Note 1 - Description of Business and Summary of Significant Accounting Policies - Trade Revenue and Expense (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net trade (loss) income	$ 165,570	$ 15,316	$ 70,561	$ 10,505	$ 35,834	$ (213)	$ 17,662	$ 8,990	$ 261,952	$ 62,273	$ 39,301
Advertising Barter Transactions [Member]
Trade revenue									1,832	2,069	2,299
Trade expense									(1,863)	(1,997)	(2,188)
Net trade (loss) income									$ (31)	$ 72	$ 111