Quarterly report pursuant to Section 13 or 15(d)

Summary of Significant Accounting Policies - Goodwill (Details)

v3.19.1
Summary of Significant Accounting Policies - Goodwill (Details)
$ in Thousands
3 Months Ended
Mar. 31, 2019
USD ($)
division
Dec. 31, 2018
USD ($)
Dec. 31, 2017
USD ($)
Goodwill And Intangible Assets [Line Items]      
Number of internal divisions | division 2    
Decrease in fair value of reporting units considered for impairment calculation 10.00%    
Goodwill $ 1,927,028 $ 1,899,879 $ 1,868,600
Intangible assets 276,070 $ 280,180  
Oil and Gas Infrastructure Services Division      
Goodwill And Intangible Assets [Line Items]      
Goodwill 48,500    
Intangible assets $ 10,700