Note 16 - Guarantor Subsidiaries - Unaudited Interim Condensed Consolidating Balance Sheets (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Cash and cash equivalents	$ 169,777	$ 155,209	$ 209,665	$ 212,175
Other current assets	12,125	9,453
Long-lived assets	2,032,685	1,896,811
Intercompany receivable (payable)
Investments in subsidiaries
Other non-current assets	4,884	2,783
Total assets	2,371,677	2,221,925	2,262,064
Current liabilities	127,480	127,084
Long-term debt	500,979	500,199
Non-current portion of accrued reclamation	79,927	74,549
Non-current deferred tax liability	121,600	119,623
Other non-current liabilities	11,518	52,703
Stockholders' equity	1,479,844	1,338,926	1,396,974	1,326,419
Total liabilities and stockholders' equity	2,371,677	2,221,925
Assets
Cash and cash equivalents	169,777	155,209	209,665	212,175
Other current assets	12,125	9,453
Long-lived assets	2,032,685	1,896,811
Intercompany receivable (payable)
Investments in subsidiaries
Other non-current assets	4,884	2,783
Total assets	2,371,677	2,221,925	2,262,064
Liabilities and Stockholders' Equity
Current liabilities	127,480	127,084
Long-term debt	500,979	500,199
Non-current portion of accrued reclamation	79,927	74,549
Non-current deferred tax liability	121,600	119,623
Other non-current liabilities	11,518	52,703
Stockholders' equity	1,479,844	1,338,926	1,396,974	1,326,419
Total liabilities and stockholders' equity	2,371,677	2,221,925
Consolidation, Eliminations [Member]
Cash and cash equivalents
Other current assets	(1,236)	7,626
Long-lived assets
Intercompany receivable (payable)	124,769	93,179
Investments in subsidiaries	(1,496,787)	(1,252,191)
Other non-current assets	(160,916)	(113,480)
Total assets	(1,533,970)	(1,264,866)
Current liabilities	(22,999)	(9,198)
Long-term debt
Non-current portion of accrued reclamation
Non-current deferred tax liability	(14,212)	(3,477)
Other non-current liabilities	28
Stockholders' equity	(1,496,787)	(1,252,191)
Total liabilities and stockholders' equity	(1,533,970)	(1,264,866)
Assets
Cash and cash equivalents
Other current assets	(1,236)	7,626
Long-lived assets
Intercompany receivable (payable)	124,769	93,179
Investments in subsidiaries	(1,496,787)	(1,252,191)
Other non-current assets	(160,916)	(113,480)
Total assets	(1,533,970)	(1,264,866)
Liabilities and Stockholders' Equity
Current liabilities	(22,999)	(9,198)
Long-term debt
Non-current portion of accrued reclamation
Non-current deferred tax liability	(14,212)	(3,477)
Other non-current liabilities	28
Stockholders' equity	(1,496,787)	(1,252,191)
Total liabilities and stockholders' equity	(1,533,970)	(1,264,866)
Parent Company [Member] | Reportable Legal Entities [Member]
Cash and cash equivalents	113,275	94,167	146,885	126,271
Other current assets	33,950	15,972
Long-lived assets	2,103	2,281
Intercompany receivable (payable)	404,121	540,665
Investments in subsidiaries	1,496,787	1,252,191
Other non-current assets	4,186	2,200
Total assets	2,054,422	1,907,476
Current liabilities	22,401	21,087
Long-term debt	500,979	499,729
Non-current portion of accrued reclamation
Non-current deferred tax liability
Other non-current liabilities	51,198	47,734
Stockholders' equity	1,479,844	1,338,926
Total liabilities and stockholders' equity	2,054,422	1,907,476
Assets
Cash and cash equivalents	113,275	94,167	146,885	126,271
Other current assets	33,950	15,972
Long-lived assets	2,103	2,281
Intercompany receivable (payable)	404,121	540,665
Investments in subsidiaries	1,496,787	1,252,191
Other non-current assets	4,186	2,200
Total assets	2,054,422	1,907,476
Liabilities and Stockholders' Equity
Current liabilities	22,401	21,087
Long-term debt	500,979	499,729
Non-current portion of accrued reclamation
Non-current deferred tax liability
Other non-current liabilities	51,198	47,734
Stockholders' equity	1,479,844	1,338,926
Total liabilities and stockholders' equity	2,054,422	1,907,476
Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Cash and cash equivalents	24,388	42,692	33,824	40,009
Other current assets	65,369	58,453
Long-lived assets	1,258,890	1,147,770
Intercompany receivable (payable)	(222,072)	(301,291)
Investments in subsidiaries
Other non-current assets	186,988	165,080
Total assets	1,313,563	1,112,704
Current liabilities	86,730	84,559
Long-term debt	3,065	6,128
Non-current portion of accrued reclamation	63,025	45,494
Non-current deferred tax liability	14,212	3,264
Other non-current liabilities	5,108	5,834
Stockholders' equity	1,141,423	967,425
Total liabilities and stockholders' equity	1,313,563	1,112,704
Assets
Cash and cash equivalents	24,388	42,692	33,824	40,009
Other current assets	65,369	58,453
Long-lived assets	1,258,890	1,147,770
Intercompany receivable (payable)	(222,072)	(301,291)
Investments in subsidiaries
Other non-current assets	186,988	165,080
Total assets	1,313,563	1,112,704
Liabilities and Stockholders' Equity
Current liabilities	86,730	84,559
Long-term debt	3,065	6,128
Non-current portion of accrued reclamation	63,025	45,494
Non-current deferred tax liability	14,212	3,264
Other non-current liabilities	5,108	5,834
Stockholders' equity	1,141,423	967,425
Total liabilities and stockholders' equity	1,313,563	1,112,704
Non-Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Cash and cash equivalents	32,114	18,350	28,956	45,895
Other current assets	35,524	32,273
Long-lived assets	771,692	746,760
Intercompany receivable (payable)	(307,018)	(332,553)
Investments in subsidiaries
Other non-current assets	5,350	1,781
Total assets	537,662	466,611
Current liabilities	41,348	30,636
Long-term debt	2,773	3,183
Non-current portion of accrued reclamation	16,902	29,055
Non-current deferred tax liability	121,600	119,836
Other non-current liabilities	(325)	(865)
Stockholders' equity	355,364	284,766
Total liabilities and stockholders' equity	537,662	466,611
Assets
Cash and cash equivalents	32,114	18,350	$ 28,956	$ 45,895
Other current assets	35,524	32,273
Long-lived assets	771,692	746,760
Intercompany receivable (payable)	(307,018)	(332,553)
Investments in subsidiaries
Other non-current assets	5,350	1,781
Total assets	537,662	466,611
Liabilities and Stockholders' Equity
Current liabilities	41,348	30,636
Long-term debt	2,773	3,183
Non-current portion of accrued reclamation	16,902	29,055
Non-current deferred tax liability	121,600	119,836
Other non-current liabilities	(325)	(865)
Stockholders' equity	355,364	284,766
Total liabilities and stockholders' equity	$ 537,662	$ 466,611