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Commitments and Contingencies - Concentrations of Credit Risk (Detail) - Customer Concentration Risk - Customer | 3 Months Ended | 9 Months Ended | 12 Months Ended
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Sep. 30, 2017 | Sep. 30, 2017 | Dec. 31, 2016
Electric Power Infrastructure Services Segment Customer One | Net Receivable Position | Electric Power Infrastructure Services Segment |  |  |
Concentration Risk [Line Items] |  |  |
Number of customers representing ten percent or more of concentration risk |  |  | 1
Concentration risk percentage |  |  | 16.00%
Oil and Gas Infrastructure Services Segment Customer One | Net Receivable Position | Oil and Gas Infrastructure Services Segment |  |  |
Concentration Risk [Line Items] |  |  |
Number of customers representing ten percent or more of concentration risk | 1 | 1 |
Concentration risk percentage |  | 10.00% |
Oil and Gas Infrastructure Services Segment Customer One | Sales Revenue, Net | Oil and Gas Infrastructure Services Segment |  |  |
Concentration Risk [Line Items] |  |  |
Concentration risk percentage | 10.00% | 10.00% |

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