Note 2 - Revision of Previously Issued Financial Statements - Impact of Overstatement of DDA (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended	9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Jun. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Jun. 30, 2018
Credit - Deferred tax liability	$ 164,928					$ 164,928		$ 124,352
Credit - Accumulated deficit	(223,280)					(223,280)		(218,089)
Debit - DDA expense				$ 31,073	$ 59,855	108,814	$ 91,255	126,467	$ 124,918
Income Tax Expense (Benefit), Total	(2,679)	$ (5,130)	$ 16,366	(28,800)	(12,434)	(1,484)	(17,564)	20,963	28,090
Net Income (Loss) Attributable to Parent, Total	$ (23,184)	314	(24,948)	25,082	134	(2,870)	447	(28,520)	61,569
Restatement Adjustment [Member]
Credit - Deferred tax liability								2,806
Credit - Accumulated deficit								(22,605)
Debit - DDA expense				1,483	2,947		3,621	4,537	7,505
Income Tax Expense (Benefit), Total		271	271	271	542		813	1,084	662
Net Income (Loss) Attributable to Parent, Total		$ (1,098)	$ (932)	$ (1,752)	$ (2,684)		$ (3,783)	$ (5,001)	$ (7,978)
Overstatement of Accumulated Depreciation, Depletion and Amortization [Member]
Debit - DDA expense						(3,700)
Income Tax Expense (Benefit), Total						1,000
Net Income (Loss) Attributable to Parent, Total						$ 2,700
Overstatement of Accumulated Depreciation, Depletion and Amortization [Member] | Restatement Adjustment [Member]
Debit - Accumulated DDA (recorded within properties, plants, equipment and mineral interests, net)										$ 14,200
Credit - Deferred tax liability										(3,800)
Credit - Accumulated deficit										$ (7,700)