INCOME TAXES - Components of Income Before Income Taxes (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
Components of income before income taxes
Domestic									$ 25,232	$ 28,047	$ 50,563
Foreign									22,321	17,327	5,638
INCOME BEFORE INCOME TAXES	$ 41,196	$ (21,860)	$ 13,505	$ 14,712	$ 7,590	$ 21,296	$ 1,059	$ 15,429	$ 47,553	$ 45,374	$ 56,201