Note 4 - Accounts Receivable and Accounts Receivable Allowance - Activity in Allowance for Doubtful Accounts (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Balance--beginning of period	$ 14,799	$ 10,772
Provision	10,332	20,233
Charge-offs	(10,809)	(16,206)
Balance--end of period	$ 14,322	$ 14,799