REVENUE Disaggregation of Revenue - Industry (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Disaggregation of Revenue [Line Items]
Total revenue	$ 2,244,993	$ 2,089,904	$ 4,425,320	$ 3,994,109
SCS
Disaggregation of Revenue [Line Items]
Total revenue	649,311	604,524	1,284,982	1,099,231
Automotive | SCS
Disaggregation of Revenue [Line Items]
Total revenue	261,288	231,886	514,967	439,678
Technology and healthcare | SCS
Disaggregation of Revenue [Line Items]
Total revenue	110,054	114,388	223,723	217,485
CPG and retail | SCS
Disaggregation of Revenue [Line Items]
Total revenue	225,582	197,694	442,679	333,052
Industrial and other | SCS
Disaggregation of Revenue [Line Items]
Total revenue	$ 52,387	$ 60,556	$ 103,613	$ 109,016