Note 2 - Basis of Presentation (Details Textual) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Cash and Cash Equivalents, Period Increase (Decrease), Total	$ (135,660)	$ (630,672)
Cash and Cash Equivalents, at Carrying Value, Ending Balance	$ 404,141	554,412	$ 539,801	$ 1,185,084
Previously Reported [Member]
Net Cash Provided by (Used in) Investing Activities, Continuing Operations, Total		135,000
Cash and Cash Equivalents, Period Increase (Decrease), Total		(57,500)
Cash and Cash Equivalents, at Carrying Value, Ending Balance		$ 160,500		$ 218,000