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Landfill Accounting (Narrative) (Details)
$ in Thousands
 9 Months Ended 12 Months Ended
Sep. 30, 2018
USD ($)
site
$ / T
Sep. 30, 2017
USD ($)
$ / T
Dec. 31, 2017
USD ($)
Landfill Accounting [Line Items]      
Number of landfills owned and operated by company | site 81    
Number of landfills operated, not owned, under life-of-site operating agreements | site 8    
Number of landfills operated under limited-term operating agreements | site 4    
Property and equipment, net $ 5,069,767   $ 4,820,934
Average remaining landfill life based on permitted capacity and projected annual disposal volumes 26 years    
Number of owned landfills the company is seeking to expand | site 11    
Number of landfills operated under life-of-site operating agreements that the company is seeking to expand | site 3    
Average remaining landfill life based on permitted capacity, projected annual disposal volumes and probable expansion capacity 30 years    
Life of Company's owned landfills and landfills operated under life-of-site operating agreements min range 1 year    
Life of Company's owned landfills and landfills operated under life of site operating agreements max range 158 years    
Landfill depletion expense $ 153,010 $ 147,071  
Average rate per ton consumed related to landfill depletion at owned landfills and landfills operated under life-of-site agreements | $ / T 4.58 4.55  
Inflation rate for purposes of computing layers for final capping, closure and post-closure obligations 2.50%   2.50%
Accretion expense associated with landfill obligations $ 9,583 $ 8,757  
Average rate per ton consumed related to final capping, closure and post-closure landfill accretion expense | $ / T 0.29 0.27  
Restricted asset balance for purposes of securing our performance of future final capping, closure and post-closure obligations $ 44,760   $ 43,684
Restricted investments 12,639   $ 12,406
Liabilities incurred 11,750    
Landfill [Member]      
Landfill Accounting [Line Items]      
Property and equipment, net $ 2,868,628    
Fair value discount rate 4.75%   4.75%