REVENUES (Tables)

6 Months Ended

Jun. 30, 2021

Revenue from Contract with Customer [Abstract]

Schedule of Disaggregation of Revenue

We disaggregate the Company's third party revenues by geographic location and source of revenue as we believe these categories depict how revenue and cash flows are affected by economic factors (in thousands):

	For the Three Months Ended June 30, 2021
	Environmental Services		Safety-Kleen Sustainability Solutions		Corporate		Total
Primary Geographical Markets
United States	$	616,585	$	180,216	$	79	$	796,880
Canada	106,562		23,016		—		129,578
Total third-party revenues	$	723,147	$	203,232	$	79	$	926,458
Sources of Revenue
Technical Services	$	306,865	$	—	$	—	$	306,865
Field and Emergency Response Services	106,986		—		—		106,986
Industrial Services and Other	150,367		—		79		150,446
Safety-Kleen Environmental Services	158,929		40,453		—		199,382
Safety-Kleen Oil	—		162,779		—		162,779
Total third-party revenues	$	723,147	$	203,232	$	79	$	926,458

	For the Three Months Ended June 30, 2020
	Environmental Services		Safety-Kleen Sustainability Solutions		Corporate		Total
Primary Geographical Markets
United States	$	543,785	$	88,004	$	(160)	$	631,629
Canada	68,935		9,220		216		78,371
Total third-party revenues	$	612,720	$	97,224	$	56	$	710,000
Sources of Revenue
Technical Services	$	241,929	$	—	$	—	$	241,929
Field and Emergency Response Services	127,353		—		—		127,353
Industrial Services and Other	95,072		—		56		95,128
Safety-Kleen Environmental Services	148,366		46,506		—		194,872
Safety-Kleen Oil	—		50,718		—		50,718
Total third-party revenues	$	612,720	$	97,224	$	56	$	710,000

	For the Six Months Ended June 30, 2021
	Environmental Services		Safety-Kleen Sustainability Solutions		Corporate		Total
Primary Geographical Markets
United States	$	1,192,093	$	319,206	$	158	$	1,511,457
Canada	183,932		39,217		—		223,149
Total third-party revenues	$	1,376,025	$	358,423	$	158	$	1,734,606
Sources of Revenue
Technical Services	$	578,905	$	—	$	—	$	578,905
Field and Emergency Response Services	212,154		—		—		212,154
Industrial Services and Other	270,177		—		158		270,335
Safety-Kleen Environmental Services	314,789		79,431		—		394,220
Safety-Kleen Oil	—		278,992		—		278,992
Total third-party revenues	$	1,376,025	$	358,423	$	158	$	1,734,606

	For the Six Months Ended June 30, 2020
	Environmental Services		Safety-Kleen Sustainability Solutions		Corporate		Total
Primary Geographical Markets
United States	$	1,150,895	$	227,441	$	(462)	$	1,377,874
Canada	166,861		23,220		608		190,689
Total third-party revenues	$	1,317,756	$	250,661	$	146	$	1,568,563
Sources of Revenue
Technical Services	$	517,202	$	—	$	—	$	517,202
Field and Emergency Response Services	233,265		—		—		233,265
Industrial Services and Other	241,991		—		146		242,137
Safety-Kleen Environmental Services	325,298		84,055		—		409,353
Safety-Kleen Oil	—		166,606		—		166,606
Total third-party revenues	$	1,317,756	$	250,661	$	146	$	1,568,563

Schedule of Contract Balances

(in thousands)	June 30, 2021		December 31, 2020
Receivables	$	659,364	$	611,534
Contract assets (unbilled receivables)	59,446		55,681
Contract liabilities (deferred revenue)	83,733		74,066