SIGNIFICANT ACCOUNTING POLICIES (Tables)

12 Months Ended

Dec. 31, 2019

Schedule of Cash Equivalents and Marketable Securities

As of December 31, 2019 and 2018, the Company had total marketable securities and cash equivalents as follows (in thousands):



	December 31, 2019		December 31, 2018
Commercial paper	$	2,395	$	8,126
Total cash equivalents	2,395		8,126

U.S. Treasury securities	12,406		10,133
Corporate notes and bonds	26,678		38,036
Commercial paper	3,337		4,687
Total short-term marketable securities	42,421		52,856
Total financial assets	$	44,816	$	60,982

Schedule of Asset Classification and Estimated Useful Life

The Company depreciates and amortizes the capitalized cost of these assets, using the straight-line method as follows:



Asset Classification		Estimated Useful Life
Buildings and building improvements
Buildings		20-42 years
Leasehold and building improvements		2-45 years
Camp and lodging equipment		8-15 years
Vehicles		2-15 years
Equipment
Capitalized software and computer equipment		3-5 years
Containers and railcars		8-16 years
All other equipment		4-30 years
Furniture and fixtures		5-8 years

Property, plant and equipment consisted of the following (in thousands):



	December 31, 2019		December 31, 2018
Land	$	131,023	$	123,734
Asset retirement costs (non-landfill)	15,924		15,148
Landfill assets	182,276		154,918
Buildings and improvements ⁽¹⁾	499,159		440,188
Camp and lodging equipment	158,277		152,998
Vehicles ⁽¹⁾	785,056		721,735
Equipment	1,779,366		1,697,490
Furniture and fixtures	6,054		5,453
Construction in progress	36,679		20,931
	3,593,814		3,332,595
Less - accumulated depreciation and amortization	2,005,663		1,770,617
Total property, plant and equipment, net	$	1,588,151	$	1,561,978

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(1)

December 31, 2019 balances inclusive of ROU assets classified as finance leases.

Schedule of Active Landfill Sites

As of December 31, 2019, the Company had 11 active landfill sites (including the Company's two non-commercial landfills), which have estimated remaining lives (based on anticipated waste volumes and remaining highly probable airspace) as follows:



		Remaining Lives (Years)	Remaining Highly Probable Airspace (cubic yards) (in thousands)
Facility Name	Location	Remaining Lives (Years)	Permitted	Unpermitted	Total
Altair	Texas	2	179	—	179
Buttonwillow	California	23	5,982	—	5,982
Deer Park	Texas	3	103	—	103
Deer Trail	Colorado	28	1,697	—	1,697
Grassy Mountain	Utah	43	4,909	—	4,909
Kimball	Nebraska	7	165	—	165
Lambton	Ontario, Canada	60	4,710	—	4,710
Lone Mountain	Oklahoma	23	3,905	—	3,905
Ryley	Alberta	5	653	—	653
Sawyer	North Dakota	69	3,459	—	3,459
Westmorland	California	64	2,732	—	2,732
			28,494	—	28,494

Remaining Highly Probable Airspace

The following table presents the remaining highly probable airspace from January 1, 2017 through December 31, 2019 (in thousands of cubic yards):



	2019		2018		2017
Remaining capacity at January 1,	29,760		31,113		32,228
Changes in highly probable airspace, net	—		(223	)	—
Consumed	(1,266	)	(1,130	)	(1,115	)
Remaining capacity at December 31,	28,494		29,760		31,113