Quarterly report pursuant to Section 13 or 15(d)

Summary of Significant Accounting Policies - Goodwill (Detail)

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Summary of Significant Accounting Policies - Goodwill (Detail)
 3 Months Ended 6 Months Ended 12 Months Ended
Dec. 31, 2017
USD ($)
Reporting_Unit
Jun. 30, 2018
USD ($)
division
Dec. 31, 2017
USD ($)
Reporting_Unit
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  
Decrease in fair value of reporting units considered for impairment calculation 10.00%   10.00%
Goodwill $ 1,868,600,000 1,897,664,000 $ 1,868,600,000
Intangible assets 263,179,000 261,820,000 263,179,000
Oil and Gas Infrastructure Services Division      
Goodwill And Intangible Assets [Line Items]      
Goodwill $ 596,073,000 590,677,000 $ 596,073,000
Oil and Gas Infrastructure Division, Operating Units that have been Negatively Impacted by Various Factors      
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   48,900,000  
Intangible assets   $ 13,100,000