REVENUES (Tables)

3 Months Ended

Mar. 31, 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 March 31, 2021
	Environmental Services		Safety-Kleen Sustainability Solutions		Corporate		Total
Primary Geographical Markets
United States	$	575,508	$	138,990	$	79	$	714,577
Canada	77,370		16,201		—		93,571
Total third-party revenues	$	652,878	$	155,191	$	79	$	808,148
Sources of Revenue
Technical Services	$	272,040	$	—	$	—	$	272,040
Field and Emergency Response Services	105,168		—		—		105,168
Industrial Services and Other	119,810		—		79		119,889
Safety-Kleen Environmental Services	155,860		38,978		—		194,838
Safety-Kleen Oil	—		116,213		—		116,213
Total third-party revenues	$	652,878	$	155,191	$	79	$	808,148

	For the Three Months Ended March 31, 2020
	Environmental Services		Safety-Kleen Sustainability Solutions		Corporate		Total
Primary Geographical Markets
United States	$	607,110	$	139,437	$	(302)	$	746,245
Canada	97,926		14,000		392		112,318
Total third-party revenues	$	705,036	$	153,437	$	90	$	858,563
Sources of Revenue
Technical Services	$	275,273	$	—	$	—	$	275,273
Field and Emergency Response Services	105,912		—		—		105,912
Industrial Services and Other	146,919		—		90		147,009
Safety-Kleen Environmental Services	176,932		37,549		—		214,481
Safety-Kleen Oil	—		115,888		—		115,888
Total third-party revenues	$	705,036	$	153,437	$	90	$	858,563

Schedule of Contract Balances

(in thousands)	March 31, 2021		December 31, 2020
Receivables	$	620,184	$	611,534
Contract assets (unbilled receivables)	55,239		55,681
Contract liabilities (deferred revenue)	83,165		74,066