REVENUE RECOGNITION - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Disaggregation of Revenue [Line Items]
Total revenues	$ 202,667	$ 198,547	$ 574,344	$ 549,670
Transferred at a point-in-time
Disaggregation of Revenue [Line Items]
Total revenues	8,135	5,970	21,554	19,441
Transferred over time
Disaggregation of Revenue [Line Items]
Total revenues	194,532	192,577	552,790	530,229
Collection
Disaggregation of Revenue [Line Items]
Total revenues	104,171	101,191	295,282	278,433
Landfill
Disaggregation of Revenue [Line Items]
Total revenues	23,574	25,432	63,216	68,899
Transfer
Disaggregation of Revenue [Line Items]
Total revenues	21,617	21,941	58,173	56,723
Customer solutions
Disaggregation of Revenue [Line Items]
Total revenues	22,320	20,689	64,223	58,058
Recycling
Disaggregation of Revenue [Line Items]
Total revenues	13,111	11,191	37,157	33,254
Organics
Disaggregation of Revenue [Line Items]
Total revenues	14,539	14,166	44,890	42,668
Transportation
Disaggregation of Revenue [Line Items]
Total revenues	2,348	3,129	8,472	8,980
Landfill gas-to-energy
Disaggregation of Revenue [Line Items]
Total revenues	987	808	2,931	2,655
Eastern
Disaggregation of Revenue [Line Items]
Total revenues	58,323	59,675	161,803	163,748
Eastern | Transferred at a point-in-time
Disaggregation of Revenue [Line Items]
Total revenues	52	36	177	123
Eastern | Transferred over time
Disaggregation of Revenue [Line Items]
Total revenues	58,271	59,639	161,626	163,625
Eastern | Collection
Disaggregation of Revenue [Line Items]
Total revenues	40,560	41,868	114,504	115,363
Eastern | Landfill
Disaggregation of Revenue [Line Items]
Total revenues	5,694	5,414	13,807	14,558
Eastern | Transfer
Disaggregation of Revenue [Line Items]
Total revenues	11,861	12,247	32,695	33,157
Eastern | Customer solutions
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Eastern | Recycling
Disaggregation of Revenue [Line Items]
Total revenues	(2)	4	4	5
Eastern | Organics
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Eastern | Transportation
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Eastern | Landfill gas-to-energy
Disaggregation of Revenue [Line Items]
Total revenues	210	142	793	665
Western
Disaggregation of Revenue [Line Items]
Total revenues	94,728	93,291	267,218	253,190
Western | Transferred at a point-in-time
Disaggregation of Revenue [Line Items]
Total revenues	347	186	949	673
Western | Transferred over time
Disaggregation of Revenue [Line Items]
Total revenues	94,381	93,105	266,269	252,517
Western | Collection
Disaggregation of Revenue [Line Items]
Total revenues	63,611	59,323	180,778	163,070
Western | Landfill
Disaggregation of Revenue [Line Items]
Total revenues	17,880	20,018	49,409	54,341
Western | Transfer
Disaggregation of Revenue [Line Items]
Total revenues	9,756	9,694	25,478	23,566
Western | Customer solutions
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Western | Recycling
Disaggregation of Revenue [Line Items]
Total revenues	356	461	943	1,243
Western | Organics
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Western | Transportation
Disaggregation of Revenue [Line Items]
Total revenues	2,348	3,129	8,472	8,980
Western | Landfill gas-to-energy
Disaggregation of Revenue [Line Items]
Total revenues	777	666	2,138	1,990
Resource Solutions
Disaggregation of Revenue [Line Items]
Total revenues	49,616	45,581	145,323	132,732
Resource Solutions | Transferred at a point-in-time
Disaggregation of Revenue [Line Items]
Total revenues	7,736	5,748	20,428	18,645
Resource Solutions | Transferred over time
Disaggregation of Revenue [Line Items]
Total revenues	41,880	39,833	124,895	114,087
Resource Solutions | Collection
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Resource Solutions | Landfill
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Resource Solutions | Transfer
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Resource Solutions | Customer solutions
Disaggregation of Revenue [Line Items]
Total revenues	22,320	20,689	64,223	58,058
Resource Solutions | Recycling
Disaggregation of Revenue [Line Items]
Total revenues	12,757	10,726	36,210	32,006
Resource Solutions | Organics
Disaggregation of Revenue [Line Items]
Total revenues	14,539	14,166	44,890	42,668
Resource Solutions | Transportation
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Resource Solutions | Landfill gas-to-energy
Disaggregation of Revenue [Line Items]
Total revenues	$ 0	$ 0	$ 0	$ 0