1,052,102
Intercompany receivable (payable)	(123,671)	(112,815)
Other non-current assets	189,014	164,563
Total assets	1,227,806	1,218,942
Liabilities and Stockholders' Equity
Current liabilities	54,918	117,421
Long-term debt	10,597	14,292
Non-current portion of accrued reclamation	43,314	38,426
Non-current deferred tax liability	14,387	16,430
Other non-current liabilities	11,126	4,043
Stockholders' equity	1,093,464	1,028,330
Total liabilities and stockholders' equity	1,227,806	1,218,942
Non-Guarantor Subsidiaries [Member]
Assets
Cash and cash equivalents	28,956	45,895	1,643	180
Other current assets	23,165	33,129
Properties, plants, and equipment - net	750,334	738,696
Intercompany receivable (payable)	(392,880)	(464,634)
Other non-current assets	4,620	11,115
Total assets	414,195	364,201
Liabilities and Stockholders' Equity
Current liabilities	21,996	24,000
Long-term debt	3,053	40
Non-current portion of accrued reclamation	12,305	8,340
Non-current deferred tax liability	153,300	164,861
Other non-current liabilities	(964)	212
Stockholders' equity	224,505	166,748
Total liabilities and stockholders' equity	$ 414,195	$ 364,201