Note 2 - Revenue - Revenue Accounted for In Accordance With ASC 606, By Timing of Revenue Recognition (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Total revenue		$ 51,503	$ 49,228	$ 101,727	$ 97,973
Transferred over Time [Member]
Total revenue		45,739	43,301	89,858	86,050
Transferred at Point in Time [Member]
Total revenue		1,192	1,008	2,606	1,888
Regulatory Revenue, Access [Member]
Total revenue	[1]	$ 4,572	$ 4,919	$ 9,263	$ 10,035

[1] Includes customer ordered service and special access.