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Summary of Significant Accounting Policies - Goodwill (Detail) | 3 Months Ended | 9 Months Ended
--- | --- | ---
Dec. 31, 2017 USD ($) Reporting_Unit | Sep. 30, 2018 USD ($) division
Goodwill And Intangible Assets [Line Items] |  |
Number of internal divisions | division |  | 2
Number of reporting units impacted by impairment charges | Reporting_Unit | 2 |
Non-cash charge for impairment of goodwill | $ 57,000,000.0 | $ 0
Decrease in fair value of reporting units considered for impairment calculation | 10.00% |
Goodwill | $ 1,868,600,000 | 1,912,139,000
Intangible assets | $ 263,179,000 | 284,411,000
Oil and Gas Infrastructure Services Division |  |
Goodwill And Intangible Assets [Line Items] |  |
Number of reporting units with fair values that approximated carrying values after sensitivity of a decrease in fair value | Reporting_Unit | 1 |
Goodwill |  | 49,400,000
Intangible assets |  | $ 12,700,000

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