Note 2 - Basis of Presentation (Details Textual) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Cash and Cash Equivalents, Period Increase (Decrease), Total	$ 42,216	$ (566,139)
Cash and Cash Equivalents, at Carrying Value, Ending Balance	$ 582,017	618,945	$ 539,801	$ 1,185,084
Previously Reported [Member]
Net Cash Provided by (Used in) Investing Activities, Continuing Operations, Total		159,100
Cash and Cash Equivalents, Period Increase (Decrease), Total		(50,100)
Cash and Cash Equivalents, at Carrying Value, Ending Balance		$ 167,900		$ 218,000