SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES AND PRACTICES - Schedule of Rollforward Goodwill (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Goodwill [Line Items]
Accumulated impairment loss	$ 75,200	$ 75,200
Goodwill [Roll Forward]
Balance at beginning of period	284,804
Foreign currency adjustments	(1,714)
Balance at end of period	283,090
IHT
Goodwill [Line Items]
Accumulated impairment loss	21,100	21,100
Goodwill [Roll Forward]
Balance at beginning of period	194,211
Foreign currency adjustments	(905)
Balance at end of period	193,306
MS
Goodwill [Line Items]
Accumulated impairment loss	54,100	$ 54,100
Goodwill [Roll Forward]
Balance at beginning of period	56,600
Foreign currency adjustments	(390)
Balance at end of period	56,210
Quest Integrity
Goodwill [Roll Forward]
Balance at beginning of period	33,993
Foreign currency adjustments	(419)
Balance at end of period	$ 33,574