EQUITY STRUCTURE AND ACCOUNTS - Additional Information (Details)									3 Months Ended			9 Months Ended		12 Months Ended
	Sep. 01, 2017 $ / shares	Jun. 01, 2017 $ / shares	Mar. 01, 2017 $ / shares	Jan. 24, 2017 USD ($) shares	Sep. 01, 2016 $ / shares	Jun. 01, 2016 $ / shares	Mar. 01, 2016 $ / shares	Jan. 01, 2015 USD ($) $ / shares	Sep. 30, 2017 USD ($) $ / shares	Dec. 31, 2016 USD ($) $ / shares	Sep. 30, 2016 USD ($) $ / shares	Sep. 30, 2017 USD ($) Vote Class_of_Stock $ / shares shares	Sep. 30, 2016 USD ($) $ / shares shares	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Oct. 30, 2014 USD ($)
Class of Stock [Line Items]
Number of classes of common stock | Class_of_Stock												2
Purchase of treasury stock														$ 4,652,000
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												$ 76,757,000		74,393,000
2014 Share Repurchase Authorization Program
Class of Stock [Line Items]
Percentage of aggregate common stock outstanding under Repurchase Program									3.70%			3.70%
Share price (in dollars per share) | $ / shares									$ 13.78			$ 13.78
Series REIT LP Units
Class of Stock [Line Items]
Exchange of noncontrolling interest for common stock (in shares) | shares												(13,737,365)
Series TRS LP Units
Class of Stock [Line Items]
Exchange of noncontrolling interest for common stock (in shares) | shares												(13,737,365)
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												13,737,365
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	$ 0.300	$ 0.300	$ 0.300		$ 0.275	$ 0.275	$ 0.275		$ 0.300	$ 0.46	$ 0.275	$ 0.900	$ 0.825
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			$ 50,000,000.0
Purchase of treasury stock (in shares) | shares												0	424,317
Treasury stock acquired, average cost (in dollars per share) | $ / shares													$ 10.96
Purchase of treasury stock												$ 0	$ 4,653,000
Remaining amount available for repurchase									$ 44,353,000	$ 44,353,000	$ 44,353,000	$ 44,353,000	$ 44,353,000	$ 44,353,000	$ 49,006,000
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												(13,737,365)
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