STOCKHOLDERS EQUITY (Details) $ in Thousands	1 Months Ended		9 Months Ended
	Nov. 30, 2014 USD ($) shares	Apr. 30, 2014 shares	Sep. 30, 2016 USD ($) shares	Sep. 30, 2015 USD ($) shares	Dec. 31, 2015 shares
Stockholders Equity
Treasury stock shares acquired (in shares)			98,126	242,619
Treasury stock shares acquired | $			$ 2,621	$ 7,006
Group LP
Stockholders Equity
Number of units held by noncontrolling interest holders			33,698,300		33,803,921
Noncontrolling interests (as a percent)			62.00%		63.00%
Class A common stock
Stockholders Equity
Aggregate stock issuance (in shares)		15,263,653
Reorganization of equity structure (in shares)		7,699,851
Common Stock issued in connection with settlement of appreciation rights issued in prior years (in shares)		88,802
Common stock, shares issued			20,894,035		20,536,740
Common stock, shares outstanding			20,532,287		20,273,118
Number of shares of common stock to be issued upon exchange of a partnership unit		1	1
Class A common stock | IPO
Stockholders Equity
Common Stock issued (in shares)		7,475,000
Class A common stock | Secondary Offering
Stockholders Equity
Issuance of new and sale of existing common stock (in shares)	6,325,000
Issuance of Class A common stock and acquisition of Class A partnership units in connection with secondary offering (in shares)	4,511,058
Class A common stock | Group LP
Stockholders Equity
Common stock, shares outstanding			20,532,287
Class B common stock
Stockholders Equity
Common Stock issued (in shares)		36,158,698
Common stock, shares issued			31,138,193		31,229,236
Common stock, shares outstanding			31,138,193		31,229,236
Ratio of subscription price to the initial public offering price of shares of common stock		0.00055
Dividends payable ratio to outstanding shares of publicly traded common stock		0.00055
Class B common stock | Secondary Offering
Stockholders Equity
Shares converted	2,998,322
Shares issued upon conversion	1,658
Conversion ratio	0.00055
Number of shares repurchased and retired	1,509,131
Value of stock repurchased and retired | $	$ 28
Class B common stock | Maximum
Stockholders Equity
Aggregate number of shares of Class B common stock that may be converted into Class A common stock		20,000