EQUITY STRUCTURE AND ACCOUNTS - Additional Information (Details) $ / shares in Units, $ in Thousands	9 Months Ended
	Sep. 30, 2019 USD ($) Vote Class_of_Stock $ / shares shares	Sep. 30, 2018 USD ($) shares	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Oct. 30, 2014 USD ($)
Class of Stock [Line Items]
Number of classes of common stock | Class_of_Stock	2
2014 Share Repurchase Authorization Program
Class of Stock [Line Items]
Remaining amount available for repurchase | $	$ 41,100
Percentage of aggregate common stock outstanding under Repurchase Program	2.20%
Closing price (in dollars per share) | $ / shares	$ 17.27
Series REIT LP Units
Class of Stock [Line Items]
Exchange of noncontrolling interest for common stock, units exchanged (in shares)	1,140,000	4,549,832
Series TRS LP Units
Class of Stock [Line Items]
Exchange of noncontrolling interest for common stock, units exchanged (in shares)	1,140,000	4,549,832
Class A Common Stock
Class of Stock [Line Items]
Number of votes per share | Vote	1
Exchange of noncontrolling interest for common stock, units exchanged (in shares)	1,140,000
Exchange of noncontrolling interest for common stock (in shares)		4,549,832
Class A Common Stock | 2014 Share Repurchase Authorization Program
Class of Stock [Line Items]
Additional authorizations | $		$ 0			$ 50,000
Purchase of treasury stock (in shares)	40,065	0
Remaining amount available for repurchase | $	$ 41,132	$ 41,769	$ 41,769	$ 41,769
Class B Common Stock
Class of Stock [Line Items]
Number of votes per share | Vote	1
Exchange of noncontrolling interest for common stock, units exchanged (in shares)	(1,140,000)
Exchange of noncontrolling interest for common stock (in shares)		(4,549,832)