INCOME TAXES - Unrecognized Tax Benefit Activity (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance at the beginning of the period	$ 4,739	$ 3,257	$ 7,138
Additions related to prior year tax positions	2,019	420	1,458
Additions related to current year tax positions	610	2,053	472
Reductions related to settlements with taxing authorities	(131)	0	(1,517)
Reductions related to expiration of the applicable statute of limitations	0	(991)	(4,294)
Balance at the end of the period	$ 7,237	$ 4,739	$ 3,257