Note 4 - Revenue From Contracts With Customers - Changes in Estimates (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
(Decrease) increase in revenue from net changes in transaction prices	$ (3,000)	$ 71,000	$ 1,000	$ 146,000
Increase (decrease) in revenue from net changes in input cost estimates	334,000	(1,170,000)	(224,000)	(1,740,000)
Net increase (decrease) in revenue from net Changes in estimates	$ 331,000	$ (1,099,000)	$ (223,000)	$ (1,594,000)
Number of projects	27	15	18	15
Net change in estimate as a percentage of aggregate revenue for associated projects	3.80%	(2.40%)	(3.60%)	(3.40%)