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Note 10 - Revenue 1 (Details Textual) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
	Jul. 27, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Increase (Decrease) in Revenue from Contract with Customers, Including Assessed Tax		$ (0.2)	$ 0.3	$ 0.5	$ (0.3)
Contract with Customer, Liability, Revenue Recognized		0.1	$ 0.9	2.2	$ 1.7
Revenue, Remaining Performance Obligation, Amount		$ 100.2		$ 100.2
Ameron Water Transmission Group, LLC [Member]
Contract with Customer, Asset, Increase (Decrease) for Contract Acquired in Business Combination	$ 11.9
Contract with Customer, Liability, Increase (Decrease) for Contract Acquired in Business Combination	$ 0.1

X

- Definition

The increase (decrease) during the period of the amount, including tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer.

+ References

No definition available.

+ Details

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X

- Definition

Amount of increase (decrease) in right to consideration in exchange for good or service transferred to customer when right is conditioned on something other than passage of time, from business combination.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 10
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130551-203045

+ Details

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X

- Definition

Amount of increase (decrease) in obligation to transfer good or service to customer for which consideration from customer has been received or is due, from business combination.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 10
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130551-203045

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X

- Definition

Amount of revenue recognized that was previously included in balance of obligation to transfer good or service to customer for which consideration from customer has been received or is due.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 8
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130549-203045

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X

- Definition

Amount of transaction price allocated to performance obligation that has not been recognized as revenue.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 13
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130556-203045

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- Details

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Period Type: