Note 4 - Income Taxes - Major Components of Income Tax Provision (Benefit) (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
Domestic						$ 1	$ (12,797)
Foreign	80	(3,959)				4,250	17,491
Total current income tax provision (benefit)	80	(3,959)				4,251	4,694
Domestic	(3,778)	1,980				(3,778)	(13,958)
Foreign	1,019	(3,151)				(1,957)	(8,300)
Total deferred income tax provision (benefit)	(2,759)	(1,171)				(5,735)	(22,258)
Total income tax provision (benefit)	$ (2,679)	$ (5,130)	$ 16,366	$ (28,800)	$ (12,434)	$ (1,484)	$ (17,564)	$ 20,963	$ 28,090