COST OF REVENUE (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cost of Revenue [Abstract]
Compensation and benefits	$ 264,796	$ 261,839	$ 255,889
Outside fees and services	302,156	248,278	243,325
Reimbursable expenses	52,011	107,344	137,634
Technology and telecommunications	44,295	43,177	48,834
Depreciation and amortization	26,787	26,689	21,498
Total	$ 690,045	$ 687,327	$ 707,180