Note 4 - Revenue From Contracts With Customers - Changes in Estimates (Details) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Increase in revenue from net changes in transaction prices	$ 9,000	$ 15,000
(Decrease) increase in revenue from net changes in input cost estimates	(181,000)	894,000
Net (decrease) increase in revenue from net Changes in estimates	$ (172,000)	$ 909,000
Number of projects	21	10
Net change in estimate as a percentage of aggregate revenue for associated projects	(0.20%)	2.10%