SEGMENT AND GEOGRAPHIC DISCLOSURES - Geographic Breakdown of Revenues (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2020	Mar. 31, 2019
Revenues from External Customers [Line Items]
Revenues	[1]	$ 236,839	$ 269,599
United States
Revenues from External Customers [Line Items]
Revenues	[1]	173,510	206,108
Canada
Revenues from External Customers [Line Items]
Revenues	[1]	21,209	19,321
Europe
Revenues from External Customers [Line Items]
Revenues	[1]	28,546	28,496
Other foreign countries
Revenues from External Customers [Line Items]
Revenues	[1]	$ 13,574	$ 15,674

[1] Revenues attributable to individual countries/geographic areas are based on the country of domicile of the legal entity that performs the work.