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Accounts Receivable (Details) - USD ($) $ in Thousands | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
--- | --- | --- | --- | ---
Receivables [Abstract] |  |  |  |
Trade accounts receivable | $ 133,238 | $ 124,609 |  |
Costs in excess of billings | 20,607 | 22,634 |  |
Total contract receivables | 153,845 | 147,243 |  |
Less allowance for doubtful accounts | (6,330) | (6,960) | $ (6,434) | $ (5,272)
Accounts receivable | $ 147,515 | $ 140,283 |  |

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