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Summary of Significant Accounting Policies - Goodwill (Detail)
 3 Months Ended 12 Months Ended
Mar. 31, 2018
USD ($)
division
Dec. 31, 2017
USD ($)
Reporting_Unit
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  
Decrease in fair value of reporting units considered for impairment calculation   10.00% 10.00%
Goodwill $ 1,902,871,000 $ 1,868,600,000 $ 1,868,600,000
Intangible assets 270,826,000 263,179,000 263,179,000
Non-cash charge for impairment of goodwill 0 57,000,000  
Oil and Gas Infrastructure Services Division      
Goodwill And Intangible Assets [Line Items]      
Goodwill 593,334,000 $ 596,073,000 $ 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 49,400,000    
Intangible assets $ 13,900,000