NET INCOME PER SHARE (Schedule of Basic and Diluted Net Income Per Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017		Sep. 30, 2018	Sep. 30, 2017
Earnings Per Share Reconciliation [Line Items]
Net income	$ 14,986	$ 8,030	[1]	$ 23,404	$ 11,874	[1],[2]
Basic net income per share:
Weighted-average common shares outstanding (in shares)	84,008	82,259	[1]	83,865	81,041	[1]
Basic net income per share attributable to common stockholders	$ 0.18	$ 0.10	[1]	$ 0.28	$ 0.15	[1]
Diluted net income per share
Weighted-average common shares outstanding (in shares)	84,008	82,259	[1]	83,865	81,041	[1]
Number of shares used in diluted calculation (in shares)	88,724	87,433	[1]	89,271	86,097	[1]
Diluted net income per share attributable to common stockholders (in USD per share)	$ 0.17	$ 0.09	[1]	$ 0.26	$ 0.14	[1]
Stock options
Diluted net income per share
Incremental common shares (in shares)	3,011	3,253		3,096	3,179
Restricted stock units
Diluted net income per share
Incremental common shares (in shares)	1,656	1,921		2,240	1,877
Employee stock purchase program
Diluted net income per share
Incremental common shares (in shares)	49	0		70	0

[1] As of January 1, 2018, the Company adopted ASC 606 using the full retrospective method. Accordingly, the Company has recast certain amounts in the prior periods presented. See Note 1 below for additional discussion.

[2] As of January 1, 2018, the Company adopted ASC 606 using the full retrospective method. Accordingly, the Company has recast certain amounts in the prior period presented. Also as of January 1, 2018, the Company adopted Accounting Standards Update No. 2016-18, "Statement of Cash Flows (Subtopic 230): Restricted Cash," and recast the prior period presented. See Note 1 below for additional discussion.