SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Equipment, Deferred Tax Asset, Revenue and Expense Recognition, Equity-Based Compensation and Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Deferred Tax Asset and Amount Due Pursuant to Tax Receivable Agreement
Percentage of tax benefits payable to partners under tax receivable agreement	85.00%
Remaining percentage of cash savings realized by the Company (as a percent)	15.00%
Revenue and Expense Recognition
Reimbursable expenses billed to clients	$ 3,251	$ 2,873
Equity-based Compensation
Minimum age of retiring employees required so that certain qualifying awards granted during employment will not be forfeited	54 years
Consecutive years of service of retiring employees required so that certain qualifying awards granted during employment will not be forfeited	8 years
Income Taxes
Unrecognized tax benefits	$ 0	0
Unrecognized tax benefits, interest and penalties	$ 0	$ 0
Office equipment and furniture and fixtures | Minimum
Equipment and leasehold improvements
Useful lives	3 years
Office equipment and furniture and fixtures | Maximum
Equipment and leasehold improvements
Useful lives	7 years