Note 5 - Revenue Streams and Concentrations (Details Textual) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Mar. 31, 2018	Sep. 30, 2018	Sep. 30, 2017	Jun. 30, 2018	Jan. 01, 2018
Revenue, Remaining Performance Obligation, Amount	$ 8.0		$ 8.0
Contract with Customer, Liability, Total					$ 3.9	$ 4.1
Contract with Customer, Liability, Revenue Recognized	1.4	$ 1.5
Customer Concentration Risk [Member] | Sales Revenue, Net [Member] | National Exchange Carrier Association [Member]
Concentration Risk, Percentage			22.60%	21.80%
Short-term Contract with Customer [Member]
Revenue, Remaining Performance Obligation, Amount	0.9		$ 0.9
Long-term Contract with Customer [Member]
Revenue, Remaining Performance Obligation, Amount	$ 7.1		$ 7.1
Long-term Contract with Customer [Member] | Minimum [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	2 years		2 years
Long-term Contract with Customer [Member] | Maximum [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	5 years		5 years