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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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