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Note 15 - Revenue 1 (Details Textual) $ in Thousands | 12 Months Ended |  |
--- | --- | --- | ---
Dec. 31, 2020 USD ($) | Dec. 31, 2019 USD ($) | Dec. 31, 2018 USD ($) | Jan. 01, 2018 USD ($) | Dec. 31, 2017 USD ($)
Stockholders' Equity Attributable to Parent, Ending Balance | $ 269,626 | $ 248,158 | $ 218,590 |  | $ 200,264
Increase (Decrease) in Revenue from Contract with Customers, Including Assessed Tax | 2,200 | (1,200) | (200) |  |
Contract with Customer, Liability, Revenue Recognized | 12,300 | $ 3,700 | 2,600 |  |
Revenue, Remaining Performance Obligation, Amount | $ 167,000 |  |  |  |
Ameron Water Transmission Group, LLC [Member] |  |  |  |  |
Contract with Customer, Asset, Increase (Decrease) for Contract Acquired in Business Combination |  |  | 12,000 |  |
Contract with Customer, Liability, Increase (Decrease) for Contract Acquired in Business Combination |  |  | $ 100 |  |
Revenue Benchmark [Member] | Customer Concentration Risk [Member] |  |  |  |  |
Number of Major Customers | 1 | 1 | 0 |  |
Concentration Risk, Percentage | 16.00% | 23.00% |  |  |
Retained Earnings [Member] |  |  |  |  |
Stockholders' Equity Attributable to Parent, Ending Balance | $ 148,381 | $ 129,331 | $ 101,194 |  | 81,757
Accounting Standards Update 2014-09 [Member] | Cumulative Effect, Period of Adoption, Adjustment [Member] |  |  |  |  |
Stockholders' Equity Attributable to Parent, Ending Balance |  |  |  |  | (875)
Accounting Standards Update 2014-09 [Member] | Cumulative Effect, Period of Adoption, Adjustment [Member] | Retained Earnings [Member] |  |  |  |  |
Stockholders' Equity Attributable to Parent, Ending Balance |  |  |  | $ (900) | $ (875)

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