Note 14 - Guarantor Subsidiaries - Unaudited Interim Condensed Consolidating Balance Sheets (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015	Dec. 31, 2014
Parent Company [Member]
Assets
Cash and cash equivalents	$ 109,756	$ 94,167	$ 123,585	$ 146,885
Other current assets	51,486	15,972
Properties, plants, and equipment - net	2,226	2,281
Intercompany receivable (payable)	477,706	540,665
Investments in subsidiaries	1,359,813	1,252,191
Other non-current assets	1,896	2,200
Total assets	2,002,883	1,907,476
Liabilities and Stockholders' Equity
Current liabilities	(6,626)	21,087
Long-term debt	500,666	499,729
Non-current portion of accrued reclamation
Non-current deferred tax liability
Other non-current liabilities	46,860	47,734
Shareholders' equity	1,461,983	1,338,926
Total liabilities and stockholders' equity	2,002,883	1,907,476
Guarantor Subsidiaries [Member]
Assets
Cash and cash equivalents	39,255	42,692	45,082	33,824
Other current assets	58,839	58,453
Properties, plants, and equipment - net	1,255,019	1,147,770
Intercompany receivable (payable)	(322,988)	(301,291)
Investments in subsidiaries
Other non-current assets	190,705	165,080
Total assets	1,220,830	1,112,704
Liabilities and Stockholders' Equity
Current liabilities	84,493	84,559
Long-term debt	4,019	6,128
Non-current portion of accrued reclamation	55,512	45,494
Non-current deferred tax liability	15,258	3,264
Other non-current liabilities	4,856	5,834
Shareholders' equity	1,056,692	967,425
Total liabilities and stockholders' equity	1,220,830	1,112,704
Non-Guarantor Subsidiaries [Member]
Assets
Cash and cash equivalents	18,833	18,350	5,787	28,956
Other current assets	46,082	32,273
Properties, plants, and equipment - net	765,864	746,760
Intercompany receivable (payable)	(325,799)	(332,553)
Investments in subsidiaries
Other non-current assets	8,245	1,781
Total assets	513,225	466,611
Liabilities and Stockholders' Equity
Current liabilities	57,908	30,636
Long-term debt	2,513	3,183
Non-current portion of accrued reclamation	28,086	29,055
Non-current deferred tax liability	121,973	119,836
Other non-current liabilities	(376)	(865)
Shareholders' equity	303,121	284,766
Total liabilities and stockholders' equity	513,225	466,611
Consolidated Entities [Member]
Assets
Cash and cash equivalents	167,844	155,209	174,454	209,665
Other current assets	142,157	114,324
Properties, plants, and equipment - net	2,023,109	1,896,811
Intercompany receivable (payable)
Investments in subsidiaries
Other non-current assets	30,569	55,581
Total assets	2,363,679	2,221,925
Liabilities and Stockholders' Equity
Current liabilities	135,147	127,084
Long-term debt	507,198	509,040
Non-current portion of accrued reclamation	83,598	74,549
Non-current deferred tax liability	124,385	119,623
Other non-current liabilities	51,368	52,703
Shareholders' equity	1,461,983	1,338,926
Total liabilities and stockholders' equity	2,363,679	2,221,925
Consolidation, Eliminations [Member]
Assets
Cash and cash equivalents
Other current assets	(14,250)	7,626
Properties, plants, and equipment - net
Intercompany receivable (payable)	171,081	93,179
Investments in subsidiaries	(1,359,813)	(1,252,191)
Other non-current assets	(170,277)	(113,480)
Total assets	(1,373,259)	(1,264,866)
Liabilities and Stockholders' Equity
Current liabilities	(628)	(9,198)
Long-term debt
Non-current portion of accrued reclamation
Non-current deferred tax liability	(12,846)	(3,477)
Other non-current liabilities	28
Shareholders' equity	(1,359,813)	(1,252,191)
Total liabilities and stockholders' equity	(1,373,259)	(1,264,866)
Cash and cash equivalents	167,844	155,209	$ 174,454	$ 209,665
Other current assets	10,451	9,453
Properties, plants, and equipment - net	2,023,109	1,896,811
Other non-current assets	2,573	2,783
Total assets	2,363,679	2,221,925
Current liabilities	135,147	127,084
Long-term debt	500,666	500,199
Non-current deferred tax liability	124,385	119,623
Other non-current liabilities	7,626	6,190
Shareholders' equity	1,461,983	1,338,926
Total liabilities and stockholders' equity	$ 2,363,679	$ 2,221,925