BUSINESS SEGMENT INFORMATION - Operating segment revenues by major service lines (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Segment Reporting Information [Line Items]
Revenues	$ 334,656	$ 436,334
Operating Segments
Segment Reporting Information [Line Items]
Revenues	334,656	436,334
Operating Segments | Technical Services
Segment Reporting Information [Line Items]
Revenues	314,079	419,063
Operating Segments | Pressure Pumping
Segment Reporting Information [Line Items]
Revenues	147,759	256,155
Operating Segments | Downhole Tools
Segment Reporting Information [Line Items]
Revenues	109,671	93,041
Operating Segments | Coiled Tubing
Segment Reporting Information [Line Items]
Revenues	20,178	25,196
Operating Segments | Nitrogen
Segment Reporting Information [Line Items]
Revenues	11,308	11,431
Operating Segments | Snubbing
Segment Reporting Information [Line Items]
Revenues	3,463	3,973
Operating Segments | All Other Technical Services
Segment Reporting Information [Line Items]
Revenues	21,700	29,267
Operating Segments | Support Services
Segment Reporting Information [Line Items]
Revenues	20,577	17,271
Operating Segments | Rental Tools
Segment Reporting Information [Line Items]
Revenues	13,936	10,020
Operating Segments | All Other Support Services
Segment Reporting Information [Line Items]
Revenues	$ 6,641	$ 7,251