Note 3 - Accounts Receivable and Accounts Receivable Allowance - Activity in Allowance for Doubtful Accounts (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Balance--beginning of period	$ 13,683	$ 14,799
Provision	5,411	20,453
Charge-offs	(5,057)	(21,569)
Balance--end of period	$ 14,037	$ 13,683