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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 |  |

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