Note 14 - Guarantor Subsidiaries (Details) - Condensed Consolidating Balance Sheets (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014	Dec. 31, 2013
Assets
Cash and cash equivalents	$ 196,231	$ 209,665	$ 207,642	$ 212,175
Other current assets	15,337	12,312
Properties, plants, and equipment - net	1,837,173	1,831,564
Other non-current assets	10,692	9,415
Total assets	2,259,951	2,262,064	2,262,064
Liabilities and Stockholders' Equity
Current liabilities	88,538	90,985
Long-term debt	498,791	498,479
Non-current deferred tax liability	138,422	153,300
Other non-current liabilities	47,504	53,057
Stockholders' equity	1,419,325	1,396,974
Total liabilities and stockholders' equity	2,259,951	2,262,064
Consolidation, Eliminations [Member]
Assets
Other current assets	13,963	27,433
Intercompany receivable (payable)	56,254	46,245
Investments in subsidiaries	(1,365,864)	(1,317,969)
Other non-current assets	(82,061)	(88,137)
Total assets	(1,377,708)	(1,332,428)
Liabilities and Stockholders' Equity
Current liabilities	(4,808)	(72)
Non-current deferred tax liability	(7,036)	(14,387)
Stockholders' equity	(1,365,864)	(1,317,969)
Total liabilities and stockholders' equity	(1,377,708)	(1,332,428)
Consolidated [Member]
Assets
Cash and cash equivalents	196,231	209,665	207,642	212,175
Other current assets	112,094	106,694
Properties, plants, and equipment - net	1,837,173	1,831,564
Other non-current assets	114,453	114,141
Total assets	2,259,951	2,262,064
Liabilities and Stockholders' Equity
Current liabilities	88,538	90,985
Long-term debt	510,381	512,129
Non-current portion of accrued reclamation	55,781	55,619
Non-current deferred tax liability	138,422	153,300
Other non-current liabilities	47,504	53,057
Stockholders' equity	1,419,325	1,396,974
Total liabilities and stockholders' equity	2,259,951	2,262,064
Parent Company [Member]
Assets
Cash and cash equivalents	145,284	146,885	137,252	126,271
Other current assets	17,969	7,115
Properties, plants, and equipment - net	1,838	1,572
Intercompany receivable (payable)	439,735	470,306
Investments in subsidiaries	1,365,864	1,317,969
Other non-current assets	10,102	8,644
Total assets	1,980,792	1,952,491
Liabilities and Stockholders' Equity
Current liabilities	24,709	14,143
Long-term debt	498,791	498,479
Other non-current liabilities	37,967	42,895
Stockholders' equity	1,419,325	1,396,974
Total liabilities and stockholders' equity	1,980,792	1,952,491
Guarantor Subsidiaries [Member]
Assets
Cash and cash equivalents	35,957	33,824	43,399	40,009
Other current assets	52,393	48,981
Properties, plants, and equipment - net	1,085,971	1,079,658
Intercompany receivable (payable)	(125,964)	(123,671)
Other non-current assets	182,205	189,014
Total assets	1,230,562	1,227,806
Liabilities and Stockholders' Equity
Current liabilities	48,654	54,918
Long-term debt	10,150	10,597
Non-current portion of accrued reclamation	43,886	43,314
Non-current deferred tax liability	7,036	14,387
Other non-current liabilities	10,386	11,126
Stockholders' equity	1,110,450	1,093,464
Total liabilities and stockholders' equity	1,230,562	1,227,806
Non-Guarantor Subsidiaries [Member]
Assets
Cash and cash equivalents	14,990	28,956	26,991	45,895
Other current assets	27,769	23,165
Properties, plants, and equipment - net	749,364	750,334
Intercompany receivable (payable)	(370,025)	(392,880)
Other non-current assets	4,207	4,620
Total assets	426,305	414,195
Liabilities and Stockholders' Equity
Current liabilities	19,983	21,996
Long-term debt	1,440	3,053
Non-current portion of accrued reclamation	11,895	12,305
Non-current deferred tax liability	138,422	153,300
Other non-current liabilities	(849)	(964)
Stockholders' equity	255,414	224,505
Total liabilities and stockholders' equity	$ 426,305	$ 414,195