EARNINGS PER SHARE - Net Income and Weighted Average Shares Outstanding (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Weighted average shares outstanding:
Basic (in shares)									81,902,524	61,998,089	51,702,188
Diluted (in shares)									109,704,880	107,638,788	51,870,808
Class A common stock
Earnings Per Share
Basic Net income (loss) available for Class A common shareholders	$ 36,106	$ 23,587	$ 22,113	$ 13,470	$ 41,856	$ 27,608	$ 2,802	$ (5,539)	$ 95,276	$ 66,727	$ 73,821
Diluted Net income (loss) available for Class A common shareholders									$ 124,046	$ 114,156	$ 73,821
Weighted average shares outstanding:
Basic (in shares)									81,902,524	61,998,089	51,702,188
Diluted (in shares)									109,704,880	107,638,788	51,870,808