Note 14 - Guarantor Subsidiaries (Details) - Condensed Consolidating Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014	Jun. 30, 2014	Dec. 31, 2013
Assets
Cash and cash equivalents	$ 191,574	$ 209,665	$ 222,083	$ 212,175
Other current assets	14,040	12,312
Properties, plants, and equipment - net	1,863,440	1,831,564
Other non-current assets	3,576	9,415
Total assets	2,292,268	2,262,064
Liabilities and Stockholders' Equity
Current liabilities	109,193	90,985
Long-term debt	501,376	498,479
Non-current deferred tax liability	137,716	153,300
Other non-current liabilities	51,504	53,057
Stockholders' equity	1,411,574	1,396,974
Total liabilities and stockholders' equity	2,292,268	2,262,064
Consolidation, Eliminations [Member]
Assets
Other current assets	18,441	27,433
Intercompany receivable (payable)	49,609	46,245
Investments in subsidiaries	(1,367,122)	(1,317,969)
Other non-current assets	(74,400)	(88,137)
Total assets	(1,373,472)	(1,332,428)
Liabilities and Stockholders' Equity
Current liabilities	(53)	(72)
Non-current deferred tax liability	(6,297)	(14,387)
Stockholders' equity	(1,367,122)	(1,317,969)
Total liabilities and stockholders' equity	(1,373,472)	(1,332,428)
Consolidated [Member]
Assets
Cash and cash equivalents	191,574	209,665	222,083	212,175
Other current assets	107,510	106,694
Properties, plants, and equipment - net	1,863,440	1,831,564
Other non-current assets	129,744	114,141
Total assets	2,292,268	2,262,064
Liabilities and Stockholders' Equity
Current liabilities	109,193	90,985
Long-term debt	511,563	512,129
Non-current portion of accrued reclamation	70,718	55,619
Non-current deferred tax liability	137,716	153,300
Other non-current liabilities	51,504	53,057
Stockholders' equity	1,411,574	1,396,974
Total liabilities and stockholders' equity	2,292,268	2,262,064
Parent Company [Member]
Assets
Cash and cash equivalents	127,412	146,885	160,374	126,271
Other current assets	4,098	7,115
Properties, plants, and equipment - net	1,686	1,572
Intercompany receivable (payable)	460,184	470,306
Investments in subsidiaries	1,367,122	1,317,969
Other non-current assets	2,975	8,644
Total assets	1,963,477	1,952,491
Liabilities and Stockholders' Equity
Current liabilities	12,179	14,143
Long-term debt	499,104	498,479
Other non-current liabilities	40,620	42,895
Stockholders' equity	1,411,574	1,396,974
Total liabilities and stockholders' equity	1,963,477	1,952,491
Guarantor Subsidiaries [Member]
Assets
Cash and cash equivalents	55,906	33,824	38,639	40,009
Other current assets	47,343	48,981
Properties, plants, and equipment - net	1,115,038	1,079,658
Intercompany receivable (payable)	(130,949)	(123,671)
Other non-current assets	198,256	189,014
Total assets	1,285,594	1,227,806
Liabilities and Stockholders' Equity
Current liabilities	76,371	54,918
Long-term debt	11,190	10,597
Non-current portion of accrued reclamation	42,326	43,314
Non-current deferred tax liability	6,296	14,387
Other non-current liabilities	10,847	11,126
Stockholders' equity	1,138,564	1,093,464
Total liabilities and stockholders' equity	1,285,594	1,227,806
Non-Guarantor Subsidiaries [Member]
Assets
Cash and cash equivalents	8,256	28,956	$ 23,070	$ 45,895
Other current assets	37,628	23,165
Properties, plants, and equipment - net	746,716	750,334
Intercompany receivable (payable)	(378,844)	(392,880)
Other non-current assets	2,913	4,620
Total assets	416,669	414,195
Liabilities and Stockholders' Equity
Current liabilities	20,696	21,996
Long-term debt	1,269	3,053
Non-current portion of accrued reclamation	28,392	12,305
Non-current deferred tax liability	137,717	153,300
Other non-current liabilities	37	(964)
Stockholders' equity	228,558	224,505
Total liabilities and stockholders' equity	$ 416,669	$ 414,195