STOCKHOLDERS EQUITY (Details) $ / shares in Units, $ in Thousands		1 Months Ended			4 Months Ended	9 Months Ended	12 Months Ended
	Jan. 11, 2017 shares	Jan. 31, 2017 $ / shares shares	Nov. 30, 2014 $ / shares shares	Apr. 30, 2014 shares	Apr. 21, 2014 shares	Dec. 31, 2014 shares	Dec. 31, 2016 USD ($) shares	Dec. 31, 2015 USD ($) shares	Dec. 13, 2016 $ / shares
Stockholders Equity
Treasury stock shares acquired (in shares)							124,268	263,622
Treasury stock shares acquired | $							$ 3,314	$ 7,616
Special dividend declared (in dollars per share) | $ / shares									$ 1.25
Group LP
Stockholders Equity
Number of units held by noncontrolling interest holders								33,803,921
Group LP
Stockholders Equity
Number of units held by noncontrolling interest holders							33,698,300
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	7,699,851
Shares issued (in shares)						7,483,442
Common Stock issued in connection with settlement of appreciation rights issued in prior years (in shares)				88,802
Issuance of Class A common stock and acquisition of Class A partnership units in connection with follow-on offering (in shares)						4,511,058
Common stock, shares issued							20,948,998	20,536,740
Common stock, shares outstanding			19,770,893				20,561,108	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
Shares issued (in shares)				7,475,000
Class A common stock | Follow-on Offering
Stockholders Equity
Shares issued (in shares)	5,750,000		4,509,400
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 follow-on offering (in shares)			4,511,058
Class A common stock | Group LP
Stockholders Equity
Common stock, shares outstanding							20,561,108
Class B common stock
Stockholders Equity
Shares issued (in shares)				36,158,698	36,158,698
Issuance of Class A common stock and acquisition of Class A partnership units in connection with follow-on offering (in shares)						(4,507,453)
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 | Follow-on Offering
Stockholders Equity
Issuance of Class A common stock and acquisition of Class A partnership units in connection with follow-on offering (in shares)			4,507,453
Shares converted			2,998,322
Shares issued upon conversion			1,658
Conversion ratio			0.00055
Number of shares repurchased and retired		5,356,876	1,509,131
Price per share of stock which was repurchased and retired | $ / shares		$ 101	$ 28