STOCKHOLDERS' EQUITY (Schedule of Stock Option Activity) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Number of Shares
Outstanding, beginning balance (in shares)	7,078,932
Granted (in shares)	671,250
Exercised (in shares)	(313,437)
Canceled (in shares)	(44,397)
Outstanding, ending balance (in shares)	7,392,348	7,078,932
Options vested and exercisable (in shares)	5,642,395
Weighted- Average Exercise Price
Outstanding, beginning balance (in USD per share)	$ 22.70
Granted (in USD per share)	43.58
Exercised (in USD per share)	18.13
Canceled (in USD per share)	49.20
Outstanding, ending balance (in USD per share)	24.63	$ 22.70
Options vested and exercisable (in USD per share)	$ 20.94
Weighted- Average Remaining Contractual Term
Outstanding, Weighted-Average Remaining Contractual Term (in years)	5 years 9 months 22 days	5 years 6 months 22 days
Options vested and exercisable, Weighted-Average Remaining Contractual Term (in years)	4 years 10 months 2 days
Aggregate Intrinsic Value
Outstanding, Aggregate Intrinsic Value	$ 136,698	$ 145,613
Options vested and exercisable, Aggregate Intrinsic Value	$ 125,460