NET INCOME (LOSS) PER SHARE - Schedule of Earnings (Loss) Per Share and Dilutive Shares Information (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Basic net income (loss) per share
Net (loss) income	$ (13,605)	$ (14,301)	$ (21,048)	$ 33,824	$ (27,906)	$ 12,776
Denominator (in shares)	64,480		63,719		64,405	63,611
Basic net (loss) income per share (in dollars per share)	$ (0.21)		$ (0.33)		$ (0.43)	$ 0.20
Add effect of diluted securities:
Stock options and equivalents and convertible debt (in shares)	0		0		0	496
Denominator for diluted net income (loss) per share (in shares)	64,480		63,719		64,405	64,107
Diluted net (loss) income per share (in dollars per share)	$ (0.21)		$ (0.33)		$ (0.43)	$ 0.20
Potentially dilutive common shares:
Total potentially dilutive common shares (in shares)					24,499	21,833
Convertible debt
Potentially dilutive common shares:
Total potentially dilutive common shares (in shares)					17,931	17,931
Stock options and equivalents
Potentially dilutive common shares:
Total potentially dilutive common shares (in shares)					6,568	3,902