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Summary of Business and Significant Accounting Policies - Narrative (Details) - USD ($) $ in Millions | 3 Months Ended |
--- | --- | ---
Mar. 31, 2018 | Mar. 31, 2017 | Dec. 31, 2017
Costs and estimated earnings in excess of billings |  |  |
Business Acquisition [Line Items] |  |  |
Unapproved change orders, amount | $ 5.0 |  | $ 5.0
Contracts receivable, claims and uncertain amounts | 6.0 |  | 5.0
Contracts receivable, unpaid project contract price | 0.0 |  | $ 0.0
Operating income (Loss) |  |  |
Business Acquisition [Line Items] |  |  |
Estimated construction gain (loss) before tax | $ 1.3 | $ 0.8 |
Minimum |  |  |
Business Acquisition [Line Items] |  |  |
Revenue recognition, contract term | 12 months |  |
Warranty term | 1 year |  |
Maximum |  |  |
Business Acquisition [Line Items] |  |  |
Revenue recognition, contract term | 36 months |  |
Warranty term | 2 years |  |

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