REVENUE Disaggregation of Revenue - Industry (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Disaggregation of Revenue [Line Items]
Revenues	$ 2,221,622	$ 2,161,306
SCS
Disaggregation of Revenue [Line Items]
Revenues	706,700	628,447
Automotive | SCS
Disaggregation of Revenue [Line Items]
Revenues	271,555	249,925
Technology and healthcare | SCS
Disaggregation of Revenue [Line Items]
Revenues	97,085	91,133
Consumer packaged goods and retail | SCS
Disaggregation of Revenue [Line Items]
Revenues	273,224	229,932
Industrial and other | SCS
Disaggregation of Revenue [Line Items]
Revenues	$ 64,836	$ 57,457