Note 4 - Accounts Receivable - Summary of Accounts Receivable, Net (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accounts receivable, gross	$ 35,264	$ 26,177
Less: allowance for doubtful accounts	(2,729)	(1,115)	$ (1,693)	$ (2,338)
Accounts receivable, net	32,535	25,062
Retail Customers [Member]
Accounts receivable, gross	22,227	17,511
Wholesale Carriers [Member]
Accounts receivable, gross	8,146	4,293
Other [Member]
Accounts receivable, gross	$ 4,891	$ 4,373