BUSINESS SEGMENT INFORMATION - Operating segment revenues by major service lines (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Segment Reporting Information [Line Items]
Revenues	$ 467,926	$ 398,810	$ 904,260	$ 696,929
Operating Segments
Segment Reporting Information [Line Items]
Revenues	467,926	398,810	904,260	696,929
Operating Segments | Technical Services
Segment Reporting Information [Line Items]
Revenues	449,852	385,462	868,915	671,660
Operating Segments | Pressure Pumping
Segment Reporting Information [Line Items]
Revenues	269,040	253,743	525,195	436,675
Operating Segments | Downhole Tools
Segment Reporting Information [Line Items]
Revenues	107,521	71,862	200,562	124,207
Operating Segments | Coiled Tubing
Segment Reporting Information [Line Items]
Revenues	27,404	25,956	52,600	47,335
Operating Segments | Nitrogen
Segment Reporting Information [Line Items]
Revenues	11,784	9,271	23,215	17,948
Operating Segments | Snubbing
Segment Reporting Information [Line Items]
Revenues	6,055	6,588	10,027	12,231
Operating Segments | All Other Technical Services
Segment Reporting Information [Line Items]
Revenues	28,048	18,042	57,316	33,264
Operating Segments | Support Services
Segment Reporting Information [Line Items]
Revenues	18,074	13,348	35,345	25,269
Operating Segments | Rental Tools
Segment Reporting Information [Line Items]
Revenues	12,550	6,459	22,570	11,847
Operating Segments | All Other Support Services
Segment Reporting Information [Line Items]
Revenues	$ 5,524	$ 6,889	$ 12,775	$ 13,422