STOCKHOLDERS' EQUITY (Schedule of Stock Option Activity) (Details) - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Number of Shares
Outstanding, beginning balance (in shares)	7,078,932
Granted (in shares)	685,850
Exercised (in shares)	(737,986)
Canceled (in shares)	(109,361)
Outstanding, ending balance (in shares)	6,917,435	7,078,932
Options vested and exercisable (in shares)	5,543,179
Weighted-Average Exercise Price
Outstanding, beginning balance (in USD per share)	$ 22.70
Granted (in USD per share)	43.52
Exercised (in USD per share)	19.91
Canceled (in USD per share)	48.85
Outstanding, ending balance (in USD per share)	24.65	$ 22.70
Options vested and exercisable (in USD per share)	$ 21.71
Weighted- Average Remaining Contractual Term
Outstanding, Weighted-Average Remaining Contractual Term (in years)	5 years 4 months 17 days	5 years 6 months 21 days
Options vested and exercisable, Weighted-Average Remaining Contractual Term (in years)	4 years 7 months 6 days
Aggregate Intrinsic Value
Outstanding, Aggregate Intrinsic Value	$ 174,842	$ 145,613
Options vested and exercisable, Aggregate Intrinsic Value	$ 157,306