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Revenue - Over Time Sales (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2022 | Dec. 31, 2021
Disaggregation of Revenue |  |
Over time sales, amount | $ 135,910 | $ 153,631
Over time sales, percentage | 27.30% | 29.90%
Over time input method |  |
Disaggregation of Revenue |  |
Over time sales, amount | $ 67,116 | $ 100,787
Over time sales, percentage | 13.50% | 19.60%
Over time output method |  |
Disaggregation of Revenue |  |
Over time sales, amount | $ 68,794 | $ 52,844
Over time sales, percentage | 13.80% | 10.30%

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- Definition Over Time Sales, Amount + References No definition available. + Details
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- Definition Over Time Sales, Percent + References No definition available. + Details
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Namespace Prefix: | fstr_
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Balance Type: | na
Period Type: | duration

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Details
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Period Type: |

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- Details
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Data Type: | na
Balance Type: |
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