Note 4 - Revenue From Contracts With Customers - Changes in Estimates (Details) - USD ($)	3 Months Ended	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2018
Increase in revenue from net changes in transaction prices	$ 34,000	$ 75,000
(Decrease) in revenue from net changes in input cost estimates	(479,000)	(570,000)
Net (decrease) in revenue from net changes in estimates	$ (445,000)	$ (495,000)
Number of projects	15	10
Net change in estimate as a percentage of aggregate revenue for associated projects	(9.20%)	(8.80%)