EQUITY STRUCTURE AND ACCOUNTS - Additional Information (Details)	6 Months Ended
	Jun. 30, 2019 USD ($) Vote Class_of_Stock $ / shares shares	Jun. 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 | $	$ 41,100,000
Percentage of aggregate common stock outstanding under Repurchase Program	2.30%
Closing price (in dollars per share) | $ / shares	$ 16.61
Series REIT LP Units
Class of Stock [Line Items]
Exchange of noncontrolling interest for common stock, units exchanged (in shares)	1,139,411	4,349,832
Series TRS LP Units
Class of Stock [Line Items]
Exchange of noncontrolling interest for common stock, units exchanged (in shares)	1,139,411	4,349,832
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)	1,139,411
Exchange of noncontrolling interest for common stock (in shares)		4,349,832
Class A Common Stock | 2014 Share Repurchase Authorization Program
Class of Stock [Line Items]
Additional authorizations | $	$ 0	$ 0			$ 50,000,000.0
Purchase of treasury stock (in shares)	40,065	40,065
Remaining amount available for repurchase | $	$ 41,132,000	$ 41,769,000	$ 41,769,000	$ 41,769,000
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)	(1,139,411)
Exchange of noncontrolling interest for common stock (in shares)		(4,349,832)