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Schedule II - Valuation and Qualifying Accounts | 12 Months Ended
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Dec. 31, 2017
Notes to Financial Statements |
Schedule of Valuation and Qualifying Accounts Disclosure [Text Block] | Schedule II NORTHWEST PIPE COMPANY VALUATION AND QUALIFYING ACCOUNTS (Dollars in thousands)
|  | Balance at Beginning of Perio d |  |  | Charged to Profit and Los s |  |  | Deduction from Reserve s |  |  | Balance at End of Perio d |
Year Ended December 31, 2017 : |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Allowance for doubtful account s |  | $ | 515 |  |  | $ | 637 |  |  | $ | (675 | ) |  | $ | 477 |
Valuation allowance for deferred tax asset s |  |  | 8,217 |  |  |  | 2,196 |  |  |  | - |  |  |  | 10,413 |
Year Ended December 31, 2016 : |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Allowance for doubtful account s |  | $ | 751 | (1) |  | $ | 295 |  |  | $ | (531 | ) |  | $ | 515 |
Valuation allowance for deferred tax asset s |  |  | 7,057 |  |  |  | 1,160 |  |  |  | - |  |  |  | 8,217 |
Year Ended December 31, 2015 : |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Allowance for doubtful account s |  | $ | 755 | (1) |  | $ | 416 |  |  | $ | (420 | ) |  | $ | 751 | (1)
Valuation allowance for deferred tax asset s |  |  | 1,858 |  |  |  | 5,217 |  |  |  | (18 | ) |  |  | 7,057 |
( 1 ) Includes amounts that were classified as held for sale.

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- References No definition available. + Details
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- Definition The entire disclosure for any allowance and reserve accounts (their beginning and ending balances, as well as a reconciliation by type of activity during the period). Alternatively, disclosure of the required information may be within the footnotes to the financial statements or a supplemental schedule to the financial statements. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -URI http://asc.fasb.org/topic&trid=2122369 + Details
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