BUSINESS SEGMENT INFORMATION - Operating segment revenues by major service lines (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting Information [Line Items]
Revenues	$ 439,994	$ 470,999	$ 1,344,254	$ 1,167,928
Operating Segments
Segment Reporting Information [Line Items]
Revenues	439,994	470,999	1,344,254	1,167,928
Operating Segments | Technical Services
Segment Reporting Information [Line Items]
Revenues	421,271	455,719	1,290,186	1,127,379
Operating Segments | Pressure Pumping
Segment Reporting Information [Line Items]
Revenues	237,487	303,631	762,527	740,120
Operating Segments | Downhole Tools
Segment Reporting Information [Line Items]
Revenues	112,798	81,383	313,360	205,591
Operating Segments | Coiled Tubing
Segment Reporting Information [Line Items]
Revenues	26,248	32,385	78,848	79,720
Operating Segments | Nitrogen
Segment Reporting Information [Line Items]
Revenues	12,645	12,412	35,860	30,360
Operating Segments | Snubbing
Segment Reporting Information [Line Items]
Revenues	4,257	5,385	14,284	17,616
Operating Segments | All Other Technical Services
Segment Reporting Information [Line Items]
Revenues	27,836	20,523	85,307	53,972
Operating Segments | Support Services
Segment Reporting Information [Line Items]
Revenues	18,723	15,280	54,068	40,549
Operating Segments | Rental Tools
Segment Reporting Information [Line Items]
Revenues	13,957	8,547	36,527	20,394
Operating Segments | All Other Support Services
Segment Reporting Information [Line Items]
Revenues	$ 4,766	$ 6,733	$ 17,541	$ 20,155