Note 2 - Revenue Recognition - Revenue Accounted for In Accordance With ASC 606, By Timing of Revenue Recognition (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018
Total revenue		$ 49,042	$ 47,758
Transferred over Time [Member]
Total revenue		43,046	40,629
Transferred at Point in Time [Member]
Total revenue		880	922
Regulatory Revenue, Access [Member]
Total revenue	[1]	$ 5,116	$ 6,207

[1] Includes customer ordered service and special access.