REVENUE RECOGNITION - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Disaggregation of Revenue [Line Items]
Total revenues	$ 198,547	$ 172,832	$ 549,670	$ 485,936
Transferred at a point-in-time
Disaggregation of Revenue [Line Items]
Total revenues	5,970	8,935	19,441	24,877
Transferred over time
Disaggregation of Revenue [Line Items]
Total revenues	192,577	163,897	530,229	461,059
Collection
Disaggregation of Revenue [Line Items]
Total revenues	101,191	80,844	278,433	223,348
Landfill
Disaggregation of Revenue [Line Items]
Total revenues	25,432	27,100	68,899	71,683
Transfer
Disaggregation of Revenue [Line Items]
Total revenues	21,941	18,291	56,723	50,212
Customer solutions
Disaggregation of Revenue [Line Items]
Total revenues	20,689	17,195	58,058	48,315
Recycling
Disaggregation of Revenue [Line Items]
Total revenues	11,191	11,757	33,254	33,905
Organics
Disaggregation of Revenue [Line Items]
Total revenues	14,166	13,413	42,668	40,259
Transportation
Disaggregation of Revenue [Line Items]
Total revenues	3,129	3,312	8,980	14,200
Landfill gas-to-energy
Disaggregation of Revenue [Line Items]
Total revenues	808	920	2,655	4,014
Eastern
Disaggregation of Revenue [Line Items]
Total revenues	59,675	56,006	163,748	154,099
Eastern | Transferred at a point-in-time
Disaggregation of Revenue [Line Items]
Total revenues	36	128	123	500
Eastern | Transferred over time
Disaggregation of Revenue [Line Items]
Total revenues	59,639	55,878	163,625	153,599
Eastern | Collection
Disaggregation of Revenue [Line Items]
Total revenues	41,868	36,392	115,363	101,544
Eastern | Landfill
Disaggregation of Revenue [Line Items]
Total revenues	5,414	8,336	14,558	22,179
Eastern | Transfer
Disaggregation of Revenue [Line Items]
Total revenues	12,247	11,001	33,157	29,305
Eastern | Customer solutions
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Eastern | Recycling
Disaggregation of Revenue [Line Items]
Total revenues	4	5	5	0
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	142	272	665	1,071
Western
Disaggregation of Revenue [Line Items]
Total revenues	92,871	74,425	251,860	210,208
Western | Transferred at a point-in-time
Disaggregation of Revenue [Line Items]
Total revenues	186	233	673	847
Western | Transferred over time
Disaggregation of Revenue [Line Items]
Total revenues	92,685	74,192	251,187	209,361
Western | Collection
Disaggregation of Revenue [Line Items]
Total revenues	59,323	44,452	163,070	121,804
Western | Landfill
Disaggregation of Revenue [Line Items]
Total revenues	20,018	18,764	54,341	49,504
Western | Transfer
Disaggregation of Revenue [Line Items]
Total revenues	9,694	7,290	23,566	20,907
Western | Customer solutions
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Western | Recycling
Disaggregation of Revenue [Line Items]
Total revenues	461	875	1,243	3,271
Western | Organics
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Western | Transportation
Disaggregation of Revenue [Line Items]
Total revenues	2,709	2,396	7,650	11,779
Western | Landfill gas-to-energy
Disaggregation of Revenue [Line Items]
Total revenues	666	648	1,990	2,943
Recycling
Disaggregation of Revenue [Line Items]
Total revenues	10,726	10,877	32,006	30,634
Recycling | Transferred at a point-in-time
Disaggregation of Revenue [Line Items]
Total revenues	4,592	7,436	15,768	20,311
Recycling | Transferred over time
Disaggregation of Revenue [Line Items]
Total revenues	6,134	3,441	16,238	10,323
Recycling | Collection
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Recycling | Landfill
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Recycling | Transfer
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Recycling | Customer solutions
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Recycling | Recycling
Disaggregation of Revenue [Line Items]
Total revenues	10,726	10,877	32,006	30,634
Recycling | Organics
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Recycling | Transportation
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Recycling | Landfill gas-to-energy
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Other
Disaggregation of Revenue [Line Items]
Total revenues	35,275	31,524	102,056	90,995
Other | Transferred at a point-in-time
Disaggregation of Revenue [Line Items]
Total revenues	1,156	1,138	2,877	3,219
Other | Transferred over time
Disaggregation of Revenue [Line Items]
Total revenues	34,119	30,386	99,179	87,776
Other | Collection
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Other | Landfill
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Other | Transfer
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Other | Customer solutions
Disaggregation of Revenue [Line Items]
Total revenues	20,689	17,195	58,058	48,315
Other | Recycling
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Other | Organics
Disaggregation of Revenue [Line Items]
Total revenues	14,166	13,413	42,668	40,259
Other | Transportation
Disaggregation of Revenue [Line Items]
Total revenues	420	916	1,330	2,421
Other | Landfill gas-to-energy
Disaggregation of Revenue [Line Items]
Total revenues	$ 0	$ 0	$ 0	$ 0