Note 2 - Revenue Recognition - 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, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Total revenue		$ 49,228	$ 51,382	$ 97,973	$ 99,140
Transferred over Time [Member]
Total revenue		43,301	43,870	86,050	84,499
Transferred at Point in Time [Member]
Total revenue		1,008	1,460	1,888	2,382
Regulatory Revenue, Access [Member]
Total revenue	[1]	$ 4,919	$ 6,052	$ 10,035	$ 12,259

[1] Includes customer ordered service and special access.