STOCKHOLDERS EQUITY (Details) $ in Thousands			1 Months Ended		9 Months Ended
	Jul. 28, 2017 USD ($) shares	Jan. 11, 2017 USD ($) shares	Nov. 30, 2014 USD ($) shares	Apr. 30, 2014 shares	Sep. 30, 2017 USD ($) shares	Sep. 30, 2016 USD ($) shares	Dec. 31, 2016 shares
Stockholders Equity
Treasury stock shares acquired (in shares)					264,710	98,126
Treasury stock shares acquired | $					$ 9,832	$ 2,621
Group LP
Stockholders Equity
Number of units held by noncontrolling interest holders					22,605,843		33,698,300
Noncontrolling interests (as a percent)					40.00%		62.00%
Class A common stock
Stockholders Equity
Aggregate stock issuance (in shares)				15,263,653
Common stock, shares issued					33,899,875		20,948,998
Common stock, shares outstanding					33,247,275		20,561,108
Number of shares of common stock to be issued upon exchange of a partnership unit				1	1
Class A common stock | Follow-on Offering
Stockholders Equity
Issuance of new and sale of existing common stock (in shares)	6,000,000	5,750,000	6,325,000
Issuance of Class A common stock and acquisition of Class A partnership units in connection with follow-on offering (in shares)	5,680,903	5,356,876	4,511,058
Class A common stock | Group LP
Stockholders Equity
Common stock, shares outstanding					33,247,275		20,561,108
Class B common stock
Stockholders Equity
Shares issued (in shares)				36,158,698
Common stock, shares issued					20,045,736		31,138,193
Common stock, shares outstanding					20,045,736		31,138,193
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
Shares converted			2,998,322
Shares issued upon conversion			1,658
Conversion ratio			0.00055
Number of shares repurchased and retired	5,680,903	5,356,876	1,509,131
Value of stock repurchased and retired | $	$ 128	$ 101	$ 28