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Note 16 - Revenue 1 (Details Textual) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2019 USD ($) | Dec. 31, 2018 USD ($) | Dec. 31, 2017 USD ($)
Increase (Decrease) in Revenue from Contract with Customers, Including Assessed Tax | $ 1.2 | $ 0.2 | $ 0.2
Contract with Customer, Liability, Revenue Recognized | 3.7 | 2.6 | $ 1.9
Revenue, Remaining Performance Obligation, Amount | $ 199.0 |  |
Ameron Water Transmission Group, LLC [Member] |  |  |
Contract with Customer, Asset, Increase (Decrease) for Contract Acquired in Business Combination |  | 12.0 |
Contract with Customer, Liability, Increase (Decrease) for Contract Acquired in Business Combination |  | $ 0.1 |
Revenue Benchmark [Member] | Customer Concentration Risk [Member] |  |  |
Number of Major Customers | 1 | 0 | 0
Concentration Risk, Percentage | 23.00% |  |
Accounting Standards Update 2014-09 [Member] |  |  |
Cumulative Effect on Retained Earnings, Net of Tax, Total |  | $ 0.9 |

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