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Commitments and Contingencies - Concentrations of Credit Risk (Detail) - Customer Concentration Risk - Customer | 3 Months Ended | 6 Months Ended | 12 Months Ended
--- | --- | --- | ---
Jun. 30, 2017 | Jun. 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 | 1 | 1
Concentration risk percentage |  | 13.00% | 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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- Definition For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 275 -SubTopic 10 -Section 50 -Paragraph 18 -URI http://asc.fasb.org/extlink&oid=64851502&loc=d3e6351-108592 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 20 -URI http://asc.fasb.org/extlink&oid=73719730&loc=d3e13531-108611 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 275 -SubTopic 10 -Section 50 -Paragraph 20 -URI http://asc.fasb.org/extlink&oid=64851502&loc=d3e6404-108592 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 21 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=73719730&loc=d3e13537-108611 + Details
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