SEGMENT AND GEOGRAPHIC DISCLOSURES - Geographic Breakdown of Revenues (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	[1]	Jun. 30, 2019	[1]
Revenues from External Customers [Line Items]
Revenues	$ 189,304	$ 315,829	$ 426,143		$ 585,428
United States
Revenues from External Customers [Line Items]
Revenues	141,950	230,563	315,460		436,671
Canada
Revenues from External Customers [Line Items]
Revenues	14,435	35,330	35,643		54,651
Europe
Revenues from External Customers [Line Items]
Revenues	23,097	34,882	51,643		63,378
Other foreign countries
Revenues from External Customers [Line Items]
Revenues	$ 9,822	$ 15,054	$ 23,397		$ 30,728

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