NET INCOME (LOSS) PER SHARE - Basic and Diluted EPS (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Numerator:
Income (loss) from continuing operations, basic									$ 59,536	$ (18,760)	$ (73,530)
Loss from discontinued operations, basic									0	0	(94,934)
Net income (loss), attributable to common stockholders, basic	$ 25,883	$ 15,033	$ 14,597	$ 4,435	$ 4,301	$ (4,584)	$ (7,810)	$ (10,667)	59,536	(18,760)	(168,464)
Add: Interest expense on 2023 Notes									5,790	0	0
Net income (loss) attributable to common stockholders, diluted									$ 65,326	$ (18,760)	$ (168,464)
Denominator:
Weighted-average shares used to compute basic net income (loss) per share									110,280	115,372	112,059
Dilutive effect of 2023 Notes									12,541	0	0
Dilutive effect of options and awards granted under equity incentive plan and employee stock purchase plan									412	0	0
Weighted-average shares used to compute diluted net income (loss) per share									123,233	115,372	112,059
Net income (loss) per share
Basic (in dollars per share)									$ 0.54	$ (0.16)	$ (1.50)
Diluted (in dollars per share)									$ 0.53	$ (0.16)	$ (1.50)