EQUITY STRUCTURE AND ACCOUNTS - Schedule of Treasury Stock Repurchase Activity (Details) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2016	Dec. 31, 2015	Oct. 30, 2014	Feb. 10, 2014
Class of Stock [Line Items]
Share price (in dollars per share)				$ 17.00
Shares Repurchase Program [Roll Forward]
Repurchases paid	$ (4,652,000)	$ (994,000)
2014 Share Repurchase Authorization Program
Class of Stock [Line Items]
Percentage of aggregate common stock outstanding under Repurchase Program	5.10%
2014 Share Repurchase Authorization Program | Class A common stock
Class of Stock [Line Items]
Authorized amount of stock repurchase	$ 0		$ 50,000,000
Treasury stock acquired, average cost (in dollars per share)	$ 10.96
Share price (in dollars per share)	$ 13.24
Shares Repurchase Program [Roll Forward]
Authorizations remaining as of December 31, 2015	$ 49,006,000
Additional authorizations	$ 0		$ 50,000,000
Repurchases paid (in shares)	424,317
Repurchases paid	$ (4,653,000)
Repurchases unsettled	0
Authorizations remaining as of September 30, 2016	$ 44,353,000	$ 49,006,000