Note 14 - Guarantor Subsidiaries (Details) - Condensed Consolidating Balance Sheets (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2013	Dec. 31, 2012
Assets
Cash and cash equivalents	$ 207,642	$ 212,175	$ 168,614	$ 190,984
Other current assets	13,016	8,324
Properties, plants, and equipment - net	1,805,632	1,791,601
Other non-current assets	9,269	5,867
Total assets	2,250,281	2,232,119
Liabilities and Stockholders' Equity
Current liabilities	151,560	151,479
Long-term debt	491,042	490,726
Non-current deferred tax liability	159,890	164,861
Other non-current liabilities	34,862	37,536
Stockholders' equity	1,343,462	1,326,419
Total liabilities and stockholders' equity	2,250,281	2,232,119
Consolidation, Eliminations [Member]
Assets
Other current assets	(5,290)	18,453
Intercompany receivable (payable)	56,869	49,159
Investments in subsidiaries	(1,235,581)	(1,176,293)
Other non-current assets	(77,583)	(84,043)
Total assets	(1,261,585)	(1,192,724)
Liabilities and Stockholders' Equity
Current liabilities	(13,673)
Non-current deferred tax liability	(12,331)	(16,431)
Stockholders' equity	(1,235,581)	(1,176,293)
Total liabilities and stockholders' equity	(1,261,585)	(1,192,724)
Consolidated [Member]
Assets
Cash and cash equivalents	207,642	212,175
Other current assets	124,629	131,460
Properties, plants, and equipment - net	1,805,632	1,791,601
Other non-current assets	112,378	96,883
Total assets	2,250,281	2,232,119
Liabilities and Stockholders' Equity
Current liabilities	151,560	151,479
Long-term debt	505,154	505,058
Non-current portion of accrued reclamation	55,353	46,766
Non-current deferred tax liability	159,890	164,861
Other non-current liabilities	34,862	37,536
Stockholders' equity	1,343,462	1,326,419
Total liabilities and stockholders' equity	2,250,281	2,232,119
Parent Company [Member]
Assets
Cash and cash equivalents	137,252	126,271
Other current assets	9,706	4,795
Properties, plants, and equipment - net	1,069	803
Intercompany receivable (payable)	508,911	547,074
Investments in subsidiaries	1,235,581	1,176,293
Other non-current assets	8,742	5,248
Total assets	1,901,261	1,860,484
Liabilities and Stockholders' Equity
Current liabilities	35,021	10,058
Long-term debt	491,043	490,726
Other non-current liabilities	31,735	33,281
Stockholders' equity	1,343,462	1,326,419
Total liabilities and stockholders' equity	1,901,261	1,860,484
Guarantor Subsidiaries [Member]
Assets
Cash and cash equivalents	43,399	40,009
Other current assets	78,346	75,083
Properties, plants, and equipment - net	1,061,211	1,052,102
Intercompany receivable (payable)	(111,937)	(131,599)
Other non-current assets	166,027	164,563
Total assets	1,237,046	1,200,158
Liabilities and Stockholders' Equity
Current liabilities	109,246	117,421
Long-term debt	14,077	14,292
Non-current portion of accrued reclamation	47,061	38,426
Non-current deferred tax liability	12,331	16,431
Other non-current liabilities	4,216	4,043
Stockholders' equity	1,050,115	1,009,545
Total liabilities and stockholders' equity	1,237,046	1,200,158
Non-Guarantor Subsidiaries [Member]
Assets
Cash and cash equivalents	26,991	45,895
Other current assets	41,867	33,129
Properties, plants, and equipment - net	743,352	738,696
Intercompany receivable (payable)	(453,843)	(464,634)
Other non-current assets	15,192	11,115
Total assets	373,559	364,201
Liabilities and Stockholders' Equity
Current liabilities	20,966	24,000
Long-term debt	34	40
Non-current portion of accrued reclamation	8,292	8,340
Non-current deferred tax liability	159,890	164,861
Other non-current liabilities	(1,089)	212
Stockholders' equity	185,466	166,748
Total liabilities and stockholders' equity	$ 373,559	$ 364,201