BUSINESS SEGMENT INFORMATION - Revenues by major service lines (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Segment information:
Revenues	$ 358,516	$ 467,926	$ 693,172	$ 904,260
Technical Services
Segment information:
Revenues	338,034	449,852	652,113	868,915
Technical Services | Pressure Pumping
Segment information:
Revenues	170,066	269,040	317,825	525,195
Technical Services | Downhole Tools
Segment information:
Revenues	112,763	107,521	222,434	200,562
Technical Services | Coiled Tubing
Segment information:
Revenues	21,284	27,404	41,462	52,600
Technical Services | Nitrogen
Segment information:
Revenues	12,219	11,784	23,527	23,215
Technical Services | Snubbing
Segment information:
Revenues	4,355	6,055	7,818	10,027
Technical Services | All other
Segment information:
Revenues	17,347	28,048	39,047	57,316
Support Services
Segment information:
Revenues	20,482	18,074	41,059	35,345
Support Services | Rental Tools
Segment information:
Revenues	13,962	12,550	27,898	22,570
Support Services | All other
Segment information:
Revenues	$ 6,520	$ 5,524	$ 13,161	$ 12,775