Note 14 - Guarantor Subsidiaries (Details) - Condensed Consolidating Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014	Dec. 31, 2013
Assets
Cash and cash equivalents	$ 174,454	$ 209,665	$ 222,360	$ 212,175
Other current assets	15,957	12,312
Properties, plants, and equipment - net	1,878,177	1,831,564
Other non-current assets	3,034	9,415
Total assets	2,285,213	2,262,064
Liabilities and Shareholders' Equity
Current liabilities	125,616	90,985
Long-term debt	501,281	498,479
Non-current deferred tax liability	125,753	153,300
Other non-current liabilities	50,485	53,057
Stockholders' equity	1,401,771	1,396,974
Total liabilities and stockholders' equity	2,285,213	2,262,064
Consolidation, Eliminations [Member]
Assets
Other current assets	19,573	27,433
Intercompany receivable (payable)	46,082	46,245
Investments in subsidiaries	(1,373,915)	(1,317,969)
Other non-current assets	(72,328)	(88,137)
Total assets	(1,380,588)	(1,332,428)
Liabilities and Shareholders' Equity
Current liabilities	(1,740)	(72)
Non-current deferred tax liability	(4,933)	(14,387)
Stockholders' equity	(1,373,915)	(1,317,969)
Total liabilities and stockholders' equity	(1,380,588)	(1,332,428)
Consolidated [Member]
Assets
Cash and cash equivalents	174,454	209,665	222,360	212,175
Other current assets	116,709	106,694
Properties, plants, and equipment - net	1,878,177	1,831,564
Other non-current assets	115,873	114,141
Total assets	2,285,213	2,262,064
Liabilities and Shareholders' Equity
Current liabilities	125,616	90,985
Long-term debt	510,766	512,129
Non-current portion of accrued reclamation	70,822	55,619
Non-current deferred tax liability	125,753	153,300
Other non-current liabilities	50,485	53,057
Stockholders' equity	1,401,771	1,396,974
Total liabilities and stockholders' equity	2,285,213	2,262,064
Parent Company [Member]
Assets
Cash and cash equivalents	123,585	146,885	151,739	126,271
Other current assets	5,486	7,115
Properties, plants, and equipment - net	1,522	1,572
Intercompany receivable (payable)	459,203	470,306
Investments in subsidiaries	1,373,915	1,317,969
Other non-current assets	2,339	8,644
Total assets	1,966,050	1,952,491
Liabilities and Shareholders' Equity
Current liabilities	21,123	14,143
Long-term debt	499,417	498,479
Other non-current liabilities	43,739	42,895
Stockholders' equity	1,401,771	1,396,974
Total liabilities and stockholders' equity	1,966,050	1,952,491
Guarantor Subsidiaries [Member]
Assets
Cash and cash equivalents	45,082	33,824	48,205	40,009
Other current assets	56,780	48,981
Properties, plants, and equipment - net	1,131,491	1,079,658
Intercompany receivable (payable)	(141,131)	(123,671)
Other non-current assets	183,590	189,014
Total assets	1,275,812	1,227,806
Liabilities and Shareholders' Equity
Current liabilities	84,121	54,918
Long-term debt	10,343	10,597
Non-current portion of accrued reclamation	42,708	43,314
Non-current deferred tax liability	5,211	14,387
Other non-current liabilities	6,765	11,126
Stockholders' equity	1,126,664	1,093,464
Total liabilities and stockholders' equity	1,275,812	1,227,806
Non-Guarantor Subsidiaries [Member]
Assets
Cash and cash equivalents	5,787	28,956	$ 22,416	$ 45,895
Other current assets	34,870	23,165
Properties, plants, and equipment - net	745,164	750,334
Intercompany receivable (payable)	(364,154)	(392,880)
Other non-current assets	2,272	4,620
Total assets	423,939	414,195
Liabilities and Shareholders' Equity
Current liabilities	22,112	21,996
Long-term debt	1,006	3,053
Non-current portion of accrued reclamation	28,114	12,305
Non-current deferred tax liability	125,475	153,300
Other non-current liabilities	(19)	(964)
Stockholders' equity	247,251	224,505
Total liabilities and stockholders' equity	$ 423,939	$ 414,195