LEASES - Schedule of Lease Costs and Other Lease Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Lease cost:
Amortization of right-of-use assets	$ 1,025	$ 593	$ 2,616	$ 1,505
Interest expense	327	213	863	555
Fixed lease cost	4,291	4,308	12,347	12,851
Short-term lease cost	856	853	2,514	2,261
Variable lease cost	141	329	402	712
Total lease cost	6,640	6,296	18,742	17,884
Cash paid for amounts included in the measurement of lease liabilities:
Financing cash flows for finance leases	1,304	666	3,246	1,870
Operating cash flows for operating leases	3,874	2,963	9,588	9,837
Right-of-use assets obtained in exchange for new finance lease liabilities	5,078	0	16,871	6,857
Right-of-use assets obtained in exchange for new operating lease liabilities	$ 147	831	$ 3,289	1,419
Weighted-average remaining lease term - finance leases (years)	5 years 10 months 24 days		5 years 10 months 24 days
Weighted-average remaining lease term - operating leases (years)	11 years 8 months 12 days		11 years 8 months 12 days
Weighted-average discount rate - finance leases	4.30%		4.30%
Weighted-average discount rate - operating leases	5.10%		5.10%
Vehicles, equipment and property
Lease cost:
Fixed lease cost	$ 2,048	2,351	$ 6,636	7,271
Landfill
Lease cost:
Fixed lease cost	$ 2,243	$ 1,957	$ 5,711	$ 5,580