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Note 2 - Summary of Significant Accounting Policies (Details Textual)	3 Months Ended	12 Months Ended
	Dec. 31, 2017 USD ($)	Dec. 31, 2017 USD ($) shares	Dec. 31, 2016 USD ($) shares	Dec. 31, 2015 USD ($) shares	Dec. 31, 2018 USD ($)	Mar. 31, 2015 USD ($)
Investments	$ 0	$ 0	$ 0
Book Overdrafts	0	0	0
Workers' Compensation Liability	3,700,000	3,700,000	3,400,000
Workers' Compensation Liability, Current	422,000	$ 422,000	$ 569,000
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount | shares		196,000	198,000	179,000
Number of Customers with Receivable Balance in Excess of Ten Percent of Receivables		2	2
Income Tax Expense (Benefit)		$ (1,100,000)	$ (4,098,000)	$ (8,523,000)
Accounting Standards Update 2016-09 [Member]
Income Tax Expense (Benefit)		$ 800,000
Accounting Standards Update 2014-09 [Member] | Retained Earnings [Member] | Scenario, Forecast [Member]
Cumulative Effect of New Accounting Principle in Period of Adoption					$ 1,000,000
Sales Revenue, Net [Member] | Customer Concentration Risk [Member]
Number of Major Customers		0	1	2
Sales Revenue, Net [Member] | Customer Concentration Risk [Member] | Customer One [Member]
Concentration Risk, Percentage			28.00%	16.00%
Sales Revenue, Net [Member] | Customer Concentration Risk [Member] | Customer Two [Member]
Concentration Risk, Percentage				13.00%
Accrued Liability [Member]
Workers' Compensation Liability, Current	400,000	$ 400,000	$ 600,000
Other Long-term Liabilities [Member]
Workers' Compensation Liability, Noncurrent	3,300,000	3,300,000	2,800,000
Cost of Sales [Member]
Workers Compensation Expense	$ 1,200,000
Cost of Sales [Member] | Accounting Standards Update 2017-07 [Member] | Year Ended December 31, 2016 [Member]
Prior Period Reclassification Adjustment		$ 0	$ 400,000
Water Transmission Group [Member]
Goodwill						$ 5,300,000
Minimum [Member]
Finite-Lived Intangible Asset, Useful Life		4 years
Maximum [Member]
Finite-Lived Intangible Asset, Useful Life		15 years
Land Improvements [Member] | Minimum [Member]
Property, Plant and Equipment, Useful Life		15 years
Land Improvements [Member] | Maximum [Member]
Property, Plant and Equipment, Useful Life		30 years
Building [Member] | Minimum [Member]
Property, Plant and Equipment, Useful Life		20 years
Building [Member] | Maximum [Member]
Property, Plant and Equipment, Useful Life		40 years
Machinery and Equipment [Member] | Minimum [Member]
Property, Plant and Equipment, Useful Life		3 years
Machinery and Equipment [Member] | Maximum [Member]
Property, Plant and Equipment, Useful Life		30 years

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