SIGNIFICANT ACCOUNTING POLICIES (Landfill Accounting) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($) expansion landfill_site cubic_yard	Dec. 31, 2018 USD ($) cubic_yard	Dec. 31, 2017 USD ($) cubic_yard
Property, Plant and Equipment [Line Items]
Number of unpermitted expansions | expansion	0
Landfill sites | landfill_site	11
Remaining highly probable airspace	28,494,000
Permitted, but not highly probable airspace (cubic yards)	0	0
Remaining Airspace Capacity [Roll Forward]
Remaining capacity, beginning of period (cubic yards)	29,760,000	31,113,000	32,228,000
Changes in highly probable airspace, net (cubic yards)	0	(223,000)	0
Consumed (cubic yards)	(1,266,000)	(1,130,000)	(1,115,000)
Remaining capacity, end of period (cubic yards)	28,494,000	29,760,000	31,113,000
Landfill final closure and post-closure liabilities | $	$ 39.4	$ 37.8
Regulatory post-closure period for landfill (in years)	30 years
Asset retirement obligations, inflation rate (as a percent)	1.02%
Asset retirement obligations, risk free rate (as a percent)	6.02%	5.66%
Non-landfill closure and post-closure liabilities | $	$ 36.3	$ 32.1
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 | $	$ 12.3	$ 10.3	$ 9.5
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	28,494,000
Unpermitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	0
Altair | Texas
Property, Plant and Equipment [Line Items]
Remaining Lives (Years)	2 years
Remaining highly probable airspace	179,000
Altair | Texas | Permitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	179,000
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)	23 years
Remaining highly probable airspace	5,982,000
Buttonwillow | California | Permitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	5,982,000
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)	3 years
Remaining highly probable airspace	103,000
Deer Park | Texas | Permitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	103,000
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	1,697,000
Deer Trail | Colorado | Permitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	1,697,000
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)	43 years
Remaining highly probable airspace	4,909,000
Grassy Mountain | Utah | Permitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	4,909,000
Grassy Mountain | Utah | Unpermitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	0
Kimball | Nebraska
Property, Plant and Equipment [Line Items]
Remaining Lives (Years)	7 years
Remaining highly probable airspace	165,000
Kimball | Nebraska | Permitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	165,000
Kimball | Nebraska | Unpermitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	0
Lambton | Ontario, Canada
Property, Plant and Equipment [Line Items]
Remaining Lives (Years)	60 years
Remaining highly probable airspace	4,710,000
Lambton | Ontario, Canada | Permitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	4,710,000
Lambton | Ontario, Canada | Unpermitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	0
Lone Mountain | Oklahoma
Property, Plant and Equipment [Line Items]
Remaining Lives (Years)	23 years
Remaining highly probable airspace	3,905,000
Lone Mountain | Oklahoma | Permitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	3,905,000
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)	5 years
Remaining highly probable airspace	653,000
Ryley | Alberta | Permitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	653,000
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)	69 years
Remaining highly probable airspace	3,459,000
Sawyer | North Dakota | Permitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	3,459,000
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