BUSINESS SEGMENT INFORMATION - Revenues by major service lines (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Segment information:
Revenues	$ 293,240	$ 439,994	$ 986,412	$ 1,344,254
Technical Services
Segment information:
Revenues	274,483	421,271	926,596	1,290,186
Technical Services | Pressure Pumping
Segment information:
Revenues	111,163	237,487	428,988	762,527
Technical Services | Downhole Tools
Segment information:
Revenues	111,619	112,798	334,053	313,360
Technical Services | Coiled Tubing
Segment information:
Revenues	19,622	26,248	61,084	78,848
Technical Services | Nitrogen
Segment information:
Revenues	10,140	12,645	33,667	35,860
Technical Services | Snubbing
Segment information:
Revenues	4,407	4,257	12,225	14,284
Technical Services | All other
Segment information:
Revenues	17,532	27,836	56,579	85,307
Support Services
Segment information:
Revenues	18,757	18,723	59,816	54,068
Support Services | Rental Tools
Segment information:
Revenues	12,479	13,957	40,377	36,527
Support Services | All other
Segment information:
Revenues	$ 6,278	$ 4,766	$ 19,439	$ 17,541