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Segment Reporting (Changes in Goodwill by Reportable Segment) (Detail) - USD ($)
$ in Thousands
 9 Months Ended 12 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Dec. 31, 2016
Goodwill [Line Items]      
Goodwill, Beginning Balance $ 4,390,261 $ 1,422,825 $ 1,422,825
Goodwill acquired 309,031 2,931,223  
Goodwill divested (36,486)    
Impairment loss (77,343)    
Goodwill adjustment for assets sold 2,526    
Goodwill adjustment for assets held for sale (11,080)    
Impact of changes in foreign currency 111,439 (2,878)  
Goodwill, Ending Balance 4,688,348 4,351,170 4,390,261
Southern [Member]      
Goodwill [Line Items]      
Goodwill, Beginning Balance 1,470,023 95,710 95,710
Goodwill acquired 7,484 1,338,806  
Goodwill divested (31,543)    
Goodwill adjustment for assets sold 2,205    
Goodwill adjustment for assets held for sale (11,080)    
Goodwill, Ending Balance 1,437,089 1,434,516 1,470,023
Western [Member]      
Goodwill [Line Items]      
Goodwill, Beginning Balance 376,537 373,820 373,820
Goodwill acquired 20,906 2,696  
Goodwill, Ending Balance 397,443 376,516 376,537
Eastern [Member]      
Goodwill [Line Items]      
Goodwill, Beginning Balance 533,160 459,532 459,532
Goodwill acquired 272,501 75,769  
Goodwill divested (4,276)    
Goodwill adjustment for assets sold 321    
Goodwill, Ending Balance 801,706 535,301 533,160
Canada [Member]      
Goodwill [Line Items]      
Goodwill, Beginning Balance 1,465,274    
Goodwill acquired 7,127 1,465,720  
Impact of changes in foreign currency 111,439 (2,878)  
Goodwill, Ending Balance 1,583,840 1,462,842 1,465,274
Central [Member]      
Goodwill [Line Items]      
Goodwill, Beginning Balance 467,924 416,420 416,420
Goodwill acquired 1,013 48,232  
Goodwill divested (667)    
Goodwill, Ending Balance 468,270 464,652 467,924
Exploration and Production [Member]      
Goodwill [Line Items]      
Goodwill, Beginning Balance 77,343 77,343 77,343
Impairment loss $ (77,343)   0
Goodwill, Ending Balance   $ 77,343 $ 77,343