SIGNIFICANT ACCOUNTING POLICIES (Landfill Accounting) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($) service_location expansion landfill_site cubic_yard	Dec. 31, 2017 USD ($) cubic_yard	Dec. 31, 2016 USD ($) cubic_yard
Property, Plant and Equipment [Line Items]
Application approvals, acceptance period (in years)	5 years
Number of unpermitted expansions | expansion	1
Number of service locations | service_location	1
Percentage of airspace remaining (as a percent)	16.20%
Landfill sites | landfill_site	11
Remaining highly probable airspace	29,760,000
Permitted, but not highly probable airspace (cubic yards)	0	0
Remaining Airspace Capacity [Roll Forward]
Remaining capacity, beginning of period (cubic yards)	31,113,000	32,228,000	29,786,000
Changes in highly probable airspace, net (cubic yards)	(223,000)	0	3,464,000
Consumed (cubic yards)	(1,130,000)	(1,115,000)	(1,022,000)
Remaining capacity, end of period (cubic yards)	29,760,000	31,113,000	32,228,000
Landfill final closure and post-closure liabilities | $	$ 37.8	$ 32.4
Regulatory post-closure period for landfill (in years)	30 years
Asset retirement obligations, inflation rate (as a percent)	1.02%	1.02%
Asset retirement obligations, risk free rate (as a percent)	5.66%	6.32%
Non-landfill closure and post-closure liabilities | $	$ 32.1	$ 28.6
Minimum
Remaining Airspace Capacity [Roll Forward]
Non-landfill closure and post-closure liabilities, period (in years)	10 years
Maximum
Remaining Airspace Capacity [Roll Forward]
Non-landfill closure and post-closure liabilities, period (in years)	30 years
Landfill assets
Property, Plant and Equipment [Line Items]
Amortization | $	$ 10.3	$ 9.5	$ 9.7
Non-commercial landfills
Property, Plant and Equipment [Line Items]
Landfill sites | landfill_site	2
Permitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	24,930,000
Unpermitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	4,830,000
Altair | Texas
Property, Plant and Equipment [Line Items]
Remaining Lives (Years)	3 years
Remaining highly probable airspace	311,000
Altair | Texas | Permitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	311,000
Altair | Texas | Unpermitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	0
Buttonwillow | California
Property, Plant and Equipment [Line Items]
Remaining Lives (Years)	21 years
Remaining highly probable airspace	6,234,000
Buttonwillow | California | Permitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	6,234,000
Buttonwillow | California | Unpermitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	0
Deer Park | Texas
Property, Plant and Equipment [Line Items]
Remaining Lives (Years)	4 years
Remaining highly probable airspace	141,000
Deer Park | Texas | Permitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	141,000
Deer Park | Texas | Unpermitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	0
Deer Trail | Colorado
Property, Plant and Equipment [Line Items]
Remaining Lives (Years)	28 years
Remaining highly probable airspace	1,755,000
Deer Trail | Colorado | Permitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	1,755,000
Deer Trail | Colorado | Unpermitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	0
Grassy Mountain | Utah
Property, Plant and Equipment [Line Items]
Remaining Lives (Years)	51 years
Remaining highly probable airspace	5,024,000
Grassy Mountain | Utah | Permitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	194,000
Grassy Mountain | Utah | Unpermitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	4,830,000
Kimball | Nebraska
Property, Plant and Equipment [Line Items]
Remaining Lives (Years)	9 years
Remaining highly probable airspace	190,000
Kimball | Nebraska | Permitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	190,000
Kimball | Nebraska | Unpermitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	0
Lambton | Ontario
Property, Plant and Equipment [Line Items]
Remaining Lives (Years)	64 years
Remaining highly probable airspace	4,821,000
Lambton | Ontario | Permitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	4,821,000
Lambton | Ontario | Unpermitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	0
Lone Mountain | Oklahoma
Property, Plant and Equipment [Line Items]
Remaining Lives (Years)	18 years
Remaining highly probable airspace	4,124,000
Lone Mountain | Oklahoma | Permitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	4,124,000
Lone Mountain | Oklahoma | Unpermitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	0
Ryley | Alberta
Property, Plant and Equipment [Line Items]
Remaining Lives (Years)	7 years
Remaining highly probable airspace	906,000
Ryley | Alberta | Permitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	906,000
Ryley | Alberta | Unpermitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	0
Sawyer | North Dakota
Property, Plant and Equipment [Line Items]
Remaining Lives (Years)	87 years
Remaining highly probable airspace	3,522,000
Sawyer | North Dakota | Permitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	3,522,000
Sawyer | North Dakota | Unpermitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	0
Westmorland | California
Property, Plant and Equipment [Line Items]
Remaining Lives (Years)	64 years
Remaining highly probable airspace	2,732,000
Westmorland | California | Permitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	2,732,000
Westmorland | California | Unpermitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	0