REVENUE RECOGNITION - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2018	Jun. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Revenue from Contract with Customer [Abstract]
Deferred revenue			$ 70,400	$ 64,100
Deferred revenue recognized during period	$ 36,500	$ 58,000
Deferred revenue	66,666	66,666			$ 62,371
Noncurrent deferred revenue	700	700
Amortization expense recognized related to contract cost assets	13,200	36,900
Current contract assets	37,300	37,300
Noncurrent contract assets	$ 4,600	$ 4,600