EQUITY STRUCTURE AND ACCOUNTS - Schedule of Treasury Stock Repurchase Activity (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Oct. 30, 2014
Shares Repurchase Program [Roll Forward]
Repurchases paid	$ (2,588,000)	$ (4,652,000)	$ (994,000)
2014 Share Repurchase Authorization Program | Class A common stock
Shares Repurchase Program [Roll Forward]
Authorizations remaining at beginning of the year	44,353,000	49,006,000	$ 50,000,000
Additional authorizations	$ 0	$ 0		$ 50,000,000
Repurchases paid (in shares)	189,897	424,317	84,203
Repurchases paid	$ (2,584,000)	$ (4,653,000)	$ (994,000)
Repurchases unsettled	0	0	0
Authorizations remaining at the end of the year	$ 41,769,000	$ 44,353,000	$ 49,006,000