REVENUES (Tables)

9 Months Ended

Sep. 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 September 30, 2021
	Environmental Services		Safety-Kleen Sustainability Solutions		Corporate		Total
Primary Geographical Markets
United States	$	632,755	$	185,096	$	59	$	817,910
Canada	111,076		22,493		—		133,569
Total third-party revenues	$	743,831	$	207,589	$	59	$	951,479
Sources of Revenue
Technical Services	$	308,158	$	—	$	—	$	308,158
Field and Emergency Response Services	116,677		—		—		116,677
Industrial Services and Other	154,977		—		59		155,036
Safety-Kleen Environmental Services	164,019		39,551		—		203,570
Safety-Kleen Oil	—		168,038		—		168,038
Total third-party revenues	$	743,831	$	207,589	$	59	$	951,479

	For the Three Months Ended September 30, 2020
	Environmental Services		Safety-Kleen Sustainability Solutions		Corporate		Total
Primary Geographical Markets
United States	$	554,050	$	112,785	$	(186)	$	666,649
Canada	97,639		14,798		258		112,695
Total third-party revenues	$	651,689	$	127,583	$	72	$	779,344
Sources of Revenue
Technical Services	$	257,612	$	—	$	—	$	257,612
Field and Emergency Response Services	115,989		—		—		115,989
Industrial Services and Other	124,582		—		72		124,654
Safety-Kleen Environmental Services	153,506		49,949		—		203,455
Safety-Kleen Oil	—		77,634		—		77,634
Total third-party revenues	$	651,689	$	127,583	$	72	$	779,344

	For the Nine Months Ended September 30, 2021
	Environmental Services		Safety-Kleen Sustainability Solutions		Corporate		Total
Primary Geographical Markets
United States	$	1,824,848	$	504,302	$	217	$	2,329,367
Canada	295,008		61,710		—		356,718
Total third-party revenues	$	2,119,856	$	566,012	$	217	$	2,686,085
Sources of Revenue
Technical Services	$	887,063	$	—	$	—	$	887,063
Field and Emergency Response Services	328,831		—		—		328,831
Industrial Services and Other	425,154		—		217		425,371
Safety-Kleen Environmental Services	478,808		118,982		—		597,790
Safety-Kleen Oil	—		447,030		—		447,030
Total third-party revenues	$	2,119,856	$	566,012	$	217	$	2,686,085

	For the Nine Months Ended September 30, 2020
	Environmental Services		Safety-Kleen Sustainability Solutions		Corporate		Total
Primary Geographical Markets
United States	$	1,704,945	$	340,226	$	(648)	$	2,044,523
Canada	264,500		38,018		866		303,384
Total third-party revenues	$	1,969,445	$	378,244	$	218	$	2,347,907
Sources of Revenue
Technical Services	$	774,814	$	—	$	—	$	774,814
Field and Emergency Response Services	349,254		—		—		349,254
Industrial Services and Other	366,573		—		218		366,791
Safety-Kleen Environmental Services	478,804		134,004		—		612,808
Safety-Kleen Oil	—		244,240		—		244,240
Total third-party revenues	$	1,969,445	$	378,244	$	218	$	2,347,907

Schedule of Contract Balances

(in thousands)	September 30, 2021		December 31, 2020
Receivables	$	703,199	$	611,534
Contract assets (unbilled receivables)	69,912		55,681
Contract liabilities (deferred revenue)	86,589		74,066