EQUITY STRUCTURE AND ACCOUNTS - Additional Information (Details)															3 Months Ended								12 Months Ended
	Nov. 07, 2017 $ / shares	Sep. 01, 2017 $ / shares	Jun. 01, 2017 $ / shares	Mar. 01, 2017 $ / shares	Jan. 24, 2017 USD ($) shares	Dec. 02, 2016 $ / shares	Sep. 01, 2016 $ / shares	Jun. 01, 2016 $ / shares	Apr. 01, 2016 $ / shares	Dec. 01, 2015 $ / shares	Sep. 01, 2015 $ / shares	Jun. 08, 2015 $ / shares	Mar. 12, 2015 $ / shares	Jan. 01, 2015 USD ($) $ / shares	Dec. 31, 2017 USD ($) $ / shares	Sep. 30, 2017 $ / shares	Jun. 30, 2017 $ / shares	Mar. 31, 2017 $ / shares	Dec. 31, 2016 USD ($) $ / shares	Sep. 30, 2016 $ / shares	Jun. 30, 2016 $ / shares	Mar. 31, 2016 $ / shares	Dec. 31, 2017 USD ($) Vote Class_of_Stock $ / shares shares	Dec. 31, 2016 USD ($) $ / shares shares	Dec. 31, 2015 USD ($) $ / shares shares	Dec. 31, 2014 USD ($)	Oct. 30, 2014 USD ($)
Class of Stock [Line Items]
Number of classes of common stock | Class_of_Stock																							2
Purchase of treasury stock																							$ 2,588,000	$ 4,652,000	$ 994,000
Earnings and Profits (E&P) distribution requirement														$ 48,300,000
Earnings and Profits (E&P) distribution requirement (in dollars per share) | $ / shares														$ 0.90
Dividends paid																							$ 105,921,000	$ 74,393,000	$ 57,390,000
Dividends per share of common stock (in dollars per share) | $ / shares															$ 0.315	$ 0.3	$ 0.3	$ 0.3	$ 0.46	$ 0.275	$ 0.275	$ 0.275
2014 Share Repurchase Authorization Program
Class of Stock [Line Items]
Percentage of aggregate common stock outstanding under Repurchase Program															3.50%								3.50%
Share price (in dollars per share) | $ / shares															$ 13.63								$ 13.63
Series REIT LP Units
Class of Stock [Line Items]
Exchange of noncontrolling interest for common stock, units exchanged (in shares) | shares																							20,767,407	10,521,149	3,586,546
Series TRS LP Units
Class of Stock [Line Items]
Exchange of noncontrolling interest for common stock, units exchanged (in shares) | shares																							20,767,407	10,521,149	3,586,546
Class A common stock
Class of Stock [Line Items]
Number of votes per share | Vote																							1
Exchange of noncontrolling interest for common stock (in shares) | shares																							20,767,407	10,521,149	3,586,546
Dividends paid					$ 20,800,000
Dividends, share-based compensation stock value					$ 700,000
Common stock issued as dividends (in shares) | shares					815,819
Common stock equivalent dividends paid					$ 11,500,000
Dividends per share of common stock (in dollars per share) | $ / shares	$ 0.315	$ 0.3	$ 0.3	$ 0.3		$ 0.46	$ 0.275	$ 0.275	$ 0.275	$ 1.45	$ 0.275	$ 0.25	$ 0.25										$ 1.215	$ 1.285	$ 2.225
Common stock, dividends, weighted average price per share | $ / shares																			$ 14.06
Class A common stock | 2014 Share Repurchase Authorization Program
Class of Stock [Line Items]
Authorized amount of stock repurchase															$ 0				$ 0				$ 0	$ 0			$ 50,000,000
Purchase of treasury stock (in shares) | shares																							189,897	424,317	84,203
Treasury stock acquired, average cost (in dollars per share) | $ / shares																							$ 13.61	$ 10.96	$ 11.81
Purchase of treasury stock																							$ 2,584,000	$ 4,653,000	$ 994,000
Remaining amount available for repurchase															$ 41,769,000				$ 44,353,000				$ 41,769,000	$ 44,353,000	$ 49,006,000	$ 50,000,000
Class B common stock
Class of Stock [Line Items]
Number of votes per share | Vote																							1
Exchange of noncontrolling interest for common stock (in shares) | shares																							(20,767,407)	(10,521,149)	(3,586,546)
Common stock issued as dividends (in shares) | shares					432,314
Series REIT LP Units
Class of Stock [Line Items]
Common stock issued as dividends (in shares) | shares					1,248,133