Note 5 - Income Taxes - Reconciliation of Statutory Federal Income Tax Rate to Annual Tax Provision (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 21, 2017	Dec. 31, 2016	Dec. 31, 2015
Computed “statutory” benefit (provision), Amount	$ 1,274		$ (33,941)	$ 10,731
Computed “statutory” benefit (provision), Percentage	35.00%	35.00%	35.00%	35.00%
Percentage depletion, Amount	$ 5,174		$ 8,114	$ 2,432
Percentage depletion, Percentage	142.00%		(8.00%)	8.00%
Change in valuation allowance, Amount	$ 24,464		$ 11,336	$ (84,951)
Change in valuation allowance, Percentage	672.00%		(12.00%)	(277.00%)
Federal rate change, Amount	$ (37,546)
Federal rate change, Percentage	(1031.00%)
State taxes, net of federal taxes, Amount	$ 1,112		$ (565)	$ (3,639)
State taxes, net of federal taxes, Percentage	30.00%		1.00%	(12.00%)
Foreign currency remeasurement of monetary assets and liabilities, Amount	$ (10,357)		$ (4,598)	$ 28,184
Foreign currency remeasurement of monetary assets and liabilities, Percentage	(284.00%)		5.00%	92.00%
Rate differential on foreign earnings, Amount	$ (1,438)		$ (6,853)	$ (4,746)
Rate differential on foreign earnings, Percentage	(39.00%)		7.00%	(15.00%)
Compensation, Amount	$ (661)		$ (1,517)	$ (1,014)
Compensation, Percentage	(18.00%)		1.00%	(3.00%)
Foreign withholding taxes, Amount	$ (278)
Foreign withholding taxes, percentage	(8.00%)
Expiration of U.S. foreign tax credits, Amount	$ (2,300)
Expiration of U.S. foreign tax credits, percentage	(63.00%)
Other, Amount	$ 677		$ 596	$ (3,307)
Other, Percentage	18.00%		(1.00%)	(12.00%)
Total income tax provision	$ (19,879)		$ (27,428)	$ (56,310)
Total provision, Percentage	(546.00%)		28.00%	(184.00%)