Note 4 - Accounts Receivable - Summary of Accounts Receivable, Net (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accounts receivable, gross	$ 38,981	$ 35,408
Less: allowance for doubtful accounts	(4,627)	(3,936)	$ (2,729)
Accounts receivable, net	34,354	31,472
Retail Customers [Member]
Accounts receivable, gross	22,101	21,732
Wholesale Carriers [Member]
Accounts receivable, gross	13,157	9,315
Other [Member]
Accounts receivable, gross	$ 3,723	$ 4,361