NET INCOME (LOSS) PER SHARE (Schedule of Basic and Diluted Net Loss Per Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Numerator:
Net income (loss)		$ 152,858	$ (4,670)	$ (32,900)
Allocation of undistributed earnings for basic calculations		$ 152,858
Denominator:
Number of shares used in basic calculation (in shares)	[1]	81,602	77,186	74,683
Basic net income (loss) per share attributable to common stockholders (in dollars per share)		$ 1.87	$ (0.06)	$ (0.44)
Numerator:
Allocation of undistributed earnings for basic calculations		$ 152,858
Reallocation of undistributed earnings as a result of conversion from Class B to Class A shares		0
Allocation of undistributed earnings		$ 152,858
Denominator:
Number of shares used in basic calculation (in shares)	[1]	81,602	77,186	74,683
Weighted-average effect of dilutive securities
Conversion of Class B to Class A common shares outstanding (in shares)		0
Number of shares used in diluted calculation (in shares)	[1]	87,170	77,186	74,683
Diluted net income (loss) per share attributable to common stockholders (in dollars per share)		$ 1.75	$ (0.06)	$ (0.44)
Common Class A
Numerator:
Net income (loss)			$ (4,296)	$ (28,694)
Allocation of undistributed earnings for basic calculations			$ (4,296)	$ (28,694)
Denominator:
Number of shares used in basic calculation (in shares)			70,997	65,135
Basic net income (loss) per share attributable to common stockholders (in dollars per share)			$ (0.06)	$ (0.44)
Numerator:
Allocation of undistributed earnings for basic calculations			$ (4,296)	$ (28,694)
Reallocation of undistributed earnings as a result of conversion from Class B to Class A shares			(374)	(4,206)
Allocation of undistributed earnings			$ (4,670)	$ (32,900)
Denominator:
Number of shares used in basic calculation (in shares)			70,997	65,135
Weighted-average effect of dilutive securities
Conversion of Class B to Class A common shares outstanding (in shares)			6,189	9,548
Number of shares used in diluted calculation (in shares)			77,186	74,683
Diluted net income (loss) per share attributable to common stockholders (in dollars per share)			$ (0.06)	$ (0.44)
Common Class B
Numerator:
Net income (loss)			$ (374)	$ (4,206)
Allocation of undistributed earnings for basic calculations			$ (374)	$ (4,206)
Denominator:
Number of shares used in basic calculation (in shares)			6,189	9,548
Basic net income (loss) per share attributable to common stockholders (in dollars per share)			$ (0.06)	$ (0.44)
Numerator:
Allocation of undistributed earnings for basic calculations			$ (374)	$ (4,206)
Reallocation of undistributed earnings as a result of conversion from Class B to Class A shares			0	0
Allocation of undistributed earnings			$ (374)	$ (4,206)
Denominator:
Number of shares used in basic calculation (in shares)			6,189	9,548
Weighted-average effect of dilutive securities
Conversion of Class B to Class A common shares outstanding (in shares)			0	0
Number of shares used in diluted calculation (in shares)			6,189	9,548
Diluted net income (loss) per share attributable to common stockholders (in dollars per share)			$ (0.06)	$ (0.44)
Stock options
Weighted-average effect of dilutive securities
Incremental common shares (in shares)		3,279
Stock options | Common Class A
Weighted-average effect of dilutive securities
Incremental common shares (in shares)			0	0
Stock options | Common Class B
Weighted-average effect of dilutive securities
Incremental common shares (in shares)			0	0
Restricted stock units
Weighted-average effect of dilutive securities
Incremental common shares (in shares)		2,289
Restricted stock units | Common Class A
Weighted-average effect of dilutive securities
Incremental common shares (in shares)			0	0
Restricted stock units | Common Class B
Weighted-average effect of dilutive securities
Incremental common shares (in shares)			0	0

[1] The structure of the Company’s common stock changed in the year ended December 31, 2016. Refer to Note 13 for details.