BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Impact of Adoption on Unaudited Condensed Consolidated Statements of Operations (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Statement of operations:
Revenue from services	$ 15,003		$ 69,009
Cost of services	16,085		61,800
Income taxes	1,364	$ 1,950	107	$ 4,175
Net loss	(25,297)	$ (13,845)	(60,117)	$ (22,858)
Accounting Standards Update 2014-09 | Balances Without Adoption of ASU 2014-09
Statement of operations:
Revenue from services	15,838		68,473
Cost of services	16,825		61,290
Income taxes	1,399		97
Net loss	(25,237)		(60,133)
Accounting Standards Update 2014-09 | Impact of Adoption of ASU 2014-09
Statement of operations:
Revenue from services	(835)		536
Cost of services	(740)		510
Income taxes	(35)		10
Net loss	$ (60)		$ 16