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